Talk:Gliese 581c/Archive 1

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References

I have found a grand total of one reference to the date of discovery for this planet. That is April 4th, 2007, cited on a Princeton website[1]. I changed the date in the article to correspond with that, but somebody has changed it back to April 23rd, seemingly without any reference. I have e-mailed the owner of the Princeton page asking for a primary source, but does anybody here actually have a citation for the date of discovery (of the planet, not of it's possibility of supporting life) being something else? —The preceding

Update: I now have primary documentation[2] for the date of discovery being April 4th, and I have so changed the information on the page.

I changed it to April 23rd because it is the original date of discovery in the article planet box since it was created, and lot more seemingly discovered on this date than on April 4. The The Extrasolar Planet Encyclopedia wasn't have this planet in the list till April 25th. I don't think that was that long ago; it wasn't this planet in any extrasolar planet websites till April 23rd the earliest. This planet was added to

BlueEarth

19:16, 26 April 2007 (UTC)

The discrepancy is easily explained by the news embargo which expired April 25, I believe. At least three Asian newspapers breached the embargo by several hours. The Extrasolar Planets Encyclopedia breached the embargo, also, if my understanding of the sequence of events is correct, but only by a little. Vegasprof 11:45, 27 April 2007 (UTC)

An online effort has been hinting at the existence of that planet before

[3] "In 2005, the Geneva team announced the detection of a Neptune-mass planet in a 5.366-day orbit around the star, and they published 20 high-precision radial velocities in support of their detection. These radial velocities have been in the systemic backend database since last summer, and so naturally, when today’s detection was announced, I was eager to see the models that our users have submitted for the Gl 581 planetary system. The six submitted fits with the lowest chi-square for the system — by flanker (fits 1,2), EricFDiaz (fits 3,5), eugenio (fit 4), and bruce01 (fit 6) — all contain both the known 5.366 day planet as well as a planet with properties (Msin(i)~5 Mearth, P~12.2 days) that are a near-match to the newly announced planet. In the following screenshot, I’ve highlighted Gl 581 b in blue and the newly confirmed Gl 581 c in light orange."

And so on. While the author doesn't want to - and especially mentions he doesn't want to - take away any pride for the discovery, because the team has met serious scientific requirements, unlike the online effort-I think it's notable enough to deserve a mention in the article. What do you think ?

That is quite notable, in my opinion, provided it is well-documented. (I haven't looked at the pictures yet.) Others may disagree. Vegasprof 02:17, 25 April 2007 (UTC)

Once again I agree with the Vegasprof. The work done by the enthusiasts (some of whom are professionals) at oklo.org is very exciting. It is a shame that their 'prediction' is not getting more attention, because I think this was part of the point of oklo.org. Unexpect 02:15, 7 May 2007 (UTC)

The Neptune class planet is another planet in the same solar system, not this one.~

What's the "c"?

What does the "581 c" on the end of its name mean? --Candy-Panda 10:43, 26 April 2007 (UTC)

The star is Gliese 581. All its planets are designated by letters following the star's designation omitting "a". In our case we have 3 detected planets, Gliese 581 b, Gliese 581 c and Gliese 581 d.Themanwithoutapast 11:49, 26 April 2007 (UTC)

Okay. So why not use "a" for the innermost planet? That is, if alien astronomers were observing our solar system, why would Mercury be "Xyrtsolm 398 b", Venus be "Xyrtsolm 398 c", Earth be "Xyrtsolm 398 d", etc.? Are they expecting the possibility of finding a planet even closer than Gliese 581 b? And if so, what happens if two planets are found closer than Gliese 581 b? GBC 15:40, 26 April 2007 (UTC)

I believe that the lettering suffix is not dependant on the actual position of the planet. Instead, it is dependant on the time it was discovered first. So, if an alien (using our naming methods) discovered Jupiter, they would append the suffix "b" to it. If they then discovered Neptune, it would be "c", and if they then discovered Earth, it would be "d". The reason that "a" is not used is because it may be confused with the star itself. So, for arguments sake, lets pretend that everysingle star already has the suffix of "a". It would make no sense to have two bodies with the same suffix. 80.189.214.73 16:16, 26 April 2007 (UTC)

Letters are given in the order of discovery, otherwise the system would become totally messed up as new planets are found. As an example, the planets in the 55 Cancri system are e, b, c, d the innermost super-Earth being the newest-found (more accurately, in the order of confirmation: existence of the planet d in that system was known earlier than planet c). Uppercase letters refer to stellar components: "A" is the first star, "B" second etc. Stellar component naming is more complicated as stellar systems tend to be hierarchical (e.g. one of the components turns out to be a binary).— JyriL ^talk 17:10, 26 April 2007 (UTC)

name?

Because of its importance, will this planet receive a name (and how? when?) or will it forever be Gliese 581 c?--Sonjaaa 21:33, 25 April 2007 (UTC)

I will name it Magsa.

BlueEarth

21:56, 25 April 2007 (UTC)

Is its discoverer called Stephen or Stephane or Stéphane? I guess I'd call it Stephania. ;) --Sonjaaa 22:35, 25 April 2007 (UTC)

Per current

IAU policy, it will be named Gliese 581 c for the foreseeable future. Further speculation on naming is contraindicated by Wikipedia:No original research and Wikipedia:What Wikipedia is not. Michaelbusch

22:36, 25 April 2007 (UTC)

"contraindicated?" Excuse me? 134.50.14.31 14:11, 27 April 2007 (UTC)

Did somebody delete some comments and questions I added to the discussion?? Is that allowed?--Sonjaaa 16:36, 27 April 2007 (UTC)

Named after...

"Gliese 581 c and its star, Gliese 581, are named after the German astronomer Wilhelm Gliese."

Well, the star is named after Wilhelm Gliese, but the planet is named using what seems to be a conventional naming method. It is the second planet from its sun, Gliese 581, and is thus given the letter (c) to designate it's position.... I'm going to go ahead and change it now. If you do revert, please respond letting me know why.

The freddinator 01:48, 26 April 2007 (UTC)

Sorry but the convention is by order discovered not distance from star, see "55 Cancri" e,b,c,f,d - GabrielVelasquez (talk) 02:47, 23 December 2007 (UTC)

This piece of random trivia does not belong in the introduction. A much better place is to add Gliese Catalogue of Nearby Stars to the "See also" section. mdf 12:05, 26 April 2007 (UTC)

the star isn't "named after Gliese" in the same sense Halley is named after Halley. "Gliese" is for "Gliese Catalogue". I'm sure Gliese was an important man, but even so they wouldn't have named 3,800 stars after him. It's just a reference to the catalogue.

dab (𒁳)

14:40, 26 April 2007 (UTC)

"Ymir" now seems to be quite popular in use, even outside the Geochemical News page. Time to add it here, I think. Danjel 16:37, 9 October 2007 (UTC)

Mass

Smallest Extrasolar Planet Yet Discovered?

The unsigned comment above was mine, in reponse to Eloquence, the orignal claim in the article was not that this was the smallest possibly habitable planet yet found, the orignal claim stated this was the smallest planet *EVER* found. That claim was simply not true. Rberger909 15:46, 25 April 2007 (UTC)rberger909

Probably not. There is a larger than 50% probability that

Where do you get 50% from? Everything is estimates and errors, but (excluding the pulsar planets) this is likely the smallest exoplanet yet found. The error bars on the OGLE planet are quite large - the upper 3 sigma limit is 11 Earth masses, not 10 - whereas the value for Gl 581 c, although a minimum, is likely very close to the actual value. Spiral Wave 23:37, 26 April 2007 (UTC)

If the true mass of Gliese 851 c exceeds 5.5 Earth masses, the probability for OGLE-2005-BLG-390Lb being less massive is larger than 50%, because this is its median mass. Even if the mass of Gliese 851 c is exactly 5 Earth masses, the chances for it being less massive than OGLE-2005-BLG-390Lb are not far from 50:50. MD:astronomer 00:27, 28 April 2007 (UTC)

Ah, of course, thanks. Silly me. Nonetheless, a 50% (or thereabouts; and either way) probability shouldn't be neglected. Perhaps both this and the OGLE planet's articles should reflect that they're both contenders, but the absolute smallest is unknown? Spiral Wave 18:50, 29 April 2007 (UTC)

Corrrections to mass and eccentricity

The reference pre-print [4] indicates the mass is 5.03 earth masses and eccentricity is .28 +/- .06, so the figures cited in the article seem to be wrong. Is the embargo still in effect? I think [5] is the original source, so those figures have to be "correct" Rich.lewis 13:45, 25 April 2007 (UTC)

Is the article still embargoed? I'd like to correct the facutal errors. Looks like the incorrect data came from SIMBAD. I'm sure the pre-print is more correct 131.107.0.73 15:58, 25 April 2007 (UTC)

I found the parenthetical regarding 5.03 Earth masses to be confusing. The use of the pronoun "it" seems to be part of the problem. The sentence should be expanded to explain the circumstances in which 5.03 is the correct figure.Nissynis 17:08, 25 April 2007 (UTC)

Looks like this got resolved, all the facts are right now (thanks someone) Rich.lewis 16:33, 27 April 2007 (UTC)

Mass 4.83 M?

The table says 4.83M whereas the article (and relevant sources) says 5.03M. Where does this 4.83 come from?

I noticed this earlier, see my comment on mass and eccentricity errors above. The 4.83 figure is cited y the exoplanet encylcopedia, but I agree 5.03 seems to be the more current measurement. But both have support by some scientific reference, not sure which is correct. http://vo.obspm.fr/exoplanetes/encyclo/star.php?st=Gl+581 Rich.lewis 01:18, 27 April 2007 (UTC)

The discovery paper gives two different models for this system, a 2-planet model (in which the mass of planet "c" is 4.83 times that of the Earth), and a 3-planet model (in which the mass is 5.03 times the mass). Extrasolar Planets Encyclopaedia seems to have taken the parameters of the second planet from the 2-planet model, and the third planet from the 3-planet model (obviously, it isn't in the 2-planet model!). We probably shouldn't mix-and-match models like this, so I'd go for the higher estimate. Chaos syndrome 10:36, 27 April 2007 (UTC)

I removed the following from the end of the Mass section:

(The citation does not seem to address the stability, in fact)

because it belongs here rather than in the article itself. I don't have the expertise to address it, though -- anybody have thoughts? (The comment was regarding Udry et al. (2007).) -SD 75.7.38.24 01:53, 13 June 2007 (UTC)

Super Earth

Just to clarify. The term "Super-Earth" is not only used by the media. It has become the term used in scientific articles to describe planets with masses between about 3, 4 or 5 times Earth masses (below that they are called "Earth-sized") and Neptune class planets. Themanwithoutapast 20:52, 27 April 2007 (UTC)

Gas giants" are called "Terrestrial" so I have to disagree that "Super Earth" is the appropriate term. Just because this encyclopedia chooses to pander to the media at times doesn't make it correct or accurate. Articles or not, personal preference isn't science. What about "Super-Venus," "Super-Mars," "Super-Mercury," "Super-Pluto," "Super-Ganymede?" ...I hope that some sense occurs in the land of Wikipedia and the term "Super-Terrestrial" becomes the main title of the article now titled "Super-Earth." {Terrestrial_planet} - GabrielVelasquez (talk

) 19:56, 29 December 2007 (UTC)

I personally don't care which way it is. Terrestrial means "Earth-like". :p --Marhawkman (talk) 19:50, 30 December 2007 (UTC)

FALSE; it does not. Soil-Like, Dirt-Like, Rock-Like, terra-firma, Like our own planet Earth - These are all different, and you can only say you don't care if you don't care about the difference either. Unless you actually believe that "Earth-Like" is the perfect synonym of "Soil-Like," in which case I would tell you that if my gifts lay as a farmer/gardener not an astronomer/scientist, that is where I would be spending my time. When the use of a term starts to look deceptive to people who appreciate logic and cogent reasoning I'm compelled to draw the line. "Non-Gas-Giant-Like" is what we are talking about, and using the word Earth to describe that is a misnomer, a grave misnomer, and borderline deceptive. "Earth-like" is one step down on the scale from Twin-of-Earth; I hope you enjoy your stay at the beach on this so called "Earth-like" planet... (Oh please, allow me to pay for your swim-wear!). In case you missed it, 504.62% of the solar constant at periastron would kill you if the pressure didn't (Think of Venus' ninty-two atmospheres of pressure times 5.03 for gliese 581c's minimum mass, times 0.815 for Venus mass: roughly 377 atmospheres). What does that plain fact (on heat) mean to you? The heat is less disputable than the star actually still being there now (supernovae) after the light took 20.4 years to get here! Plain and simple, without (can you say the same) any personal bias or agenda it is catagorically most like Venus, and therefore SUPER-VENUS (not Super-Soil) is best, but no one else is using that term yet so Super-Terrestrial is next best. Please refrain from the bias of

Geocentricity. There is nothing that this planet has in common with Earth that it has relatively less in common with Jupiter. Jupiter and Earth are not the only planets in our solar system. Even if it is relatively close in mass, its still as foolish as refering to the Earth as Super-Moon (Super-Luna). GabrielVelasquez (talk

) 05:47, 5 January 2008 (UTC)

Wiktionary disagrees. "1: Of, relating to, or inhabiting the land of the Earth or its inhabitants 2: Of, relating to, or composed of land." Using definition 1 would give you approximately the same as "earth-like". You're really missing the point here. This isn't Star Trek. Terrestrial/Earth-like doesn't indicate that a planet is habitable. It indicates that it has a physical composition similar to that of Earth. Although we don't know this one's composition, considering it's size and location, that is most likely. Yes it is probably most like Venus. But Venus is classified as a terrestrial planet.--Marhawkman (talk) 08:13, 5 January 2008 (UTC)

Radius

When I first looked at the page, the radius was listed as “1.22474487139 R[E]”. This was then rounded to 1.225 by Stereo. However, 1.22474487139 is the sqare root of 1.50, suggesting someone made a rather dumb assumption based on “the new planet is about 50 percent bigger than Earth”. If someone has a cite with useful info backing up such an amazing coincidence, I’d like to see it. -Ahruman 21:55, 24 April 2007 (UTC)

I took out the radius value again, becuase another source speaks of a 50% greater diameter rather than a 50% greater profile area (which doesn’t make much sense anyway; also, a 1.2x radius with a 5x mass would mean a density greater than solid lead). I didn’t include the 1.5 radius value because said other source references a press release which is not online at this time, meaning the veracity of that value can’t be verified (although I’m inclined to believe it’s correct). -Ahruman 23:27, 24 April 2007 (UTC)

I made up the equation about how to calculate the planet's radius: (M_planet⁻³ × R_star⁻² ÷ a⁻⁴)⁻².

For Gliese 581 c: (5.03⁻³ × 0.465⁻² ÷ 0.073⁻⁴)⁻² ≈ (2.25)⁻² = 1.5 R_Earth

How do you get this equation?

I made this equation by figuring out how to set it up. There is an example above about trying to get the right answer of R_earth as it agree with reliable source using the variable R_star.

BlueEarth

17:59, 29 April 2007 (UTC)

This paper http://arxiv.org/abs/0704.3454v1 by Valencia and Sasselov has the following formula

R_planet/R_earth = (1+0.56k)(M_planet/M_earth)^{0.262(1-0.138k)},

where k is the percentage of water in the planet. Temur 02:45, 29 April 2007 (UTC)

I had long chat with the NASA ppl last night, ppl who discovered the planet were hard to get, and since some of NASA ppl were saying few thing about it. I called

The density given is 6.8x10⁵ kg/m³. That's six times denser than lead and three times denser than plutonium. Where did this "50% bigger" figure come from, and what is it actually supposed to mean? I don't believe it's either 50% bigger by volume or 50% bigger by radius. --Chronodm 05:21, 25 April 2007 (UTC)

About density, since ρ = m / V (Earth mass and volume), ρ' = 5M / ( 1.33 · π · (1.5r)^3 ) = ( 5 / 3.375 ) ρ = 1.49 ρ = 8,300 kg · m^-3 212.51.52.8 09:49, 25 April 2007 (UTC)

Ah, okay, so it's just the density figure that was badly wrong. And now that I've done the math again *after* the day's first cup of coffee, I'll believe 50% bigger by radius. --Chronodm 10:48, 25 April 2007 (UTC)

The paragraph about density and gravity is poorly written. It states:

Under the assumption that it is a rocky planet, rather than an icy planet, Gliese 581 c has a radius 50% larger than Earth... On the other hand, if it has approximately the same density as Earth, its radius would be 1.7 times bigger...

The "On the other hand" implies, first that Earth is not a rocky planet, and/or second, that Earth is less dense than a rocky planet. In fact, Earth is the densest major body in our solar system. Properly, "On the other hand" should be followed by the radius of Gliese 581 c should it be an icy planet. I have made a minimalist change to render this paragraph acceptable; I removed the "On the other hand". --24.137.81.76 01:34, 27 April 2007 (UTC)

Gravity

1.6g is not accurate. It's a simple calculus, since g = G M / r^2 (Earth mass and radius), new planet g' = G 5M / (1.5r)^2 = ( G M / r^2 ) · ( 5 / 1.5^2 ) = 2.2 g, meaning surface gravity would be a 120% of Earth's, and not a 60% (it means: 2.2g instead of 1.6g).212.51.52.7 09:43, 25 April 2007 (UTC)

The article that cites the 1.6g is contradictory in itself as well, as it states the following: The new planet is about five times heavier than Earth. Its discoverers aren't certain if it is rocky like Earth or if its a frozen ice ball with liquid water on the surface. If it is rocky like Earth, which is what the prevailing theory proposes, it has a diameter about 1 1/2 times bigger than our planet. If it is an iceball, as Mayor suggests, it would be even bigger. but than assumes certain specific values for its radius and mass to determine the 1.6g value. We should probably only say in the article that assuming the planet is rocky and not icy and therefore assuming a radius of 1.5 R(E) and a mass of 5 M(E) gravity at the surface would be 2.2g (which is rather high and may be problematic for any lifeforms). Themanwithoutapast 09:51, 25 April 2007 (UTC)

Well as the article states the mass as ~4.83 ME, we should use ( 4.83 / 1.5^2 ) = 2.1466.. = ~2.1 —The preceding

unsigned comment was added by 90.152.14.231 (talk

) 16:45, 25 April 2007 (UTC).

Or 5.03 earth masses, if there are three planets, according to Udry et al.. If, as is being assumed, its radius is one and a half times Earth, its surface gravity is about 5/1.5², which is slightly over 2. Any source which says otherwise is unreliable, denying either Newtonian gravity or simple mathematics. Septentrionalis PMAnderson 16:48, 25 April 2007 (UTC)

It would be nice to have an article explaining the exact relation between mass, volume and surface gravity. I was puzzled hearing on the news that the new world could have five times the mass but only twice the gravity. I don't doubt you are right, but a detailed explaination that was accessible to non-physicisists would be useful. --GwydionM 17:12, 25 April 2007 (UTC)

Surface gravity. mdf 17:15, 25 April 2007 (UTC)

The Surface gravity page is kind of layman-opaque. Loosely: mass is (assuming constant density) proportional to volume. Volume is proportional to radius cubed. Gravity is proportional to mass, but inversely proportional to distance squared. For surface gravity, distance from the center of mass is radius. Kaleja 19:54, 25 April 2007 (UTC)

2.2 Gs is actually 220% of Earth's gravity, or 120% more again than Earth's gravity. But what I'm wondering is, if they aren't even sure about the composition of the planet (rocky or watery), how can they know what the gravity is? Surface gravity depends greatly on radius as well as mass. If the composition is really still a matter of debate, assigning such a precise value to the gravity might not be very sensible. - green_meklar 17:26, 25 April 2007 (UTC)

Rocky vs. watery describes only what's on the very top layer. The rest of it is going to be rocky, and most likely in a relatively narrow range of density. Kaleja 19:37, 25 April 2007 (UTC)

To clarify: if it turned out to be a very dense body and exactly the same size as Earth, would the surface gravity be five times that of Earth? Or if its density was very low and the radius much greater, it could have the same gravity as Earth, even a lower gravity?

I checked the article Surface gravity. It looks like it was written by physicists, whereas this Wikipedia is meant to be for everyone. If someone could add a popular explanation, that would be a useful addition.--GwydionM 16:56, 26 April 2007 (UTC)

The surface gravity of a spherically symmetric body is proportional to its mass divided by the square of its radius. For example, if a planet has mass 5 times the Earth's and radius 1.5 times the Earth's, you take 5 and divide by the square of 1.5, and get 20/9, so the surface gravity is roughly 20/9 = 2.222 times that of the Earth. Much more significantly, for habitibility, though, the escape velocity is proportional the square root of the mass divided by the radius. That same planet's escape velocity would be computed by taking 5, dividing by 1.5, then taking the square root, which gives you 1.82... multiply that by the escape velocity of the Earth, and you get approximately 20.5 km/sec, which is almost as much as Uranus'. Uranus can hold hydrogen, while the Earth cannot. That fact prevented the Earth from accumulating a gas-giant type atmosphere, assuming hydrogen was available. What about

Gliese 581 c? I just don't know. Maybe one of the planetary experts whose been editing this page can given a more informed opinion. Vegasprof

19:20, 29 April 2007 (UTC)

I think the 2nd paragraph under "Orbital" is wrong - there should be no significant difference in free fall acceleration on either side of the planet, because it moves freely around the star. Please correct me if I'm wrong, or otherwise put a link or more detail to the "simple calculation" yielding the 0.68m/sec^2 difference. Pseudopanax 23:40, 26 April 2007 (UTC)

It is removed. Temur 20:22, 28 April 2007 (UTC)

So, right now the article says "Under the assumption that it is a rocky planet, rather than an icy planet, Gliese 581 c has a radius 50% larger than that of Earth[4]. Gravity on such a planet's surface would be approximately 2.1 times as strong as on Earth.[5] If it has approximately the same density as Earth, its radius would be 1.7 times as big as that of Earth, and gravity there would be also 1.7 times as strong as on Earth." There are two estimates of surface gravity in that paragraph: 2.1 g and 1.7 g. Which is correct? 71.201.66.22 05:23, 27 April 2007 (UTC)

1.7 is just an estimation assuming that the planet is uniformly as dense as Earth's average. 1.5 seems to be calculated by a more sophisticated model, taking into account different layers of the planet and so on, but still assuming that it is similar to Earth. I deleted the sentence about 1.7. Temur 07:00, 27 April 2007 (UTC)

The gravity depends on the composition of the planet, which depends on the location at which the planet formed. I recommend a reading of this paper http://arxiv.org/abs/0704.3454v1 by Valencia and Sasselov; they have given data for a wide range of different compositions, and refer to a five-Earth-mass world, just like Gliese 581 c. Basically, if the planet formed in the inner system, it would be rocky, with a radius of 1.5xEarth, and a gravity of 2.2 gees. If however it formed in the outer system beyond the snowline, then migrated inwards, it could be mostly water, and have a radius of 2xEarths and a gravity of 1.2 gees. There is no way of telling the difference yet (unless you know different).87.102.28.2 13:46, 28 April 2007 (UTC)Eburacum

You are full right but a thing, the gravity depends only on the mass and radius, and radius is what depends on the composition. And of course, all these things are mere theoretical, maybe such planet could be a 3x or 10x Earth radius or what you want, we don't know at all. We are only sure of its mass.212.51.52.7 11:25, 29 April 2007 (UTC)

No, we're not. Vegasprof 19:20, 29 April 2007 (UTC)

I do not think that radius has anything to do with the gravity, if it did, than neutron stars would be proportionally larger than they are. Density of the object is far more important. Not knowing how dense the object is, we can only assume the mass of the object. Lets just assume new planet is 20 000km in diameter, but has density of 4, than it would be poses gravity only slightly larger than that of Earth we are talking 1.36-1.37G, if density is lightly higher, say that rocky world like earth, than yes gravity will be lot larger, depending what is made of, and if core is iron, assuming it is, than Gravity of the new planet at best would be in region of 1.57-1.6G. Even if we decide to move there some day, considering I weigh only 70kg on new planet I'd weigh between 95 and 110kg, there gos my diet plan, lol. PS consider the fact that Jupiter has diameter if 11 earths, but surface gravity is only 2.34 times that of earth. Mic of orion

How can the radius and the mass of the planet be known, yet not its mean surface gravity? If its mass is 5 times that of Earth and its radius is 1,5 times that of Earth, shouldn't this be

${\displaystyle g=GM/r^{2}=32,8m/s^{2}=3,34g}$?

Well, we technically do not really know nor the mass (the minimum mass is about 5.03 Earths but... see discussion above) nor the radius (even if we can infer it by planetary theory), so the gravity is most uncertain. Estimates I have read range from 2 to 4 g, but they are not that much meaningful. --Cyclopia 13:06, 4 June 2007 (UTC)

Your math is off. For 5 M(E) and a radius of 1.5 R(E) you'll get 2.2g (2.2 times Earth's gravity). If the radius is larger than 1.5 times (assuming it has a large outer hydrosphere (ice or water) of a couple of thousand kilometers deep) the gravity drops accordingly. The article of course mentions this and states the 2.2g for a rocky planet and more than 1.25g for an icy/watery planet. Themanwithoutapast 21:10, 4 June 2007 (UTC)

Actually surface gravity is only 1.6, and I think it might be even less, Planet is not as dense as earth, it is more similar to Mars than earth in its composition.

How do you know the density? --Cyclopia 08:07, 19 June 2007 (UTC)

Um yeah... how is it you have an exact number?--Marhawkman 18:52, 19 June 2007 (UTC)

But there might be some great candidates for earth like Moons and planets orbiting few prospecting stars. NASA and ESA are studying (observing) right now about 170 stars with potential.

Escape Velocity

It is commonly believed that the

Should we really have speculative quantities such as radius, temperature, surface gravity and density in the infobox? While the minimum mass comes from measured quantities, these figures require assumptions about the planet's composition and structure that have no observational basis. Such values should thus be taken with a strong pinch of salt, and given that values in an infobox are isolated from the discussion in the article (where any assumptions and an idea of just how speculative such values are can be discussed), this could potentially lead to confusion. I would contend that such values should be removed from the infobox and left as either question marks or do something like "see text" and give a link to the point in the article where this is discussed. Chaos syndrome 00:59, 20 June 2007 (UTC)

For radius, surface gravity and density, something like "(min probable value-max probable value)??" + link in the text could be okay, it gives the ranges supported by mainstream scientific theory but clearly states that it is an unknown. For temperature, I agree to remove. --Cyclopia 09:16, 20 June 2007 (UTC)

Given that the true mass of the planet is unknown (we only have a lower limit from radial velocities), the radius/gravity/density values, which depend not only on the unknown true mass, but also on the totally unknown composition, are totally up in the air. In fact, despite the fact that it almost certainly does not correspond to actual conditions on the planet, the equilibrium temperature calculation is probably a more robust value than the other values such as radius/gravity/density: while the (unknown) radius of the planet appears in the derivation of this quantity, it turns out that for a spherical planet (a reasonable assumption), it cancels out, leaving only a dependency on stellar luminosity and planet distance, which can be derived from measured quantities! Nevertheless, my instinct would be to leave it out, as it is a very misleading quantity for planets with atmospheres. I'd say that we should not try and avoid the fact that many of the seemingly basic properties of this exoplanet are unknown, and remove the values from the infobox. Chaos syndrome 02:15, 21 June 2007 (UTC)

But there are serious and scientific assumptions that give reasonable, although wide, ranges for mass, composition and density. I agree about being on the "safe side", but giving some range (expliciting the assumptions on which those ranges are calculated) can be informative nonetheless. We know it cannot be much denser than osmium and much lighter than hydrogen. Also the fact that the planet is now known to not transit should place some constrain on the orbital plane inclination: is there any reference about it? --Cyclopia 10:32, 21 June 2007 (UTC)

The nondetection of transits raises the minimum mass value by a small value (from geometrical considerations, I estimate an increase of around 0.02%, which is much less than the error on the minimum mass of the planet, so in fact it is such a weak constraint it can be effectively ignored). My point is not that we should remove these quantities from the article, but just from the infobox, which does not lend itself to discussions of how speculative figures such as radius are arrived at. The infobox should, I feel, reflect that the quantities are unknown. Chaos syndrome 15:59, 22 June 2007 (UTC)

Eccentricity

The table on the Gliese 581 page gives a very high eccentricity of 0.3 for c's orbit; this page gives eccentricity 0. Eccentricity 0.3 for a semimajor axis 0x 0.073 AU puts perihelion at about 0.039 AU if I got my math right; this is inside the orbit of Gliese 581 b, so I'm guessing that this page is more right than the other. Anyone have more info? Kaleja 18:14, 25 April 2007 (UTC)

Read the paper by Udry et. al.; there are at least two possible solutions for the orbit, one with two planets, one with three. IIRC The three planet solution does not determine the eccentricity, but fits the observations better; presumably 0.3 is the maximum possible eccentricity, and may include a lock between the two planets. Septentrionalis PMAnderson 18:58, 25 April 2007 (UTC)

That was me, see my comment above on the errors in eccentricity and mass. I made the edit in the Gl 581 article and indicated the eccentricity was .3. Guess I misread the paper by Udry et. al. I guess in both cases we should show eccentrivity as unknown? If .3 is wrong, 0 is wrong too. Implying the orbit is perfectly cicular (0 eccentricity) is an important error. Rich.lewis 21:13, 25 April 2007 (UTC)

Septentrionalis is correct: the paper itself says that, for a three planet model, the eccentricity is unconstrained (for two planets, it simply says it is "low"). A value of 0.3 isn't mentioned anywhere though; and where the bizarrely accurate value currently in the article (0.16±0.07) comes from I've no idea. Unless this has been stated somewhere other than Udry et al.'s paper, I suggest we settle for "unknown" (or whatever is usually used in cases like this). Spiral Wave 23:47, 26 April 2007 (UTC)

Addendum: the version of the Letter currently on Udry's homespace differs from the previously available version, hence the confusion. It seems the currently given value is as good as any till it all settles down. Spiral Wave 01:03, 27 April 2007 (UTC)

I added the 0.16±0.07 to match the Gl 581 "main" page. "Xyzzy n" added it there with the comment "changing planet data to match Udry et al." but I don't see 0.16±0.07 in the Udry et al. paper. I'm not sure if that is accurate, but at least both pages match now. The exoplanet database shows eccentricity of 0, but that probably just means it is unknown. Maybe it is better to indicate eccentricty is unknown on both pages (here and Gl 581 "main" page)? Rich.lewis 01:31, 27 April 2007 (UTC)

The new value (0.16±0.07) is given in table 1 of the revised Letter - at least, I assume Udry's webpage would carry the newer version. But the justification is minimal and it seems quite a change to make from "unconstrained". Perhaps we could leave the current value but add a footnote explaining the uncertainty? Spiral Wave 09:02, 27 April 2007 (UTC)

I found this figure cited on exoplanets encyclopedia [6]. I added the citation, I think that is good enough. They cite the original source if someone wants to dig deeper and figure that out, but you need a subscrition to get to it I think. Rich.lewis 16:35, 27 April 2007 (UTC)

The exoplanets encyclopedia has updated sometime today with that new value; it still said zero yesterday. So there's no more digging to be done; everything agrees. I guess if it's good enough for the EE it should be good enough for us! Spiral Wave 17:31, 27 April 2007 (UTC)

Inclination

I decided to immediately revert the last two changes that claim that the orbit is inclined 84 degrees to our line of sight, i.e., close to edge on. No citation is given, and I don't believe it's known. The reason I'm reverting immediately, instead of waiting a week or so, is that I want to decrease the number of innocent readers who get fooled; we have to realize that this page is likely read frequently by schoolchildren, etc. Of course, if there is a citation to this, please find it, and revert back, with the citation. Vegasprof 11:15, 1 June 2007 (UTC)

4.3 Possibility of Eclipsing from 581b

Now I'm no scientist but I have a hunch that based on the small size of the Star and 581b being between 14 to 15 times bigger than 581c and the fact that the orbit times only take 5 and 13 minutes respectively is it possible that 581b could eclipse light from 581c on a reccuring basis? I was hoping to try and figure this out but I can't find any such information about distance to the star? can anyone help confirm or deny this? —The preceding

You mean orbit times of 5 and 13 days, not minutes. That 581b at any time within the next years eclipses light from 581c (you mean an eclipse in the sense that we don't see it) is rather unlikely given the distances between them. In any event, with current means neither 581b nor 581c can be observed directly anyway. Themanwithoutapast 09:49, 26 April 2007 (UTC)

The Wikipedia article on transits explains:

"The word "transit" refers to cases where the nearer object appears considerably smaller in apparent size than the more distant object. Cases where the nearer object appears larger and completely hides the more distant object are known as occultations. Cases where one object moves into the shadow of another are known as eclipses. Each of these three terms are the visible effects of a syzygy."

Thus, to an observer on

Gliese 581 b would be easily visible to the naked eye as a large black dot moving across the face of the sun (which would appear more than 5 times the diameter of the Sun from the Earth, although dimmer). If the two planets' orbits are in the same plane, a transit will occur every 9 days, approximately. Vegasprof

10:35, 26 April 2007 (UTC)

Correct Vegasprof, transits would occur rather often for observers on Gliese 581 c. I however assumed the question was directed towards transits to be detected by us from our solar system - maybe I was thinking to complicated. Themanwithoutapast 11:55, 26 April 2007 (UTC)

The article states both that the planet is not known to transit, and that a team is planning on observing it as it passes in front of the star. That's a rather glaring inconsistency. Riedquat 12:53, 26 April 2007 (UTC)

they're probably trying to figure out whether or not it does.--Marhawkman 01:30, 11 May 2007 (UTC)

Not Known To Transit - Source?

Currently, under "Liquid Water," the article reads:

Techniques such as the one used to measure

If a citation is needed for the star's orbital period, then put the fact tag where it belongs. If the citation is needed to establish the potential application of the technique to Gliese 581 c, then move the "cite needed" to the middle of the sentence so its purpose is clear. If a cite is really needed establishing that we don't know if the star transits, then cite the original press release (which establishes that), and refrain from cluttering the article with an ugly "cite needed" tag. Can we agree? (I won't further revert, BTW - it's your ball game.) Jeff Medkeff | Talk

Sorry about the fast revert - you're right. What needs a cite is that the method requires it to pass directly in front of its star. So:

...but this method requires the rare coincidence of a planet whose orbit causes it to transit directly in front of its star,^{[citation needed]} something Gliese 581 c is not known to do.

Would that be more reasonable (per Jeffmedkeff)? My original location for the citation was based on an assumption on my part. Esseh 15:56, 26 April 2007 (UTC)

Well, I mean that examining if this thing is transiting should be relatively easy. As it's orbital period is around 13 days, it should transit once in every 13 days- just if it orbits in the right plane.Regular observations should determine this. But my concern is about another thing. As I read before, the planet was discovered by measuring the radial velocity of the parent star. The problem is, that this method doesn't give us answer about planets radius, mass or even it's distance from the star- just minimum possible mass. So we cannot be so happy, we don't know almost anything, but everybody is happy- "we discovered first planet similar to Earth in habitable zone" etc. But I ask, are we sure of that fact? Amakthea computer 17:42, 28 April 2007 (UTC)

Inclination not yet known

The 5.1 Mass-Earth value actually reflects the value m sin i, not merely m. The inclination i of the planet's orbit is as yet unknown (as it is for most extrasolar planets), and therefore 5.1 Earth masses reflects the minimum mass of Gl 581 c, not necessarily its actual mass. If its orbit is exactly edge-on to us then this will also be equal to its actual mass, but in reality its mass could be larger. The Doppler detection method alone is not capable of discerning the angle of inclination of a planet's orbit and perhaps the main page should be edited to reflect that we are really talking about m sin i for now. Bolthus 02:51, 27 April 2007 (UTC)

This is a very important point. The article needs a major revision to reflect this. Article perhaps is assuming dynamical mass determinations such as done for GJ 876 (Rivera et al. 2005). Unexpect 03:35, 27 April 2007 (UTC)

Philip, perhaps you can check this out. The preprint clearly states in the abstract that the mass is approximately 5 times Earth, but the table gives the minimum mass, i.e., mass*sin(i). Assuming random orientation of the plane of the orbit, the expected value of sin(i) is pi/4, roughly 0.785. The median value of sin(i) is sqrt(3)/2, approximately 0.866. This means that if the minimum mass is 5.03, the probability is one-half that the true mass is above 5.8, unless there are other data constraining i. (Note: I have made a hidden assumption about the a priori distribution of masses of planets, but since no one knows that distribution, I can get away with it.) BTW, the quote in the Rivera paper is (if I am not mistaken), "Note that mutual perturbations among the planets depend on actual planetary masses rather than the product Mpl sin i, and such perturbations may thus be employed to place bounds on sin i," If such an analysis is mentioned in the Gliese 581 paper, I missed it. Vegasprof 12:23, 27 April 2007 (UTC)

I agree with everything you just wrote. If there were a concise way to explain this in the wikipedia article, it would be vastly improved. Unexpect 16:00, 27 April 2007 (UTC)

The statistics above is altered by a significant detection bias. Since the RV variations of planets are at the lower detectable end, we are at the moment very much biased towards detecting the high sin i cases, but the estimates with random inclination axes are valid only in complete samples. The situation is, therefore, not quite as bad. --201.215.225.95 01:09, 29 April 2007 (UTC)

I'm sure the bias exists, but can't actually be that significant. Otherwise a much greater fraction of the radial velocity discovered planets would have been found to transit. Unexpect 02:22, 7 May 2007 (UTC)

Temperature

The article states that the temperature is −3°C–40 °C, does this mean -3 to -40, or -3 to 40?--Rhydd Meddwl 18:46, 26 April 2007 (UTC)

It's −3 to 40.

BlueEarth

19:51, 26 April 2007 (UTC)

"equilibrium surface temperature" - i'm not a scientist, i don't know what it is, and i suppose, i'm not the only one :) there is no explanation for "equilibrium" @ wikipedia, perhaps someone who knows about it, should write few lines about equilibrium and link to this page.

What's the temperature formula? Wouldn't be (L_star/L_sun)^1/3.5 × 256 ÷ a^0.5). 75.57.104.48 02:31, 18 May 2007 (UTC)

I would like to confirm/vindicate Glycerinester's calculations on the heat received by Gliese 581 c
through a slightly different scientific method that I have not seen expounded on here. I found these two formulas for Luminosity,
L=4pi*(R²)*a*(T⁴), L=4pi*(Dv²)*fv
noticed they had the same result for the Sun and Earth (3.8525 E26 Watts),
put them together, and rearranged them algebraically to get the insolation (flux) for any planet at any distance.

(R²)*a*(T⁴)=(Dv²)*fv

L= luminosity (Watts)
R= Star Radius (Sol)
T= Star photosphere temperature (Sol)
a= Stefan-Boltzmann constant (5.6703e-8)
e= eccentricity
Dv= Average distance (semi-major axis), AUs
Da= Aphastron distance (Dv+(Dv*e))
Dp= Periastron distance (Dv-(Dv*e))
fv= Average Flux (solar constant)
fa= Apastron Flux, Watts per square meter.
fp= Periastron Flux
AU, 149597876600 meters (~Mariner 10)
example:
fv(earth)=((696000000²)*(5.6703e-8)*(5780⁴))/(149597876600²)= 1,369.888 W/m²

Incidentally, that is the flux for Earth mesured by satellites, or solar constant.

fa= (((R*696000000)²)*((5.6703e-8)*((5780*T)⁴)))/(((Dv+(Dv*e))*149597876600)²)

fv= (((R*696000000)²)*((5.6703e-8)*((5780*T)⁴)))/(((Dv*149597876600)²)

fp= (((R*696000000)²)*((5.6703e-8)*((5780*T)⁴)))/(((Dv-(Dv*e))*149597876600)²)

                Periastron    Average        Apastron  
                Flux (W/m<sup>2</sup>)  Flux (W/m<sup>2</sup>)   Flux (W/m<sup>2</sup>)  
 Gliese 581 d      464.24        297.11         206.33  
Mars               718.54        590.59         494.00  
Earth            1,416.84      1,369.888      1,325.23 
Venus            2,656.65      2,620.65       2,585.37 
 Gliese 581 c    6,912.915     4,877.753      3,624.965
Mercury         14,494.998     9,146.671      6,292.663 
 Gliese 581 b   11,502.254    11,046.765     10,617.806 
   
               % of Earth's    % of Earth's    % of Earth's      Flux %
               Average Flux    Average Flux    Average Flux      range diff. 
 Gliese 581 d      33.89%         21.69%          15.06%           18.83%
Mars               52.45%         43.11%          36.06%           16.39%
Earth             103.43%        100.00%          96.74%            6.69%
Venus             193.93%        191.30%         188.73% [4]        5.20% 
 Gliese 581 c     504.62% [2]    356.07% [1]     264.61%          171.47% 
Mercury          1058.12%        667.69%         459.36%          598.76% 
 Gliese 581 b     806.40%        839.65%         775.09%           31.31% 
      
                   Ecc.         Ecc.       Period       Period      period (years) x 
                            (% of Earth)   (days)       (years)     flux % range [3]
 Gliese 581 d      0.2       1196.87%       83.6         0.229        4.31%
Mars               0.0934     558.94%      686.98        1.881       30.83%
Earth              0.0167     100.00%      365.26        1.000        6.69%
Venus              0.0068      40.69%      244.7         0.670        3.49%
 Gliese 581 c      0.16       957.50%       12.932       0.035        6.07%
Mercury            0.2056    1230.57%       87.97        0.241      144.21%
 Gliese 581 b      0.02       119.69%       5.3683       0.015        0.46%

[1] Originally I would have said I concur that 2.54 is the average, but after redoing the calculations with the Wikipedia data on the star (rather than Exoplanet.eu) I would have to say this planet get's 504.62% times the heat Earth does at Periastron, using the median eccentricty. If you assume the maximum eccentricity, 0.23, then it's 600.5% - Imagine Miami, Florida with a low of roughly 120°C/248°F. As long as experts are allowed their agenda (publicity=funding) we aren't going to have accurate knowledge here.

[2] Water disassociates into oxygen and hydrogen at 374°C. Regardless of emissivity, the likelyhood of this planet having water is far far less than that of Venus given calculatable heat and minimum mass. I concomitantly recommend the removal of all (ad nauseam) reference to water (no pun intended) for this planet.

[3] for anyone who wants to argue that (for heat) the eccentricity doesn't matter if the period is short.

[4] I think it's deceptive to refer to the albedo of Venus and ignore the same 96.515% greenhouse-gas-atmosphere that makes it so. Also, though I do appreciate the sarcasm of Esseh's argument on habitable zones I'd have to say that although the logic is valid, the statements in it are false. That's a big "if" with Pluto being habitable, because for that kind of internal core temperature heating it would have to have a mass more like one of the gas giants, so then it is the pressure that would make it uninhabitable/inhospitable.

(NASA says Jupiter's core is 30,000°C, yet the exosphere is -124°C.)

Also, with Venus anything that was so reflective, with the level of heat that Venus recieves it would not have the stability to remain so, and that cycle would collapse. Conversely, you need a minumum 3000°K to disassociate the greenhouse gas CO₂.

Generally, Although I would be the last one to defend the current monodimensional habitable (residential/commercial) zone definitions, I have to disagree and say that with all accounted for dimensions that a habitable "Zone" is definable. (atomic abundance, albedo, emissivity, axial tilt, distance, heat, pressure, Gravity, Density, etc.) Definitions are major part of what science is about. Habitable Albedo range, Habitable emissivity range, Habitable pressure from mass range, etc. (Incidentally, Ice melts at -3°C under pressure, and has enough energy to break cohesion at 26°C, which makes 0°C to 100°C a nonsense range. No really, 100°C - a steam planet, and so it must be habitable - Not for me.)

I invision a habitable zone definition where the other dimensions shift with the planet mass being considered, the way the current one shifts with the star mass, the mass of the planet being the second dimension in line of importance (star mass first) because it impacts on so many of the other factors. Someone might comment that's like going back to a geocentric perspective, but it's not the star's habitiability that we are looking at.

Incidentally, "Super-Earth" is deceptive, it should be "Super-Terrestrial."

GabrielVelasquez (talk) 02:34, 23 December 2007 (UTC)

Derivation

Most of the section entitled "Derviation" (specifically, up to and including "..equating the two quantites") doesn't seem to be specific to Gliese 581 c. Would it make sense to move it to a more general article such as Planet? Mattmm 13:04, 18 October 2007 (UTC)

I entirely agree. Planetary habitability seems like the best article to move this part to. Kevin Nelson (talk) 08:14, 20 November 2007 (UTC)

Ecosphere

I have removed this word from the intro as a likely neologism (no relevant hits at google found). If any are found later, feel free to re-add it, though I find the current wording concise. mdf 15:46, 25 April 2007 (UTC)

It is a valid term and not a neologism. However, "habitable zone" is normally used instead, so we should stick on it.— JyriL ^talk 16:13, 25 April 2007 (UTC)

I know it is a valid term: google has many references to the concept. (Note that in these cases it is not an actual, physically defined, sphere being referred to, but a space, and more a parameter space than anything else.) The central issue is whether there is any non-trival amount of astronomical literature that uses the word in the sense this article did. I now see that the ecosphere disambiguation repeats the use that was here, and even habitable zone does likewise. None with any supporting references. mdf 16:34, 25 April 2007 (UTC)

My dictionary is telling me that it is the equivalent to the biosphere. Chris Buttigieg 16:45, 25 April 2007 (UTC)

Life on it

One thing which i found a little wierd is, are they talking about life on it or us living on it. Water by NO means is an ingredient for living. Some alien might need light to live instead, so i think we need to specify that, also, how is this discovery in any importance to us? If it had some nice beaches and good 5 star hotel resorts i might just care, its just another rock out there. —The preceding

Both. At any rate, I don't think we need to qualify the possibility of life with mentions of exotic life that doesn't need water, or any of the very long list of stuff that life potentially does not need. The best solution is to use the phrase "life as we know it," but even the "as we know it" bit is implied in any astronomical paper. Egumtow 19:51, 25 April 2007 (UTC)

All known life needs water, and there are serious arguments that water is necessary for the development of life. (non-runaway chemical reactions are far faster in liquids than gasses or solids, and water is a common, excellent solvent whose polarity is fundamental in the resilient structures of life. Also, arguing a priori, if there are several different forms of life, ie water-based and x-based, they are probably not equally likely - since we exist, we can expect that any other form is relatively improbable.) --72.252.40.68 22:16, 25 April 2007 (UTC)

I made this edit. More accurate IMO.

heru|nar

12:17, 26 April 2007 (UTC)

Water is NOT essential to life. H2S can produce sugars in plants just as well as H2O. The byproduct however, using H2S as an electron source rather than H2O, is S2. Sulfur gas. Read up on your evolutionary biology people... —The preceding

unsigned comment was added by 128.205.59.183 (talk

) 19:17, 26 April 2007 (UTC).

I think this discussion might benefit from a post I just made on Talk:Astrobiology. I won't repeat it here, but it's germane. Esseh 01:14, 27 April 2007 (UTC)

Habitable Zone

(moved down from above) Let me get this right, Gliese 581 c orbits Gliese 581 at 11 million kilometer orbit is that correct assumption (so says some here)? if so, I'd say Gliese 581C perhpas is not in habitable zone, as Gliese 581 has diameter of 530 000km.

I'd say more likely the habitable zone would be in region of 20-25 million from the parent star. It is a Red Dwarf star true, but it is also quite big for red dwarf star more of a K star magnitude than red dwarf, well, K stars start at 700 000km diameter or 0.5 mass of Sun, red dwarfs anything it seems from 100-600 000km or 0.1 to 0.45 mass of our sun, since this red dwarf is quite large, I' extrapolated some numbers and came with the figure of 20-25 million kilometer for best habitable zone, just my thoughts. Mic of Orion

The team that made the discovery of Gliese 581 c and d describe c to be "on the warm edge of the habitable zone" and d to be "on the cold edge of the habitable zone. We can therefore interfere that Udry and his team define habitable zone for Gliese 581 to be from about 0.07 AU to 0.25 AU or about 10 million to about 40 million kms. How someone defines "habitable zone" is up to him, however the most common definition would be "liquid water on the surface of that planet possible" - while albedo, atmosphere etc. of Gliese 581 c and d are unknown, just calculating their possible mean black-body temperatures they may fall into the liquid water on the surface variety of planets. Themanwithoutapast 11:28, 25 May 2007 (UTC)

Most people here might agree with Mic, that Gliese 581 c is probably, for many reasons, pretty damn hot to be habitable, but exploring this example illustrates that really any object could be any temperature. High enough albedo and anything freezes, high enough greenhouse effect and it boils. Habitable schmabitable. Glycerinester 06:28, 26 May 2007 (UTC)

I have to insist, as I will elsewhere more appropriate as well, that anyone using the term "Habitable" or "Habitable Zone" preface this with whether they are refering to ET life (including Bacteria) able to withstand absurdly extreme

GabrielVelasquez (talk) 19:24, 29 December 2007 (UTC)

Analysis shows this planet may not be habitable (von Bloh et al. (2007))

See this paper [7], where a more detailed analysis of the habitability of the outer two planets of the Gliese 581 system is done. The result: Gliese 581 c is too close to its star to be habitable. On the other hand, Gliese 581 d may be able to support liquid water. Chaos syndrome 18:57, 29 May 2007 (UTC)

"...not habitable" versus "...may have liquid water." Why would one look into such self-contradictory reasoning; what would one expect from Chaos.

I have to insist, as I will elsewhere more appropriate as well, that anyone using the term "Habitable" or "Habitable Zone" preface this with whether they are refering to ET life (including Bacteria) able to withstand absurdly extreme

GabrielVelasquez (talk) 19:36, 29 December 2007 (UTC)

Interesting that you misquote the user in question and then use an ad hominem based on their handle. Where's the self-contradiction? You are aware that a large part of the discussion of planetary habitability is based on determining the possibility of the existence of liquid water... 131.111.8.104 (talk) 00:53, 21 February 2008 (UTC)

He wasn't bothering with logic, moron, that's above the discussion level of most here, stupid, that's just sarcasm... —Preceding unsigned comment added by 198.163.53.10 (talk) 21:13, 22 February 2008 (UTC)

Problems with analysis of von Bloh et al. (2007)

The analysis presented in by von Bloh et al. (2007) is detailed, but is based on a number of assumptions that may not be warranted. One of their foremost assumptions is that a silicate-carbonate cycle on Gliese 581c operates in much the same way as it does on Earth. This is a significant assumption, as the terrestrial silicate-carbonate cycle is largely predicated on the ubiquity of pelagic photosynthesis accompanied by calcite/aragonite deposition. One problem with this assumption for Gliese 581c (aside from the obvious assumption that life exists at all) is the underlying assumption that primary productivity is necessarily accompanied by CaCO3 formation. The star Gliese 581 is a low-metallicity star (M/H = -0.33 dex), and should therefore have a fairly low crustal abundance of Ca. Under such conditions the evolution of organisms relying on formation of calcium carbonate tests is unlikely. Low crust/mantle abundances of Period 4 elements (e.g. Ca, Fe) would tend to produce highly silicic crustal rocks (e.g. granite, granodiorite), the weathering of which would produce a much lower flux of dissolved Ca to oceans than is normal for Earth. Crustal Mg concentrations on Gliese 581c would be more similar to solar Mg/Si values, and thus biological magnesite (MgCO3) formation is possible, but probably should not be assumed.

Without a large scale flux of atmospheric CO2 to the crust via carbonate biomineralization, a conventional silicate-carbonate cycle would not be supported. Benthic storage of dead organic matter would presumably occur in any event, assuming the presence of marine photosynthesizers, and could sustain a more limited C cycle based on tectonic return of sedimentary C to the atmosphere. However, that still assumes conventional subduction-related tectonic processes.

In addition, it is probably not realistic to assume a terrestrial geodynamo for Gliese 581c, which likely contains a much lower absolute abundance of Fe and therefore may have a very small Fe/Ni core. If the planet wandered in from a more distant formation orbit, its core Fe content would be even smaller (though its volatile content would be significant, in that case). Gliese 581c is likely to have an ample geothermal heat engine, due to what is likely to be a mantle abundance of K similar to our terrestrial planets, and also due to its larger bulk and therefore larger insulating capacity. So Gliese 581 is likely to have active mantle convection, which coupled to abundant H2O would argue for active plate tectonics, however probably without a strong geomagnetic field.

In short, the von Bloh (2007) paper is intriguing, but depends too heavily on the assumption of planetary parameters that are either unlikely or unsupported by expectations based on cosmochemistry and biogeochemistry. --Nimwe 22:17, 30 May 2007 (UTC)

Manfred Cuntz is an associate professor of physics (specialty astronomy) at U Texas Arlington. The other three co-authors, including von Bloh, are from the the Potsdam Insitute for Climate Impact Research (PIK). Vegasprof 00:54, 31 May 2007 (UTC)

Understood. Please see Nimwe user profile: contributor is an associate professor of geochemistry (specialty: global biogeochemical cycling processes, planetary geochemistry). --Nimwe 03:28, 31 May 2007 (UTC)

Luckily for us, Wikipedia's requirement of verifiable sources means we don't have to worry about the personal credentials of contributors. Is there a published rebuttal to this paper? Debivort 03:50, 31 May 2007 (UTC)

Thanks, Nimwe, for putting up your user page. After I saw your long comment here, I tried to check on your credentials, and there was nothing there ... that was yesterday, I believe. Anyway, my point is that

Udry et all stated unequivocally that Gliese 581c is in the habitable zone of Gliese 581

, while von Bloh et al, rebut that (although they don't use the word "habitable zone.") I did notice at the time that the insolation on Gliese 581c is greater than on Venus, but the supposed definition of "habitable zone" is as broad as possible, i.e., not so that every planet in it is habitable, but that every habitable planet is in it. (Note: the title of their paper was changed after about 2 days; the phrase "Habitable Planet" was removed. All they claimed, basically, was that they had no proof that it was not habitable.)

I could not find any published rebuttal to the von Bloh, et al, paper; but this is not surprising since it just appeared, and is not yet peer-reviewed. But let's be honest: climate modelers do not have a very good track record of modeling climate on the Earth, where we have better data than for Gliese 581 c. That means that published models of climate on worlds of unknown mass, chemistry, etc., even if published in peer-reviewed journals, are fascinating reading, but should be read with a healthy dose of skepticism, and it is perfectly reasonable, in my opinion, to cite the von Bloh article, while pointing out defects of their model, such as noted by Nimwe. Vegasprof 07:47, 31 May 2007 (UTC)

Looks also like the case being discussed is for the planet being terrestrial. However, if the information from Gliese 436 b is of any relevance, the planets of Gliese 581 may be mainly icy, which would yield a rather different chemical environment. If there is enough ice, you'd end up with high-pressure ice above the silicate core. You'd presumably end up with an H₂O-rich, rather than CO₂ rich atmosphere (IIRC water vapour is far better greenhouse gas than carbon dioxide, but I'm not sure how the red dwarf spectrum would modify this). However, the article does mention that the planet receives more radiation than Venus, which bodes ill for habitability I would think. Chaos syndrome 07:56, 31 May 2007 (UTC)

It's a good point that Gliese 581c would receive a greater solar flux than Venus, but that is not necessarily a limit on habitability. I teach courses on the geochemistry of planets and their surface environments, and the Venus/Earth example is a very illustrative one to teach the sensitivity of initial conditions. A leading hypothesis for why Venus and Earth ended up so differently, despite having broadly similar compositions and starting conditions as Earth, is that Venus probably received just enough insolation at its distance from the Sun to prevent initial condensation of oceans. Without oceans there could be no practical storage of C as a mineral (by dissolution of atmospheric CO2 in ocean water, followed by at least chemical precipitation of CaCO3), so Venus became a victim of a runaway greenhouse effect. Lack of oceans also likely contributed to Venus having no plate tectonics, because of the melting-point depression effect of interstitial water on crust/mantle silicates. On Venus, H2O stayed in the atmosphere and was ultimately lost to space via photolytic decomposition to H2 and O•. The H2 diffused to space, the O• oxidized volcanic SO2 to form clouds of sulfuric acid.

The point here is that small differences in initial conditions can ramify through time and lead to very different outcomes. This puts real limits on our ability to predict planetary conditions from limited data, such as we have now concerning Gliese 581c. It may be that intense solar insolation has dessicated 581c. However, the possibility of liquid water condensation and ocean formation on the nightside leaves open the potentiality of a habitable environment today; oceans allow for long term carbon storage, which could mitigate a runaway greenhouse. The likely paucity of Ca on 581c argues against C storage via calcite deposition, however chemical deposition of MgCO3 might be feasible, and if life emerged on 581c there could be other disequilibrium alterations to atmospheric chemistry and climate. At this point we just don't know enough.

Personally, I just think it's fascinating that habitability is at least possible for not only 581c, but also 581d... two planets in the same system. Red dwarf stars are very common, and as recently as the publication of Rare Earth (Ward and Brownlee), which detailed the rare earth hypothesis, red dwarf star systems were largely dismissed as potentially harboring habitable planets. --Nimwe 18:36, 31 May 2007 (UTC)

Of course by the same standards our system also gets at least two "possibly habitable" planets, one of which we happen to know didn't make it. No real reason for that to be unusual. But in orbiting a G star I guess we're relative oddballs compared to the zillions of M's. Glycerinester 03:42, 1 June 2007 (UTC)

Im very glad to have found a seemingly knowlegable comment of that paper here, however, if this paper is or gets peer reviewed, untill such rebuttals are also peer reviewed, we should mention this paper in this article. I only saw the paper in arxiv.org so I guess its not necessary to include it yet, but just wished to note how wiki policy likely forbids the inclusion of any criticism of this paper, if it is or gets peer reviewed, in this article untill such criticism passes the same test. And it would likely be a good idea to mention the paper as soon as possible; its a very interesting debate. I do hope this will remain on the talk page, though, and that such rebuttals will appear soon enough through 'proper channels' :) --83.131.133.5 23:21, 1 June 2007 (UTC)

Mentioning the paper and it's conclusions seems appropriate. Treating it as authoritative does not.--Marhawkman 00:10, 2 June 2007 (UTC)

By the same token, we probably shouldn't treat the assertions that the planet is habitable as authoritative either - going with an equilibrium temperature calculation (which has been pointed out as having severe deficiencies as an indicator of habitability) as an authoritative declaration of habitability, while we treat a paper doing detailed calculations as non-authoritative, seems a bit absurd. Given the fact that the planet receives more radiation than Venus (made in the von Bloh paper, and pointed out by several commenters here who understand basic physics principles), all claims about habitability in the article should be worded very cautiously indeed! Chaos syndrome 15:57, 2 June 2007 (UTC)

I must concur. We simply lack the evidence to say whether it is or not.--Marhawkman 22:02, 3 June 2007 (UTC)

Is this planet habitable for Humans or just for life in general?

Basically I think that life in general, could exist under extremely different circumstances, imagine life existing at several thousand degree Celsius, composed of heavy elements, or life forms existing on million degrees, composed of pure energy and magnetic relationships.

Even quite similar life to our's could live on something like 40C to 80C, while we could have a real hard time there.

What I want to say is that humans are very specialized when it comes to requirements of habitat, change anything like: temperature with more then 40degrees, gravity, luminosity, radiation level, different bacteria, lunar mass, winds, or ... (you get the point). I mean there is a whole lot of things that can be changed and we would not feel comfortable to say the least ...

So I think that a more practical solution is to build some environment that is good for us, rather then go and search a whole lot of matching combinations (consider the chaos theory, put in more then 100 variables, and search for the odd's that you find the right combination, then you'll get the picture) ... For example the space between the stars are unimaginably large, so basically we could pick any place and build this environment. \

BTW: why go out when we can go in? For example at this moment scientist did not find the smallest particle, wouldn't it be cool if an electron could hold the level of detail for a planet? Then perhaps we could even go in, not just out :)

Hope this short essay is relevant to you and perhaps even useful ;) --HappyInGeneral 18:02, 26 April 2007 (UTC)

This page is for discussion intended to improve the article, it is not a talk forum. If you are interested in interstellar colonization, research that topic on Wikipedia, do not come here. --72.252.40.68 18:42, 26 April 2007 (UTC)

Thank you for your comments, anonymous user. --NEMT 01:18, 27 April 2007 (UTC)

I would expect the primary issue would be the dramatically greater gravity on a planet lik Gliese 581 c. --NEMT 01:18, 27 April 2007 (UTC)

Thank you for you suggestions :) --HappyInGeneral 16:01, 28 April 2007 (UTC)

I have to insist, as I will elsewhere more appropriate as well, that anyone using the term "Habitable" or "Habitable Zone" preface this with whether they are refering to ET life (including Bacteria) able to withstand absurdly extreme

GabrielVelasquez (talk) 19:22, 29 December 2007 (UTC)

A little caution!

Reading the discovery paper, it would seem that the 0-40 degrees C value is an equilibrium temperature, not the surface temperature. In fact, from the paper, it appears they are using the following formula, where incident radiation on the planet is equated with the radiation of a spherical blackbody:

${\displaystyle T_{p}^{4}={\frac {L_{\ast }(1-A_{p})}{16\pi \sigma a^{2}}}}$

Where T_p is the planet temperature, L_* is the stellar luminosity, A_p is the albedo, sigma is the Stefan Boltzmann constant and a is the planet-star distance. This gives the range from -3 to 40 degrees C range in the paper (with the lower limit being for a planet as reflective as Venus). The same formula gives an equilibrium temperature for Venus of -20 degrees C, so I'd take the habitability of Gliese 581 c with a pinch of salt, since it seems to be receiving more energy than Venus does, and Venus isn't really a model of a habitable planet. Chaos syndrome 10:57, 26 April 2007 (UTC)

It meets the requirements for liquid water (as it is in the habitable zone of that solar system). That is what the paper claims, anything else is just speculation. Themanwithoutapast 11:47, 26 April 2007 (UTC)

The paper also claims a luminosity for the star of 0.013 times solar, which would put the habitable zone at 0.11 AU (basic physics - since radiation falls off as distance squared, take the square root of the luminosity to get equivalent distance for Earth insolation), outside the orbit of Gliese 581 c. Unfortunately, the temperature estimates from the paper are not helpful for assessing whether the planet is habitable - the effective temperature of Venus is -20 degrees C, the effective temperature of Earth is also about -20 degrees C, yet the surface temperatures of both planets are quite a bit higher (Venus very much so). Clearly if -20 degrees C effective temperature is observed on a planet has gone runaway greenhouse, a higher effective temperature (such as -3 degrees C as put for the lower limit of Gliese 581 c, assuming Venus-like reflectivity) means that habitability is no way guaranteed! These claims of habitability come from an extremely simplistic definition of planetary temperature, which would actually rule out Earth's habitability on the basis of it being too cold to support liquid water (bizarrely enough, same would go for Venus, since it is more reflective which seems to cancel out its increased proximity to the Sun). Unfortunately it seems no citeable source (at least that I could find) has done a proper analysis of the habitable zone (taking into account greenhouse effects of an atmosphere thick enough to support liquid water and with enough greenhouse gases to avoid freezing out on the dark side of the planet), and everyone is trumpeting these effective temperature values as if they mean habitability, when in fact they are more than high enough to trigger runaway greenhouse. So we're stuck with saying in this article that the planet is habitable, since any more detailed analysis is at present original research. Chaos syndrome 12:53, 26 April 2007 (UTC)

Yah, if this planet truely is "Earth-like" I'd believe the inverse square law far before some backwards and incomplete formula. Direct method, vs. going all the way around from the wrong end and making assumptions along the way. Odds are of it being too hot. Of course, it could be frozen on one side and baking on the other, it might not even have an atmosphere, it's atmosphere could be hundreds of times thicker than Earth, it could be volcanic, it could have oceans of acid. They're so many possibilities. We don't even know the mass that well yet. Right now no one knows the temperature. Sagittarian Milky Way 04:07, 27 April 2007 (UTC)

In fact, it looks like in a later version of the paper, the word "habitable" has been dropped from the title, and there is now an extra bit about the surface temperature (as opposed to equilibrium temperature) and greenhouse effects. Chaos syndrome 10:39, 27 April 2007 (UTC)

Bummer. Silly amateurs don't know about all this albedo and greenhouse and rotation and whatever but we know this planet gets L_Gl581/a_c² = .013/.072² = 2.44 times as much heat from Gl581 as earth gets from the sun -- which is more than Venus. Venus only gets 1.9 times as much heat as earth gets. Given the implications of the term habitable zone -- i.e., Earth in the middle by definition, Venus and Mars outside, the use of the phrase in this case is not warranted, regardless of who said it first. Glycerinester 18:29, 29 April 2007 (UTC)

In the absence of any refereed papers to the contrary, I've referred the claim about 581 c being in the HZ back to the original statement by the researchers.

"Results: The super-Earth Gl 581c is clearly outside the habitable zone, since it is too close to the star." http://arxiv.org/abs/0705.3758v3
You conveniently ignore articles to get your way.
This scientific paper is quoted all over the talkpage and is one of the references in the article.
198.163.53.10 (talk) 21:13, 12 March 2008 (UTC)

Life on this world?

Well, there's different types of life on each and every habitable planet. But this planet, although "Habitable" could hold hostile beings. We wouldn't be sure if they were hostile or not, seeing as it is MANY light years away (A single Lightyear is 5,900,000,000,000 Miles in length.) If possible, do ANY of you Wikipedians think this world could have life, like ourselves, on this planet?

This talk page is not really the place for that type of speculative discussion, it's for discussing the article so we can improve it. You might look into internet forums on astronomy, science in general, or science fiction, I'm sure there are a lot of interesting discussions going on right now on this topic with this research so fresh in the news.--Eloil 12:21, 27 April 2007 (UTC)

there's different types of life on each and every habitable planet. and you're basing this on what? --NEMT 14:18, 27 April 2007 (UTC)

Serious media mistake

An important point may have gotten lost up there at

The problem is that this isn't an ordinary wikipedia editing error, this is a mistake that's been made by professionals and we have to find corrections from reputable sources, not our own math. In any case, as much of this habitability stuff should probably be cleaned out of the article as possible, including the pretty graphics. Glycerinester 18:51, 29 April 2007 (UTC)

What Udry and his team in their letter report state is that Gliese 581 c is on the warm edge of the habitable zone and Gliese 581 d is on the cold edge. That should be said in the article. You are right that anything else is just speculation. Themanwithoutapast 19:15, 29 April 2007 (UTC)

Well, whatever they meant by it, to get the same amount of radiation in our solar system Gl581c would have to be inside Venus and Gl581d would have to be to be in the asteroid belt. Their definition of a habitable zone includes Mars and Venus. I'm not saying they're not notable sources, I'm just saying this is not what the whole rest of the world means when they use the words and we should keep an eye out for sources that figure it out. Glycerinester 19:49, 29 April 2007 (UTC)

What is meant with habitable zone is that liquid water could exist on a certain planet in such zone. We do not know the albedo of GJ 581c nor do we know if it has an atmosphere or if it has one what its composition is. With an albedo as high as Venus, GJ 581c would very well be a good candidate for liquid water, if the effects of its atmosphere are not as dramatic as on Venus (which by the way has an equilibrium temperature of -43C without its atmosphere and a greenhouse warming of 513°C compared to -17°C for Earth with a greenhouse warming of 32°C). Themanwithoutapast 20:37, 29 April 2007 (UTC)

VENUS HAS A GREENHOUSE GAS EFFECT THAT GIVES IT A 462 degree celcius average because...

The non-scientist who like to quote themselves here for the agenda of depicting this planet as habitable should know that the greenhouse gas effect that causes the greatly exaggerated temperatures of Venus to a global 462 degrees celcius average were started from the heat Venus recieves from the Sun. The simple fact of this process is in no way limited to our own Venus, but we must accept that catagorically that other solar systems will have Venus like planets and Super-Venuses. please help yourselves to the healthy pattern of thinking that is in the acceptance of this simple fact.GabrielVelasquez (talk) 06:14, 5 January 2008 (UTC)

"Results. The super-Earth Gl 581c is clearly outside the habitable zone, since it is too close to the star."
This link to this scientific paper has been both abuse and ignored: [[8]] 205.200.11.201 (talk) 05:06, 28 January 2008 (UTC)

life not water

Why do they assume the liquid there must be water, and water must be there to support life, other solvents could be present instead , such as methane, ammonia or hydrogen sulfide, see this article

http://science.howstuffworks.com/alien-physiology4.htm

Because water is the only thing humans have ever seen living things thrive in. Thats why it says it is possible for live "as we know it" to exist there. And until scientists discover something that can thrive on something other than water, water will continue to be viewed as necessary for life to exist. Thats the way science works, until it can be proved, it will remain only theory.

This is moot and/or not relevant to this article. This planet at perihelion gets 505% of the solar radiation that the Earth does, and water disassociates into Hydrogen and Oxygen at only 374°C (Venus 194% at Perihelion). There is less water on this planet than there is on Venus, which is to say, there's NONE. - GabrielVelasquez (talk) 20:30, 29 December 2007 (UTC)

Life as we know it?

The article talks about life as we know it as if it needed water. This isn't true, we've found lifeforms that live on radiation, so what is the definition of "life as we know it"? E9 06:41, 28 April 2007 (UTC)

Those bacteria still rely on water [9]. As far as I know all life on earth depends critically on water. Many organisms can survive dessication, but will only begin replication again in the presence of water. It is, speculatively, still possible that organisms on other planets have substituted another solvent for water in their make up. Debivort 06:49, 28 April 2007 (UTC)

...Um... E9, Debivort is right. What lifeforms (outside of science fiction) might those be? Esseh 06:52, 28 April 2007 (UTC)

This is just human inability to imagine life that's any different from ourselves. I know people who refuse to believe in bacteria... Viruses don't need water, do they count as life?
Esseh, if you give me a description of what the inside of the sun might look like, I'll be happy to give you a description of what lifeforms they might be.
Oh, and those bacteria only need water for energy, which they release using the radiation. E9 07:07, 28 April 2007 (UTC)

...Um... so we're down to "imagine", are we? Like I said, give me one example of a known life-form that doesn't need water. Not what "they might be", not what you (or anyone else) "imagine" them to be, cut a concrete example, preferably with a reference. As for virsues, no, I personally don't consider them "life", but that is a matter of interpretation. They DO need water to reproduce, since they must infect living (watery) cells to reproduce. Esseh 07:15, 28 April 2007 (UTC)

You asked what they might be, not what they are.E9 07:19, 28 April 2007 (UTC)

Oh, alright, I give up. E9

Sorry, I didn't know the language was a problem. My mistake. So, what is one example? Esseh 07:26, 28 April 2007 (UTC)

Sorry - saw your second post just after I'd posted. No worries - it's about learning, too. No, all life as we know it requires water. Absolutely essential. This does NOT mean that all life everywhere will, but just that its all we know right now. This is largely due to the physical properties of water. It would be really cool to discover something that doesn't need it, but I can't even imagine what! Esseh 07:29, 28 April 2007 (UTC)

(Oh, I would have left you a message on your talk page, but it's unreadable! Sorry. Esseh 07:33, 28 April 2007 (UTC))

Is the possibility of a moon excluded?

It may be a stretch to call a planet with 1.6G gravity "earth-like" or potentially habitable by humans. Is there, however, any way to exclude the possibility that Gliese 581 c is a double planet system like the earth-moon system, in which case one or both planets could have gravity in the more tolerable range. Bob99 13:23, 27 April 2007 (UTC)

It's a nice possibility. However I'd stick with the (few) facts we have at hand; and those facts are just that there is a larger-than-5 Earth-masses thing orbiting Gliese 581 at that distance. Let's let speculation to scientists working on it. --Cyclopia 13:34, 27 April 2007 (UTC)

I think by habitable, Udry et al. mean habitable by any organsim, and they are probably thinking microbes. All they really mean is the calculated meant temperature range allows liquid water. And, it is NOT a gas giant (ie saturn mas or larger). Is that clarified on the planetary habitability page? IMHO 1.6g surface gravity would not be a huge problme for humans, but that is not the point Rich.lewis 16:39, 27 April 2007 (UTC)

Moons are unlikely for a tidally locked planet, since the orbit of any moon of a tidally locked planet will eventually decay until the moon reaches the Roche limit and is broken up. Since Gliese 581 is estimated to be 4.3 billion years old, that would have already happened, I believe. This theory also explains why Mercury and Venus have no moons, and also whey there are no known secondary moons in the Solar System. Vegasprof 17:28, 27 April 2007 (UTC)

"Free-fall acceleration"

This material was included by User:Temurjin, with the claim that "the free-fall acceleration on Gliese 581 c is different by 0.7 m/s^2 between the day and night side, as compared to 0.01 m/s^2 on Earth" (I paraphase). It is not clear to me what this means, or why it is at all relevant to the article. I can think of several possible meanings, which I will go through here. Michaelbusch 02:46, 28 April 2007 (UTC)

• The acceleration on Gliese 581 c from its primary. The primary has a mass of 0.31 M_sun and is at a distance of 0.073 AU, so its acceleration on the planet is .35 m/s². This is the only value I can think of that might give Temurjin's value, if it were doubled for some reason, but that number is meaningless: it is simply the inward acceleration that the object feels towards the star, and is implied in the orbit. It has nothing to do with the day or night sides of the planet.
• The tidal force across the object. This evaluates to 3e-4 m/s², which is larger than the Earth, but that is simply saying that the tides are stronger because you are closer to the star.
• The centrifugal force from the object's rotation. That is also ~3e-4 m/s², assuming it is tidally locked and has the smallest reasonable radius.

None of these are what Temurjin described, and none are notable enough to be given special mention. Michaelbusch 02:55, 28 April 2007 (UTC)

I agree with you now. I was wrong. Temur 03:08, 28 April 2007 (UTC)

Centrifugal orbit effects on the gravity. From the planet being whipped around the primary like a centrifuge. The force is always there, (regardless of rotation, tides), and adds to the gravity when the primary is down, subracts from the gravity when the primary is overhead, giving a total difference of 0.7 m/s², significantly more than Earth. If the planet were small enough you'd even have no gravity at all on the anti-stellar point. Sagittarian Milky Way 16:24, 28 April 2007 (UTC)

It doesn't work that way, because you are in free-fall: that acceleration doesn't matter except to keep you in orbit. And given that the object is tidally locked, what you propose wouldn't work anyway. Michaelbusch 16:26, 28 April 2007 (UTC)

Sagittarian, I also though that way first. But the problem is that the star's gravity affects not only the planet also any object on the planet too. That means even the planet wasn't there those objects still be orbiting around the star. Temur 20:17, 28 April 2007 (UTC)

Doi, it's in orbit. My mistake. I was thinking of a higher analogue to what happens with rotation. Sagittarian Milky Way 23:16, 28 April 2007 (UTC)

Tide locked claim

It should be mentioned that the claim that the planet is tide locked is wild speculation. In our case it is actually not that likely that a tide lock has been established, considering the radius of the planet and the mass difference between it and Gliese 581. Themanwithoutapast 07:39, 25 April 2007 (UTC)

Maybe, maybe not. What's not debatable is that scientist has made that claim. If some other article makes the claim that it can't be tidally locked then we should quote that in our Wiki article as well.

I have read numerous papers on the subject of planets of red dwarfs, and plan to put up some interesting stuff. There's no direct proof that Gliese 581 c is tidally locked, but, according to current theory, it is essentially impossible for it not to be, given the age of the star and the tidal drag. Interestingly, the Gliese 581 b is close enough to raise noticeable tides on the oceans of Gliese 581 c, if it has oceans. Vegasprof 11:20, 25 April 2007 (UTC)

Given that Gliese 581 b is roughly Neptune-mass and orbits within the orbit of 581 c, I find it hard to believe that it'd be "essentially impossible" for 581 c to not be tidally locked, if "locked" is assumed to mean a 1:1 resonance. Some other resonance lock perhaps, given 581 c a slow rotation relative to the primary. The orbital periods for 581 c and 581 b look close to a 2:5 orbital resonance, although rotational resonance may be different. Orbital eccentricity also plays a role (as with Mercury's resonant rotation). "Impossible" is a strong word for a four (at least) body system whose parameters are deduced from the wiggle of the primary. AJWM 04:51, 28 April 2007 (UTC)

At any rate, the claim that that the planet would be completely inhospitable for life is NOT made in the SF Chronicle's article, so I removed that bit from our article here on Wiki. In fact, the SF Chronicle quotes the scientist as saying "life might well exist in that difficult environment." Egumtow 08:06, 25 April 2007 (UTC)

Ok, fair enough. One point that should be mentioned as well is the high surface gravitational forces compared to Earth. Assuming the mass and radius of that planet are estimated correctly the g-loads are nearer to those on the surface of Jupiter... Themanwithoutapast 08:57, 25 April 2007 (UTC)

http://apnews1.iwon.com//article/20070425/D8ON9PUO0.html mentions its gravity is "1.6 times as strong as Earth's so a 150-pound person would feel like 240 pounds." I'll add this in. Egumtow 09:06, 25 April 2007 (UTC)

Some news articles are written by the scientifically illerate. There is no need to quote these when there are good articles out there. I fixed the mass and the surface gravity, using data from a more reliable source, the Extrasolar planets encyclopedia. Please note that the widely quoted radisu of 1.5 Earth is a guess, as opposed to mass, which is estimated based on observational data, and hence should be fairly accurate. Vegasprof 11:18, 25 April 2007 (UTC)

Agreed. It's a very discouraging fact that we can't trust a scientific Associated Press article. Egumtow 18:07, 25 April 2007 (UTC)

It has been my experience that the general press (e.g. AP, BBC, NYT, etc) commonly makes notable technical errors in their coverage of technical topics like this. Not a universal flaw in EVERY story's coverage, but it's far from uncommon. :-( - Steve

I know a 150 pound person whose weight grew to 240 pounds over the years, and who manages just fine! Edison 17:43, 25 April 2007 (UTC)

Many astronomers have done surveys on this subject, and their opinions are widely varied. The chronicle article should be taken with a grain of salt, as it is written for a public audience and the possibility of life sells much better and is more interesting to readers than any theories that suggest otherwise. Most reliable planetologists would agree that is highly likely that, even if a region existed with habitable temperatures (defined as being within the liquid range of water) volatiles would tend to condense on the permanently dark and frozen side of the planet. It is also a possibility that the planet, much like mercury, might posses a stable orbital resonance other than 1:1.-Willy

It is called "atmospheric collapse" when the whole atmosphere freezes out on the dark side of a tidally locked planet, or on a planet like Pluto as it gets farther from the Sun. Recent models have indicated that this will not happen to a tidally locked planet if the atmosphere is think enough; something like only 20% of the Earth's is enough to stop it. although I'm sure it's complicated. There are a bunch of articles appearing in 2007 relating to habitability of red dwarf planets, all of which, if within the habitable zone, are presumed to become tidally locked within the first billion years or so. I plan to put some of that stuff on Wikipedia when I get a round TUIT. Basic summary: these planets are not as inhospitable as previously believed. Vegasprof 21:05, 25 April 2007 (UTC)

Twilight Zone reference

There is no proof that this plant is tidally locked and has a twilight zone (any more than Earth does).
This is another deception to push the idea that "we can go there."
If there is any orbit sync to this planet other than 1:1 then it does rotate its face. A 1:1 ratio is the only arrangement in which it would not rotate its face (ie. twilight Zone), and that has not been proven.

Detecting the atmosphere

I think this comment in the article is not correct, "Techniques such as the one used to measure

You're correct, Gl 581 c is not a transiting planet and even if it were I don't know if it is possible to use that method because the star is so dim and the planet is so small.— JyriL ^talk 14:41, 25 April 2007 (UTC)

Someone should update the article to reflect that this planet is not a candidate for the atmoshphere technique mentioned. Conversely, are there any techniques that might be applied? We should mention those. Egumtow 18:09, 25 April 2007 (UTC)

What about the radius? If the planet isn't transiting planet we cannot definitely measure it's mass nor radius, just minimal possible mass. All the rest is assuming Amakthea computer 20:29, 25 April 2007 (UTC)

I think that

BlueEarth

22:00, 25 April 2007 (UTC)

Greenhouse Gas Effect

Atmosphere

Hi there.

If Gliese 581 c can host life depends, of course, on whether it has an atmosphere. But can it have an atmosphere? Wouldn't "solar" wind (Gliese 581-ar wind?) from its star blow off the atmosphere of an object so close to it? Given the short period of 13 days, the planet must be very close to its star; Isn't Mercury (having an 88-day period and thus much further removed from the Sun than Gliese 581 c is from its star) thought to have lost its atmosphere because of the solar wind. Or is the solar wind from a red dwarf so weak that it can't possibly blow off atmospheres? Steinbach (fka Caesarion) 15:14, 12 May 2007 (UTC)

There's been much hype in the media about the possibility of life on Gliese 581 c, but the article tries not to give it undue weight. Here on the talk page we can say things like Gl581c is probably either Venus-like or a small gas giant. Reasons it could be uninhabitable are easy to enumerate. It's likely something better will be discovered soon. Glycerinester 09:35, 15 May 2007 (UTC)

I agree. We really don't know whether Gliese 581 c is habitable. To answer Steinbach's question, the solar wind from a red dwarf is a serious issue, just like for the Sun, according to the latest papers I've read. Mercury has a magnetic field which, as I recall, is strong enough to protect it from the solar wind, despite the fact that it rotates very slowly. So, it seems perfectly possible for a red dwarf planet to have a strong magnetic field. My concern for Gliese 581 c's atmosphere is the opposite: its escape velocity (approximately 20.5 km/s) is almost as much as Uranus, assuming a radius of 1.5 Earth and a mass of 5 Earth. If it could hold hydrogen (which Uranus does), it might have a very thick atmosphere, and the solid (liquid?) surface could be so deep that life would be impossible. Vegasprof 11:02, 15 May 2007 (UTC)

I wouldn't say impossible. the planet could still have seaweed and fish. --Marhawkman 01:21, 16 May 2007 (UTC)

You can't just compare Uranus to a Supervenus, there's two factors for atmospheric retention -- escape velocity and temperature. Nevertheless, I looked at [10] (unfortunately the density slider doesn't go far enough) and it looks as though the planet is on the cusp, hard to tell. Sagittarian Milky Way 03:37, 16 May 2007 (UTC)

Note: You might need to use Opera to see the link. Sagittarian Milky Way 03:41, 16 May 2007 (UTC)

I apologize if my question sounds stupid, but I'm not an astronomer, physicist, or evolutionary biologist. The

Aurelia that possibly resembles Gl581c, i.e. a tidally-locked terrestrial planet orbiting a red dwarf star. In the NGC special, complex (multi-cellular) life is supposed to have evolved in an environment like Aurelia's, despite the tidal lock and associated extreme conditions. Is that really possible ? Or is it completely absurd ? 161.24.19.82

20:14, 16 May 2007 (UTC)

But that assumes it is a rocky planet. If it's watery planet the equation becomes much different. On a watery world it might be possible for there to be life over around 50% of the planet instead of just he narrow terminator. Why? The water covering the surface would display the same sort of convection as the air above it. This would redistribute the heat more evenly.--Marhawkman 23:57, 16 May 2007 (UTC)

What a crystal ball is

OK, I've put in my own version now, meant as something of a compromise. As a 'Further study' section, it can now largely focus on future telescopic observations, which in the short and medium term would of course be all there is to talk about. I feel that only one direct quote is necessary, the general one from the person on the discovery team. Discussion of the possibility of a probe has now been simplified and condensed into one exaplanatory statement.--Pharos 23:11, 28 April 2007 (UTC)

Suppose one gathered together a number of imminent scientists, in the presence of a reporter from the New York Times, and they went on record as to saying a number things like "You know, if we have computers 10,000,000 times faster and a corresponding information storage capacity, Star Trek teleportation is a near certainty!" The question is: is this knowledge? Or just a bunch of guys rag-chewing? Does the fact the well-masticated cloth was printed in the NYT make it any different from random blow-hards arguing in a bar about

WP:IAR. My recommendation would be that conditioned knowledge -- if P then Q -- may only enter the encyclopedia when the antecedent (P) is currently known to be true^{[citation needed]}, and the subsequent (Q) is either true^{[citation needed]} or almost certainly true (or false, depending), as discussed by the sources. That is, material talking about what a famous physicist thinks about teleportation and computers may only be added to those articles as soon as that computer exists (or well on the way). mdf

18:16, 30 April 2007 (UTC)

Ignoring what eminent scientists say just because you consider it to be unreasonable would be original research. Look, if we actually followed your proposal, we would have to delete all articles like interstellar travel outright, or even worse, just restrict them to discussions of science fiction. Do you really think that would increase the educational content of the encyclopedia, when people could learn about science fiction, without having any idea whether such ideas have any scientific validity? Of course each one of us I'm sure can point to individual cases where we think reliable sources are wrong, but overall they generally have more validity than our personal opinions, which is why we have that policy. Anyway, as has been pointed out, NASA and others have conducted several serious studies for an interstellar probe, which is reasonably thought by many experts as a possibility for launch in the coming decades, so I'm not sure why you think this is such a stretch in the first place.--Pharos 19:26, 30 April 2007 (UTC)

I have no idea how excluding speculation can achieve a new, unpublished result. Can you explain? And you'll also have to explain why this proposal would require the removal of interstellar travel. That article appears to be a summary of extant literature on the subject, not the regurgitation of the idle speculations of a Famous Person in the New York Times. And I'm glad you mention "educational value", as it plays directly to my point. Of what value is it diluting the real, educational, content of this article (or any other) with outrageous speculations of anybody? That they are reported in the NYT doesn't make them any more educational. Recall that the purpose of this project is not to closely follow what every last media outlet has said, but to convey knowledge as of now. Please re-read my proposal in that light. Now, as to why I think think any claims of "going there" are wild, over-the-top nonsense, you can read them (above). Once infrastructure begins to take shape, we can begin to entertain some of this stuff seriously. mdf 20:27, 1 May 2007 (UTC)

Ambigous stats

The article says it is 20.4 light years away, and BBC News says it is 20.5 light years away. Which one is the correct one? OhanaUnited 01:58, 26 April 2007 (UTC)

Yahoo news also reports it as 20.5. [11] Darry2385 02:21, 26 April 2007 (UTC)

...a trip length of approximately 782,287 years should a shuttle travel to the body's location at the achieved speed of 17,500 miles per hour. Does this really need a citation? It is simple Math. Harakim 02:41, 26 April 2007 (UTC)

No, it doesn't. It's irrelevant. But it appears somebody already took it out. Darry2385 03:09, 26 April 2007 (UTC)

... speaking of which, I changed the linguistic and mathematical idiocy "14 times closer". Its orbit is 1/14th the distance compared to the terran orbit. Journalists like meaningless "stats" like this, but we're supposed to be an encyclopedia here. Esseh 03:43, 26 April 2007 (UTC)

Then I guess it's safe to change it to 20.5 light years unless someone finds a source that says 20.4 light years. OhanaUnited 05:29, 26 April 2007 (UTC)

The Gliese catalog suggests 20.65±0.85 light years. Gliese 581 is HIP 74995, and the entry in that table says the parallax is 159.52±2.27mas, which maps to 20.449±0.29 light years (see http://www.rssd.esa.int/Hipparcos/HIPcatalogueSearch.html). mdf 12:35, 26 April 2007 (UTC)

The shuttle's earth orbit velocity is irrelevant. A better stat would be Voyager 1's velocity of 38,400 miles per hour, as it leaves the solar system. Edison 14:17, 26 April 2007 (UTC)

But the probes are decelerating. Anyway, New Horizons is supposed to pass the Voyagers in the 2200s. Sagittarian Milky Way 22:58, 27 April 2007 (UTC)

Embargo

Is this embargo for real? Here is a new link from space.com: http://www.space.com/scienceastronomy/070424_hab_exoplanet.html Hiberniantears 21:12, 24 April 2007 (UTC)

It's all over the net. I think since the embargo seems to be widely ignored [12] it becomes void, especially since they didn't inform us in the first place. Unless we have a better reason than "it's not nice", this should stay up. -- Stereo ^(talk) 21:24, 24 April 2007 (UTC)

Agreed. There is plenty of information on this planet in the public domain already to expand this article considerably.Hiberniantears 21:26, 24 April 2007 (UTC)

Ç:::Besides, could ET mean European Time? Why would Swiss astronomers use Eastern time? I think the embargo shouldn't, and doesn't seem to, apply anymore. -- Stereo ^(talk) 21:37, 24 April 2007 (UTC) Embargo? --NEMT 00:14, 25 April 2007 (UTC)

There is no time zone called "European time", but Switzerland uses Central European Time which is standard for most European nations. Valentinian ^{T / C} 11:00, 25 April 2007 (UTC)

News embargo. It was widely flouted, but now it's moot, as the time has come and gone. Gliese 581 turned into the hottest star in the Galaxy, and the eruptions could not be contained.  :-) Vegasprof 02:17, 25 April 2007 (UTC)

Intelligence

"On Wednesday, April 25, 2007 at approximately 01:45 GMT unofficial confirmations were received that intelligent radio transitions were being detected originating from the direction of the Gliese 581 solar system."

This sentence states that "intelligent radio transitions" were being detected. Does the author mean "transmissions"? --Spiralout987 01:01, 25 April 2007 (UTC)

It's obvious vandalism...but one can hope. :(68.160.218.93 01:02, 25 April 2007 (UTC)

damnit, I was hoping for something more.  :( --Spiralout987 01:03, 25 April 2007 (UTC)

Yeah, it's not even 01:45 GMT yet --68.248.89.178 01:08, 25 April 2007 (UTC)

Vandalism. If I recall correctly, the space.com article explicitly said the system had been scanned for signals twice in the past and nothing was found. - green_meklar 17:26, 25 April 2007 (UTC)

The planet's only 20 light years away - next door in Galactic terms! Oh dear, if there's anyone there, they might think that Reagan & Thatcher are still in charge... I think it's worth keeping a close eye on this page to protect it. Darkmind1970 13:57, 25 April 2007 (UTC)

When I read that, I just stared at my computer screen for about 20 minutes, (didnt notice the "transitions" word) without blinking or anything. Then, I clicked on discussion, went back to it and it was gone. Damned vandals. :( --DS7202

When will they announce the range of IP addresses allocated to Gliese 581, so we will be able to recognize any anonymous editors from there who might have conflict of interest in their edits to this article? More seriously, [13] describes the development of the Interplanetary Internet and the Consultative Committee on Space Data Systems (CCSDS), which is an international organization chartered to establish space telecommunications standards,and how a specialized internet to allow long delays and error filled data is being developed for communications with probes on Mars. Edison 17:40, 25 April 2007 (UTC)

Really? THAT Steven Fry?

I think that the Steven Fry in the article links to the wrong

Yeah, looks to be a different person, his first name is spelled differently (Stephen Fry). Steven Fry is a redirect there currently, maybe someone who knows a bit about him can turn the redirect into a stub. using the {{ otheruses4|topic|other topic|location }} template on both of those pages would probably be a good idea. That gives:

--Eloil 12:08, 27 April 2007 (UTC)

• At the moment, the link appears to have been removed, so the redirect stays.

(varying) External link

An EL to Nasa Astonomy Picture of the Day ([14]) that shows a concept sunrise of Gliese 581 c, was recently added. But since it will change everyday, I think it should not be linked. Rather, if needed, the image can be included here. --soum (0_o) 11:13, 2 May 2007 (UTC)

It is a hard link to the actual APOD page, that page won't change every day (see the 070502 date in the URL?). However, I doubt the informative value of that (indeed nice) image, so I wouldn't include it (copyright problems notwithstanding). Also the concept of "sunrise" on a tidally locked planet is quite odd: you would see the sun "rise" by moving towards the center of the Sun-lit emisphere, and "set" by moving away from it. On a fixed point on the terminator (where the picture is actually showing) the sun would just appear frozen on the horizon. --Cyclopia 09:12, 3 May 2007 (UTC)

removed img

I removed the copyrighted "artist's impression" as indefensible under "fair use". Fair use could be argued if we had some actual HARPS footage with would fall under "not reproducible", but a fanciful drawing of a planet orbiting a red dwarf may be reproduced by any Wikipedian who has the patience to sit down for an hour or two.

Any wikipedian? I, for one, couldn't draw my way out of a wet paper bag.

dab has created a nice free image discussed here.--Pharos 06:36, 27 April 2007 (UTC)

image

Consider also using: Image:Gliese 229 B.jpg Bawolff 01:36, 25 April 2007 (UTC)

nevermind that's cm not b.

How about a better context image ? Where in the sky should people be looking for the star associated with the planet ? Celestia can be modified, with a script (Celestia forum post about star labels) to show many more star labels that would put this planet into a contextual location in the sky.

DJ Barney

17:40, 26 April 2007 (UTC)

Hydrosphere image

Could I include this image in the article? It's an diagram of what the hydrosphere of a tidally locked planet with water oceans would likely appear. — Jack · talk · 00:32, Saturday, 28 April 2007

It's not clear from the arrows how the water is returned from the cold side to the warm side, also wouldn't the water evaporate on the warm side, also is this

WP:OR? Debivort

00:37, 28 April 2007 (UTC)

The water would evaporate on the warm side. Winds would carry it to the cool side, where it would condense into rain and (potentially) freeze on the cold side. However, I don't know either how the water would return from the cold side to the warm side. The Dark 00:47, 28 April 2007 (UTC)

Well I see it as Gliese 581 c being so huge that it assumes a hydrostatic equilibrium. Huge mountains of ice would flow to lower grounds. Not very fast though, hence the smaller arrows — Jack · talk · 00:57, Saturday, 28 April 2007

Plus, there's always the tidal force — Jack · talk · 02:01, Saturday, 28 April 2007

We don't know that this thing has a hydrosphere. My bet is on deep global ocean (large fraction of planetary mass), in which case your approximation doesn't work, but that is just a shot in the dark. Michaelbusch 02:56, 28 April 2007 (UTC)

Jack, please! Michaelbusch is right. You had a problem with the habitable zone graphic, but you want to include what the hydrosphere looks like? We don't even know if there's water there, miuch less oceans. It is a very well-done graphic, though. Esseh 07:22, 28 April 2007 (UTC)

Lol, super-mega agree with Esseh. I just wanted to provoke discussion (shock-horror at bending the rules of

WP:TALK!) Oh, and, cheers for the kudos; it's amazing what you can do with Microsoft Paint. — Jack · talk

· 01:50, Sunday, 29 April 2007

Agreed that this whole discussion is irrelevant, but also if Gl581c is tidally locked, then the hydrostatic equilibria for the planet and the hydrosphere would be approximately the same shape. The rocky body would not be more spherical than the ocean. 24.20.137.228 14:36, 28 April 2007 (UTC)

Not so fast: the composition of the object determines its equation-of-state, which determines the degree of mass condensation, which determines its reaction to stress. But we are now well into theory and I will stop. Michaelbusch 16:05, 28 April 2007 (UTC)

Here's a weird thought.... A Tidally locked body has it's orientation determined by the center of mass. If something like migration of water causes the center of mass to change, would that also change the body's orientation? —The preceding

unsigned comment was added by Marhawkman (talk • contribs

) 20:27, 28 April 2007 (UTC).

That's exactly what I thought! You stick something (no matter what) in a gravity field, and make it top heavy, it'll try and spin to make the most massive side face "down". Surely the mass migration of anything from one side of a planet to another will produce torque? — Jack · talk · 01:50, Sunday, 29 April 2007

Yeah. I thought of this afte remembering that Earth's moon is beleived to be tidally locked, at least in part, because of it's center of gravity being different(and in the side closer to Earth) from it's actual center.--Marhawkman 15:11, 30 April 2007 (UTC)

New pic & non-journalistic references

Hi all. A couple of suggestions for articles like this. If we must use media as the only references (at least in the short term), can we lose the meaningless journalistic terminology? "14 times closer" is meaningless (think "twice as small"). Similarly, "gray line", and water and carbon dioxide as "elements". These I have changed, but I'm sure there are others. Finally, couldn't someone modify the stock image used at the end to show where in the potentially-habitable zone this planet would lie? (i.e. add a ball 1.5 times the shown Earth size to the lower left of the zone.) That would be much more meaningful than the standard stock pic shown now. Just a couple of thoughts. Esseh 04:08, 26 April 2007 (UTC)

I just changed the last pic in the article. Check it out, let me know what you think. Esseh 16:08, 26 April 2007 (UTC)

I've made another new version of the image at Image:Gliese 581 c in the habitable zone.svg. The graph had to be extended downward to accurately represent the mass of Gliese 581. I'm no visual artist, though, so it might need some tidying up by someone with more than 10 minutes' experience in svg editing. - Ben Ram 23:06, 26 April 2007 (UTC)

Thanks Ben Ram. Looks pretty good to me. I just extended the end downward, and found the planet (at 0.07 AU from the star) didn't quite fit into the habitable zone. As you say, the zone is hypothetical (and sketchy) at best. Good work. Esseh 00:24, 27 April 2007 (UTC)

12.4 New Image

I revised Image:Gliese 581 c Celestia.png to include a greater highlighting on several of the objects in the field, and larger labels Latitude0116 02:26, 28 April 2007 (UTC)

Photo

The photo of system of Gliese 581c is wrong, it is in Libra's constellation and not constellation of Taurus. Sorry for my English from Pifoyde wikipedia Italia. 83.189.215.48 20:47, 29 April 2007 (UTC)

That's because the rendition, (not photo) is looking back on the solar system, so the star is in the opposite direction. Sagittarian Milky Way 23:59, 29 April 2007 (UTC)

Good point. Temur 03:17, 30 April 2007 (UTC)

new graphics

As an alternative to Image:Gliese 581 c in the habitable zone.svg (right) I've hacked up two alternatives, depending on what concept of a habitable zone you subscribe to:

File:Habitable zone with Gl581c and Gl581d.svg

and

File:Habitable zone (bigger).svg

Glycerinester 00:26, 1 May 2007 (UTC)

The diagram portrays Gliese 581 c a bit on the warm side of Venus with respect to the habitable zone. Is that interpretation in accord with the diagram? Edison 05:35, 3 May 2007 (UTC)

In accord with the diagram, and with the numbers:

 planet         L       a
 
 MERCURY        1.0     0.387 099
 VENUS          1.0     0.723 332
 EARTH          1.0     1.0
 MARS           1.0     1.523 662
 CERES          1.0     2.766
 JUPITER        1.0     5.203 363
 
 GLIESE 581 b   0.013   0.041
 GLIESE 581 c   0.013   0.073
 GLIESE 581 d   0.013   0.25

The heat radiation power per square meter that a planet gets from a star is called irradiance.

the irradiance E at each planet (vs. the solar constant)

equals the bolometric luminosity L of its star (vs. the solar luminosity)

divided by the radius a of its orbit (in AU) squared

 planet    L        a               E
 
 gl581b    0.013 /( 0.041     ^2) = 7.733
 mercury   1.0   /( 0.387 099 ^2) = 6.673 537
 gl581c    0.013 /( 0.073     ^2) = 2.439       hotter than venus
 venus     1.0   /( 0.723 332 ^2) = 1.911 281
 earth     1.0   /( 1.0       ^2) = 1.0
 mars      1.0   /( 1.523 662 ^2) = 0.430 747
 gl581d    0.013 /( 0.25      ^2) = 0.208
 ceres     1.0   /( 2.766     ^2) = 0.131
 jupiter   1.0   /( 5.203 363 ^2) = 0.036 934

Media reports that say things like "In our solar system, only one planet -- Earth -- lies in the Goldilocks Zone. Venus is far too hot and Mars is just too cold. This new planet lies bang in the middle of the zone" are grossly misleading. Glycerinester 11:20, 3 May 2007 (UTC)

Yes, I suggest we replace the diagram with your second version (the broader habitable zone). Not sure if we need Gliese 581 d, though. Also, we might want to update commons:Image:Habitable zone-en.svg--Pharos 14:51, 3 May 2007 (UTC)

Or maybe, should we have a two-tone habitable zone (distinguishing the fringes from the central band)? Or would that not be scientifically justifiable?--Pharos 14:58, 3 May 2007 (UTC)

Or a fuzzy zone? Sagittarian Milky Way 19:40, 3 May 2007 (UTC)

Too many variables... Add a nice "greenhouse" atmosphere to Mars; it's habitable. Without, it's not. Add a reflective albedo to Venus; it's habitable. Without, it's not. None of these have anything to do with distance to the star (Sol) itself, but to planetary characteristics combined with distance from the star. OK, now add internal thermal characteristics (warmth from the planet core itself), with a really great atmosphere and Pluto is habitable. Not very likely, agreed... but possible. So where, exactly, is this "habitable zone", and how big is the "fuzzy" layer? Just too many assumptions. I remember a prof of mine saying that when you ASSUME you make an ASS out of U and ME. Esseh 22:08, 3 May 2007 (UTC)

Artistic Impression Review? (!)

Based on these discussions, I firmly believe one should be started in a manner similar to the Wikipedia:WikiProject Dinosaurs/Image review. Editors could go to it, post a request for an image, with scientific guidelines, such as distance from star, star type, planet type. Then artists could claim the task, generate a draft image, post it, receive critiques, and modify as appropriate. Please look at the Dino review page to see plenty of examples of it. They system works well there, and there is an active community of artists that keep it lively and productive.

So is there a consensus to start this? If so, I will happily set it up. Debivort 22:11, 9 May 2007 (UTC)

• support idea Debivort 22:11, 9 May 2007 (UTC)

If this is what I think it is then I support it.

• support idea Fusion7 23:50, 9 May 2007 (UTC)

• support idea I was actually already thinking of something similar to this, the only difference I would suggest is the strategy. Rather than request images for a specific planetary system I think it would be much better to develop a catalog of planet skins based on something like 4 parameters; for example type (rocky, icy, gas), mass, atmospheric density, and solar flux per square meter (at the top of the atmosphere). Once you have a decent catalog built up its trivial to render them in something like Celestia to see how the orbits relate, or what the star looks like, etc for any new system of planets. This seems rather wasteful at this point but we have to keep in mind the fact that we will likely be discovering many thousands (~200 right now, most in the last few years) of planets in the near future, almost none of which will be able to image directly. Secondly this would help avoid potential biases because the images would be based strictly on measurable data, and not by the particular media hype around a particular planetary system, such as this one. Finally it would be easy to set a policy for image use in these articles based on something like until at least 3 of the four criteria are known we must either have no picture or show a range of pictures showing possible renditions for various values of the unknown parameter. As for the Gliese system according to the policy just stated and my current opinion it is too early for pictures. Type unkown (rocky or icy?), mass unknown (only lower bound), atmospheric density completely unknown, solar flux, the only currently known parameter. By providing images for every known planetary system based on the best scientific "picture/data" we have for that system and avoiding raw speculation and bias like we and most of the other media currently do, we could really put Wikipedia in a league of its own, at least in this aspect. --AndrewBuck 00:11, 10 May 2007 (UTC)

I'm not opposed to any of this, but I suspect Debivort knew what he or she meant when he or she made the proposal. Artists like to make works of art, not just Celestia skins. There's not much difference between banning artistic impressions and restricting them to Celestia geeks. Glycerinester 04:20, 10 May 2007 (UTC)

Yeah, this discussion is deflating my enthusiasm, since I find the celestia images rather unappealing aesthetically, but if that is how people think the planets should best be illustrated - go for it... Debivort 04:39, 10 May 2007 (UTC)

I didn't mean to imply that only Celestia images would be allowed or even that we should primarily use them. Celestia and programs like it are good for showing the orbits of a planetary system, etc. If you want to hand draw pictures like what are in the article now thats great, they are far better than anything I can draw, and as you say are much more visually pleasing than computer generated scenes. I am merely suggesting a change from asking for an image to be hand drawn for a particular planet, to building a more general library of what various planetary configurations would look like. Each place in the library need not even be restricted to a single image. I just think its much less prone to unscientific bias which is something I think this class of articles is especially prone to, especially ones like this that get lots of media coverage. Also when situations pop up like this where the article is created long before much about the planet is known it makes it easy to pick out three or 4 not just different pictures but truly different planets, i.e. dense atmosphere vs none at all, instead of 5 or 6 slightly different variations of what we hope is there. --AndrewBuck 05:32, 10 May 2007 (UTC) Amended Message: My primary goal is simply a catalog or index of the images people can/will produce by the physical properties of what is portrayed in the picture. If you create a picture by any means of a small rocky planet with adense atmosphere then it should be clearly tagged with a template, put in a category, named a certain way, whatever. Just so that pictures used in the articles agree with what the article says. When signfigant properties of the planetary system are unknown we should have an easy way of showing the variuos possibilitys. A catalog makes that very easy regardless of how we actually implement it. Also I am not entirely opposed to the idea of people requesting images for a given article, but if an when the image request is fulfilled the image needs to be evaluated to determine what type of planet it represents and properly tagged like any other picture of a planet. As before this makes it easy to find pictures that go with planets because we will likely be finding many thousands of them of all reasonable configurations. Properly tagging the images makes it easy for people to add pictures to these articles and have them still be a good representation of our current understanding of the planetary system. I supported the proposed idea as it stood at the top and was just looking ahead at how these and future images could be organized as it looks like there are quite a few already. Thus far it looks like there is almost unanimous support for the original idea with the only difference in opinion being how to actually proceed after that which is something I think would be better worked out there. --AndrewBuck 06:06, 10 May 2007 (UTC)

The control for unscientific bias would be that each image has to attain a community consensus before it is placed in articles, as in the dinosaur image review pages. Debivort 05:51, 10 May 2007 (UTC)

I would sound stupid if I said what do dinosaurs have to do with GLIESE 581 C, but I have to clarify that there seems to be several tangents above. You are putting Artistic Drawing and techinical diagrams in the same boat. It struck me that there is so much emphasis on the idea of Habitiability in this article and then a technical artist like Glycerinester gets his very accurate diagram shot down because it conflicts with that bias. What are the guidlines for this evaluation of what images meet the standard of known values for the planet in question? Who is to say that my Rocky planet image is Rocky enough for someone else. Who is to say at what point it is certain enough when the planet in question is Rocky and not icy? Incidentally the idea/suggestion that this is an Icy planet is absurd given the Isolation/Heat.On the tangent of Celestia, I agree Celestia geeks don't have the planet image area cornered by far. It takes a fair amount of knowledge and experience with Celestia to get a printscreen snapshot that's worth looking at. I don't consider the usual Celestia image artistic or technical. - GabrielVelasquez (talk) 20:00, 30 December 2007 (UTC)

• support idea Totally agree. If done as per AndrewBuck will bring a new level to Wikipedia planet renditions. Sagittarian Milky Way 00:31, 10 May 2007 (UTC)

• support per AndrewBuck. Seems quite reasonable. Esseh 00:44, 10 May 2007 (UTC)

• Kind of support. I like Andrew's ideas, although it's worth noting that Celestia already includes an up-to-date catalogue of extrasolar planets with about 5 or 6 basic 'standard' textures (there's a standard 'rocky planet', 'gas giant', 'hot jupiter', etc.), so there may not be any need to devise new 'skins'. I'm not sure if these textures are in the standard Celestia release (1.4), but they are in the recent prereleases e.g. pre5.2 available here. If these are usable, it would make it very easy to produce acceptable images without too much artistic licence, and Celestia is free under GNU.
  Cop 633
  01:51, 10 May 2007 (UTC)

• The catalog would be mutually benefcial to Wikipedia and Celestia, and I think sharing between them would be a good way to start. From what I have heard about it Clestia is geared towards scientific accuracy and I think that is the best way of rendering the final scenes (Orbiter does a fairly nice job as well). However, even 20 different models would be a very small fraction of a complete 4 dimensional catalog (low, medium, high values for each parameter yield 3^4 = 81 possible planets). Going any bigger than this makes the number of necessary models go up quite fast however I think 4 or 5 variations per parameter would be good (4^4 = 256 ; 5^4 = 625). Although the number needed to completely fill a catalog like this grows very rapidly there are two things that make a complete catalog unnecessary. First, some planetary configurations may be impossible or exceedingly rare. An example would be a low mass planet with high solar flux and a dense atmosphere. This entire region of planets could be left out of the catalog will little or no ill effect on the articles. Second, it may not be necessary to hand draw all of the dimensions as Celestia may already handle it. An example would be the atmospheric density. I'm all for working Celestia's imagery and possibly even planets from our solar system as points in the catalog but I think continous variation of a few parameters would be a great way to organize it. Simply organizing them in this type of 3 or 4 dimensional space makes it easy to find pictures for articles, and shines a light on potential biases (example: all of the pictures in this article fall within 1 or two steps from where a picture of Earth would go rather than expressing the whole range of possibilities for even a single unknown dimension, of which there are currently 3). --AndrewBuck 02:38, 10 May 2007 (UTC)

• support idea. Allow for artistic freedom, provided the image has some real informative value.--Cyclopia 07:57, 10 May 2007 (UTC)

• I disagree with AndrewBuck's amputation of the his original idea. Rarity of a planet type is irrelevant; you are an individual and I would doubt that you would consider that meaningless. I am for as many dimensions are necessary to describe reality: It makes for less needless debate. - GabrielVelasquez (talk) 20:01, 30 December 2007 (UTC)

Great, I think we have enough support now. There is only one more roadblock to pass: How do we offically create this new project anyway? (and what will its name be?) Fusion7 00:31, 11 May 2007 (UTC)

• Boldy, here's a crack at it:
  WP:AST. Debivort
  01:05, 11 May 2007 (UTC)

• A new image is up for review at Wikipedia:WikiProject Astronomy/Image Review. Debivort 18:46, 12 May 2007 (UTC)

Diagram accuracy

AFAIK, Gliese 581 is a third the mass of the sun, and Gliese 581 c orbits at 1/14 AU, making this diagram misleading — Jack · talk · 18:51, Thursday, 26 April 2007

In what way? It is a graph of this so-called "habitable zone", marked up with some known planets. mdf 19:52, 26 April 2007 (UTC)

It's a crude diagram at best, and has been replaced by one that's a bit better. At least someone had the decency to do something about it, and not just complain. Esseh 00:28, 27 April 2007 (UTC)

Hey,

Bold claims need to be backed up by evidence and references. — Jack · talk

· 10:14, Friday, 27 April 2007

Although, I do feel the new diagram is a vast improvement of the original — Jack · talk · 13:11, Friday, 27 April 2007

Interesting. The current graph is based on the previous graph, but that graph has no references cited. I am particularly interested in the functional form of the width of this zone. The article on the habitable zone gives the center of the zone, but not the width (and my cursory inspection of the net isn't forthcoming; still looking). One begins to wonder about original research. mdf 14:13, 27 April 2007 (UTC)

More interesting. Habitable Zones around Main Sequence Stars, Kasting, Whitmire and Reynolds, 1993, Icarus 101, 108 (abstract only, http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993Icar..101..108K&db_key=AST&high=38e0b7728702974) says the width of these zones is a function of the type of planet and star. There may well need to be more than two dimensions for any purported graph, which is always a problem for two-dimensional displays :-/ mdf 14:50, 27 April 2007 (UTC)

Yet more interesting. http://www.geosc.psu.edu/~kasting/PersonalPage/Pdf/annurev_03.pdf Evolution of a Habitable Planet, Kasting, Catling, Annu. Review of Astronomy and Astrophysics, 2003, 41:429-63. See figure 5 (page 444) and compare to current graph, above. The width of the HZ is fixed on a log scale, and this is cited again by Early Type Stars: Most Favorable Stars for Astrometrically Detectable Planets in the Habitable Zone, Gould, Ford and Fischer, Astrophysical Journal, 591:L155-L158, 2003 July 10 (see http://www.journals.uchicago.edu/ApJ/journal/issues/ApJL/v591n2/17148/17148.web.pdf, page L156, left column at the top). The Wikipedia graph is using a pseudo-log scale on radius, but the width of this zone is clearly changing more than the scale. The case for original (or at least incorrect) research grows. mdf 15:08, 27 April 2007 (UTC)

I'm the one to blame for the "Mark II" image with the extended habitable zone. You're quite right - it should really be of constant width. My reasoning only went as far as "Gliese 581 c is in the habitable zone, so the habitable zone must extend to its position." I would only point out that this diagram was not intended to be an exact representation of reality. (Note that it shows Mercury and Pluto the same size - despite the logarithmic scale! ..well, that's amusing to me.) It's just a rough indication of the situation, hopefully human-parseable at a glance. Of course, if anyone more qualified is able to create a more accurate depiction, that would be great. - Ben Ram 15:21, 27 April 2007 (UTC)

You are as qualified as I: as long as they are backed with a reference, anyone can create the graphic. You probably can do the actual job better than me though. I'll try and dig up the Icarus article that seems to be at the bottom of all of this. It requires a trip to the super-secret eyes-only access astronomy library, at the top of a very tall tower, carefully guarded by vicious gargoyles. But I've done it before... mdf 16:38, 27 April 2007 (UTC)

For now, I've updated my version of the image to have a constant width habitable zone, which is hopefully a somewhat more accurate representation. It looks a litte TOO wide, though - perhaps it should be thinner all the way along? And what about that kink around Earth, does that really exist? - Ben Ram 23:53, 27 April 2007 (UTC)

Ben - Kudos again. I think it looks good. It probably is too wide, but then again, the planets aren't to scale - probably also the reason for the "kink". Actually, if we really wanted to do the whole damned thing over, perhaps a linear X-axis, in AU, or something, might make it easier to work with. That kinda-log scale sucks. Just a random thought. Esseh 23:59, 27 April 2007 (UTC)

I kinda like Ben Ram's version. I'm responsible for "Mark I", wherein I kept the width of the HZ the same and just extrapolated as best I could. (And I'm no graphic artist, either). I had missed that Gliese 581 was 1/3 the size, and went after 1/2 size. Ben Ram is quite right - this in no way, shape, or form is meant to be an accurate, to-scale model - nor was the original. The planet diameters are way out, not just with repsect to each other, but particularly with respect to the size of the stars involved. My impression was also that the graphic was just that - a visual representation easily graspable by the masses, showing approximate positions. As for the HZ, frankly I think the whole concept is ridiculous, as it depends on too many variables, not just temperature of the star and insolation at a given distance. If that insolation includes a large amount of X-rays, I'd say the HZ would be quite a bit narrower, and towards the outside. ... unless the atmosphere of the planet somehow bolcked them. ... and with a "greenhouse" atmosphere, the planet might well be further back... and so on. Admit it - even the original diagram was just a quick way of showing relative positions within which a planet might be habitable, and is very rough at best. Mars might be habitable with a thicker atmosphere, but is shown outside the HZ. Just some thoughts. ...and I think kudos are due to Ben Ram for his attempt, at least! Esseh 21:43, 27 April 2007 (UTC

Mountains, molehills and "artist's impressions"

Hi all. I must admit, the new "artist's impression" added to the tidal forces section is, IMHO, totally inappropriate. There is NO evidence that H₂O and CO₂ or any form of atmosphere are even present, let alone what form they might be in. Yet we have "artist's impressions" of oceans, ice caps, clouds... How about an "artist's impression" of a huge, barren, moon-like rock, pocked with craters, deadly hot and bathed in radiation on one side, and exposed to the vacuum of space on the other? The "impression" would be just as valid! The media love "artist's impressions" - good visuals for front pages and good backdrops behind immaculately-coiffed news anchors, but they have NO basis in reality. I humbly suggest that we either remove the ridiculously speculative "artist's impression" from "tidally locked", or at least expand the caption to:

Artist's impression of Gliese 581 c IF it has an atmosphere, and IF that atmosphere is thick, and IF it has water, and IF all that water is not frozen on the dark side...

... you get the idea. Esseh 16:57, 3 May 2007 (UTC)

I removed it. Michaelbusch 17:00, 3 May 2007 (UTC)

Thanks, Michael. Esseh 17:14, 3 May 2007 (UTC)

I think it would actually be interesting to have such artist's impressions based on different scientific hypotheses. But we should not give one particular interpretation a lot of weight only because it is the most appealing one. Aside from that, the image has an obnoxious copyright watermark.--

I disagree with all of you. It is true that they can not be proven. But it does not hurt the actual material of the article, and in my opinion, artists impressions make the article seam less overwhelming and easier to understand. I think that many people share the same opinion with me. Why would it be bad to include a rendering? Why can't we speculate? Is there some taboo against creating a mental image of Glisie 581 c? In fact, shows such as Alien Planet or The Future is Wild were complete speculation, but they were aired on educational stations. I can understand why someone would think what you do though. I just really think that artit's impressions make readers more likely to stay and read the article in depth instead of just clicking the back button. (they at least do so for me.) Fusion7 18:55, 5 May 2007 (UTC)

I agree with Fusion7. "Imression" already implies that the picture is not very accurate. But it gives some reference point from where the reader may start his/her own imagination. Temur 21:17, 5 May 2007 (UTC)

Ok - let's add this one, too. Then we can start a section on the life forms... like:

At right is an artist's impression of the likely appearance of the indigenous life-forms on Gliese 581 c. The greenish hue is due to the absorption of red light by the epithelium, and the epicanthic folds and dark pigmentation of the eyes are from constant squinting into a sun that's very close, always overhead and never sets.

Sorry - it just strikes me that this is supposed to be an encyclopedia, not a comic book. (And sorry again - this sounds a bit sarcastic, when it was meant to be mildly amusing. I think I'll call her Gillian...) Esseh 22:59, 5 May 2007 (UTC)

Where does the picture come from? If it is by a professional astronomical artist, there might be some justification. But if it's drawn by a random Wikipedian, then it's just

Well, the current picture is not good; it should include its sun, other planets, and stars, or it should show how the other planets and its sun appear seen from the surface of Gliese 581 c. Even the continents and landmasses are seen; while being too speculative, I think the current version gives the wrong impression that the picture is very accurate, almost like a photograph. . Temur 04:00, 6 May 2007 (UTC)

Well, the current image is definitely going anyway, as it's a clear copyright violation from www.exobank.fr.--Pharos 07:50, 6 May 2007 (UTC)

Removed. --Cyclopia 15:05, 6 May 2007 (UTC)

And even if it wasn't a copyvio, the website in question is just amateur art by a non-notable artist.

How do you know that it is a violation of Wikipedia's image policy? (I mean, Cyclopia is probably right, but the image is from Wikimedia Commons.) However, I can't argue with Cop 633's point. Mabye we can find another, valid, artist's impression Fusion7 16:27, 6 May 2007 (UTC)

According to

WP:OR#Original_images the prohibition against original work from random wikipedians doesn't apply to imagery. "Wikipedia editors are encouraged to take photographs or draw pictures or diagrams and upload them ... to illustrate articles. [I]mages generally do not propose unpublished ideas or arguments, the core reason behind the NOR policy. Also, ... there are relatively few publicly available images we can take and use. Wikipedia editors' pictures fill a needed role." Glycerinester

13:39, 7 May 2007 (UTC)

In that case, wouldn't all renderings of exosolar planets be violating Wikipedia's image policy? Also, your arguement using the sentence "Images generally do not propose unpublished ideas or arguments," is flawed. There is nothing in that sentence that singles out images created by wikipedians. Either that or you presented an incomplete arguement. Fusion7 00:21, 8 May 2007 (UTC)

The image looks fine to me. The yellow-brown color is just uncorrected red-dwarf light, and the "arguments and ideas" in the image are in plenty of secondary sources. Glycerinester 01:03, 8 May 2007 (UTC)

Cop 633. Glad you like Gillian... :) Obviously, I concur. Esseh 02:19, 8 May 2007 (UTC)

Might I suggest something like Wikipedia:WikiProject Dinosaurs/Image review, where images are reviewed for accuracy and quality before being used. Without it, there would be almost no illustrations for extinct animals. If we wait for an image to be released into the public domain by a professional artist, we may be waiting a long time. Wikipedian artists are capable of this sort of work, but any image by anyone is not article-worthy. --Aranae 02:31, 8 May 2007 (UTC)

Please let me know if a Astronomy Image Review page is set up - I'm active in the dino illustration world and would like to do astronomical representations if they are needed. Debivort 05:23, 8 May 2007 (UTC)

Well first of all, Gillian would be fine in the extraterrestrial life article -- if she improved it. Image:Gliese.JPG is already there, and linked from two other articles as well. This is the picture we're talking about, right?

According to

WP:WEIGHT

, although personally I don't see this particular image violating that one either. Not every editorial dispute gets settled by a policy clause.

Why don't we just hear why people do or don't want this particular picture in this particular article, instead of trying to rule it in or out of order on ad hoc technicalities? Glycerinester 13:27, 8 May 2007 (UTC)

I asked at the

Actually, I'd take it even further than Cop 633. With all due respect to Debivort and the Dino illustration group, they have skeletons (from which muscle size and attachment can be deduced) and extant reptiles and birds upon which to base illustrations. The only speculation would be, really, in skin and eye colour. To my knowledge, it is not yet known whether Gliese 581 c even has an atmosphere, let alone its composition (H₂O, CO₂, CH₄, or whatever), it's state (solid or liquid), or its distribution on the planet surface. On what do you base an illustration?

There is some evidence (within limits) as to the planet's size, for example, making the remaining image reasonable, in that it just depicts relative size compared to Earth. Similarly, the extrapolated view of Sol from Gliese 581 in the infobox can be deduced from known star positions. In neither of these is there a wildly speculative attempt to display the planet surface. So, some images are reasonable, as they are based on observations to date. Perhaps we should stick to ones like those? Esseh 13:43, 8 May 2007 (UTC)

P.S. The "hydrogen atom" example in "original images" really should be changed. Deuterium and tritium spring to mind... Esseh 13:43, 8 May 2007 (UTC)

> as far as I can tell, the notion that a red dwarf star would make a planet's atmosphere look yellow is speculation

The Sun has a surface temperature of 5785 K. Gliese 581 has a surface temperature of 3480 K. Find those two numbers on literally any of the google image results for "color temperature" to see the contrast in colors. This isn't speculative or OR or even controversial. What color illumination did you think would be realistic?

Nobody here wants "rubbish" in the article. Based on everybody's comments about Gliese.JPG here it sounded horrible. Then I saw it and I don't see what the fuss is about. It looks kinda big. It's got light blotches and dark blotches that could really be anything, even lunar maria. And it's lit correctly, which is more than you can say for this much more widely viewed image. In terms of educating people Gliese.JPG looks like a net plus. I thought you guys were talking about something like this. Glycerinester 14:19, 8 May 2007 (UTC)

In terms of educating people, Gliese.JPG looks like a net zero. I don't understand how can being "big and blotchy" useful for educating people. "Lit correctly" means nothing: by the same assumptions, Earth would have a distinct yellow-white hue of the atmosphere, while it is instead a blue-white hue, due to Rayleigh scattering (and since the background of Gliese.JPG is oddly brownish, the yellowish hue of the planet seems more an effect of it being an old daguerrotype for outer space :) ). Come on: we don't even still know if Gliese 581 c is a "rocky" or an "icy", nor what kind of atmosphere it has (I bet it's even hotter and thicker than that of Venus, and $DEITY only knows how it looks like -would you have predicted Titan from its size and distance from Sun?). I'm all for linking the image, and perhaps opening an "Artistic impressions" section could be even nice, but including the image has no educational value at all. --Cyclopia 17:18, 8 May 2007 (UTC)

I say it has less than net zero educational value. The image is strongly misleading and should not be included in the article. — JyriL ^talk 19:46, 8 May 2007 (UTC)

The image doesn't 'educate' at all, because it tells the viewer nothing that is known to be true. I actually think this image produced by the discoverers is better, not because it's perfect, but because it shows you things that we know are true: it shows you that the planet orbits a red star, that it's not a gas giant, and that there are other planets, gas giants, in the system. It's not ideal (the star looks lame, and the phase angle is wrong, and the atmosphere is speculative), but it's better pedagogically (the current Celestia image is better still, however).

Cop 633

21:29, 8 May 2007 (UTC)

I agree that this image is a better image than

User:Angr (here and here) because it wasn't "free" enough. Apparently, it seems that Image:Gliese.JPG was inteded to be some sort of replacement. And if that's the case, then perhaps the replacement itself was chosen incorrectly. Latitude0116

03:30, 9 May 2007 (UTC)

Correct lighting "means nothing" ... in astronomy? In the study of celestial light sources? In the Solar System everything has the same light source that we call white and render in artwork as white without having to think about it. As a result of billions of years of biology, the sun is white to us by definition. Some astronomers may want to call this color "yellow-white" and confuse everyone, but the color is quantifiable, it's 5785 K, and that's not disputed. Anything hotter than that is "bluer" and anything cooler is "redder," regardless of whether it's actually yellow or orange. These are not "assumptions," this is how it works.

Look, in this image we don't attribute the red color of the water in the image to some substance or scattering phenomenon in the water turning it red. Whether it's an unfiltered, uncorrected photo or whether the artist tampered with it for dramatic effect, either way the viewer understands the water is supposed to look red because it's supposed to look like it's lit with red light. If the camera were pointing in the opposite direction, away from the light source, the picture would still tell you what color the light source was supposed to be.

Similarly, there's no reason to attribute the color in Image:Gliese.JPG to the object instead of the light. It's not yellow in most places and white in a few others. The yellow color is the white point in the image. Gliese.JPG is the one showing you the known color of the star, which is not either of the colors in the ESO image, which are far too red on the one hand and far too white on the other, and extra-wrong because the white light is clearly coming from some unseen second source. The ESO image thus shows us multiple things that are known to be false.

Gliese.JPG avoids the scorn I would direct toward an image portraying some baseless speculation -- like a human-habitable surface -- because by its very vagueness it simultaneously illustrates a number of the different possibilities. In the image we can imagine a Venus-like surface under layers of clouds, if we want, or interpret the white band around the right limb of the globe as a surface feature, the visible fringe of the huge dark-side ice cap of a tide-locked, nearly airless rock. (It doesn't show a Venus-like uniform cloud cover, which would be boring and wouldn't effectively distinguish the object from a gas giant.)

All I can really tell from looking at the object in Gliese.JPG is it's orbiting a red star -- a real one, not a cartoon -- and it's not a gas giant, and other than that it could be almost anything. Just like the real object. Glycerinester 03:36, 9 May 2007 (UTC)

I'm aware of that. What I wanted to say was different. --Cyclopia 12:52, 9 May 2007 (UTC)

Yes, but what's the origin the colour of the light source? That's the problem. We know for sure that something lighted by Gl581 has a redder hue than the same objected lighted by the Sun. But what's the actual colour of the object? Again: the red sunset you show tell us how wrong can be assumptions made only on the basis of the star color, because that sunset is surely not red just because of the star being red! I have no idea about how scattering/dust in the atmosphere/etc. may actually paint Gl581 c. --Cyclopia 12:52, 9 May 2007 (UTC)

No, it's showing something of a given color. If you want to show the known color of the star, show the star itself. --Cyclopia 12:52, 9 May 2007 (UTC)

No, you can't tell it's orbiting a red star, unless you know the actual colour of the surface in white light. If I'd show you a Titan and a Mars image, under the same assumptions you would think they orbit a red star (and maybe Uranus a blue one?), but they do not. The facts are: Gliese.JPG is mere speculation. Gliese.JPG may be depicting practically anything. It has no intrinsic informative value. --Cyclopia 12:52, 9 May 2007 (UTC)

Maybe this is some new wikicustom I'm not aware of, but last time I checked it wasn't cool to break up somebody else's post and sign the extra pieces for them. Glycerinester 04:41, 10 May 2007 (UTC)

I was just mimicking email-like style of answering your points one by one. Answering all your post in a single batch would have been barely readable (as your re-format shows). Since it's a discussion, I thought in good faith that it was better this way. However, do as you please, what is important is that the message passes. :) --Cyclopia 08:57, 11 May 2007 (UTC)

And you could tell a gas giant from a rock, at that distance, if it had a "boring" cloud cover like Venus? The image still gives the ("artistic") impression of an atmosphere that is not known to be there. Why not a moon-like rock (or ice ball, for that matter) surface, reflecting nice gray, or ice-blue (or ice-orange, with a red sun) surface? It's not the image, per se that bothers me, but the implied knowledge that's just not there. Your "red suset" pic is beautiful, I admit. And its at least potentially a realistic view of a sunset on Sol 3 (d?). So, what colour would it be at that same angle without an ocean to reflect it? Without an atmosphere to refract it? With an atmosphere of different density or composition? With no atmosphere? Would it look the same? How about at a different angle? I rather doubt it. (Sorry, I'm tired and starting to sound sarcastic again - without meaning it. Gillian and I are going to bed.) Esseh 04:01, 9 May 2007 (UTC) P.S. And I didn't indent any more.... the discussion (one of the best I've had, frankly) was in danger of disappearing over the event horizon :) Esseh 04:01, 9 May 2007 (UTC)

> And you could tell a gas giant from a rock, at that distance, if it had a "boring" cloud cover like Venus?

Er, no, we could not. That's what I said. That's why it would have been a bad choice.

> Why not a moon-like rock (or ice ball, for that matter) surface, reflecting nice gray, or ice-blue ... surface?

As far as I can tell, maybe that's what it is. With the white balance corrected for the light source, the surface is mostly desaturated, i.e. grey or white. (A little bit pinkish but that's not necessarily intentional.) It could be clouds or ice or grey rock. I can't tell what it is. Glycerinester 08:26, 9 May 2007 (UTC)

Perhaps this image would be suitable, but may need to be altered by another Wikipedian because the lighting around the edge of the planet is off. Latitude0116 04:20, 9 May 2007 (UTC)

Is it just me or does

look like Mars? Sagittarian Milky Way 05:07, 9 May 2007 (UTC)

The yellow planet image is terribly misleading, it looks like Tatooine. Blue one looks like... frozen Tatooine. The ESO image is similarly wrong (plus the planets have wrong sizes). Given the fact that it is most likely either a super-Venus, a super-hot ocean planet, or a mini-sized gas giant, its surface should not be visible under the cloud layers. The background is way too full of stars etc. We should avoid misleading artistic impressions and stick on informative graphs if possible. We know too little about this planet for a good artistic impression. — JyriL ^talk 15:10, 9 May 2007 (UTC)

Listen, my point is that we going by the standards given by the other posters, we might as well delete every impression. Either this image is spared, or all images of exosolar planets are deleted. We have little evidence for any of them. Besides, it adds flavor to the article. Fusion7 21:25, 9 May 2007 (UTC)

Not at all. The Celestia picture, for example, makes complete sense. It is an actual computer simulation of the system, and shows how the sky would actually look like from Gl581c. The sizes of the planet and of the star are with good approximation correct. Other impressions that at least try to show something that we know it's true: the star and its distance from the planet, the other planets in the system, etc. If the planet depicted in Gliese.JPG was part of a larger scene showing these things, I would have agreed on leaving it. But alone as it is, it is just a sand-coloured globe. It is a pretty picture, really, and I like it, but it has no meaning at all. --Cyclopia 21:57, 9 May 2007 (UTC)

Fusion7 is correct that there are some very outrageous examples in other articles; look at this so-called 'possible aspect' (?!) of Mu Arae d [15]. I say nuke it and all its ilk. But the reason people are so fixated on this image is that Gliese 581 c has hit the headlines, and thus this page will have a lot of traffic, so it's important that we agree on some standards here before reaching for the flamethrowers in a systematic way.

Cop 633

22:05, 9 May 2007 (UTC)

Well, If you read the topic below, you will see that there is finally an end in site to this artist's impressions crisis. (Well, it would be fun giving this conflict a name.) The major people from both sides have agreed on Debivort/AndrewBuck have proposed. At last we can return to our Myspace accounts or World of Warcraft characters without fear of returning to find that our edits involving the images of exosolar plants were only to be undone by someone from the opposite side. :) Fusion7 00:40, 11 May 2007 (UTC)

(Travel time) 8 Million Years?

I'm just curious where this number came from, since it is uncited. On surface level, it smacks of being a back-of-envelope calculation based on old probe velocities, which are not as efficient as newer systems. I may try to look up some information in a few books I know of (but don't have with me at present) to track down citeable information, since Gliese 581 was being looked at as a star of interest a couple decades ago. The Dark 18:27, 27 April 2007 (UTC)

It's also ignoring the obvious fact that even the old probes were not designed for maximum solar system escape velocity, they were designed for visiting the planets, and they have a totally different trajectory because of that. I think that any estimation of travel time "with current propulsion technology" is fairly meaningless, not only because specific mechanisms that could work in such a mission are currently only theoretical (even if using fairly off-the-shelf technology), but also of course because if any space agency were to pursue such a mission they would certainly take at least 20 years to develop new technology.--Pharos 19:03, 27 April 2007 (UTC)

We don't have the technology needed nor we don't know when it will become available. Any speculation about sending probes there should be mercilessly removed.— JyriL ^talk 22:49, 27 April 2007 (UTC)

"Go there"

There should be some discussion of the realistic possibilities of sending a probe and of manned travel. As far as I can tell based on a quick reading of Interstellar travel, the best chance for a probe which doesn't require a breakthrough in fusion power would be ground-based lasers powering sails - from the article there, it might eventually get up to around 10% of lightspeed. Thus, counting construction and acceleration time, arrival would be 2 to 3 centuries from now. As for getting humans there, without a major rewrite in the laws of physics (and wormholes, though allowed by relativity, would definitely constitute such a rewrite), a fusion- or other energy-related breakthrough is essentially required, as well other major breakthroughs in biology and chemistry to keep the colonists fed, and even then the effort required to build such a ship is measured in years of world GDP, and the travel time in centuries. I'd add the 2 to 3 centuries figure to the article, but it's pretty much OR - can anyone get a citation for something like this? --72.252.40.68 20:02, 25 April 2007 (UTC)

I'd prefer to state something to the effect of "with our best current technological ability, it would require several hundred light years to send humans or even unmanned probes." Nothing more needs to be said. Egumtow 20:15, 25 April 2007 (UTC)

You mean years, not light years. I actually added a section which says a bit more than that. If you edit it down, at least preserve the links to interstellar travel and to spacecraft propultion. --72.252.40.68 20:34, 25 April 2007 (UTC)

I didn't edit it at all. Perhaps someone else? Egumtow 21:24, 25 April 2007 (UTC)

Actually, there should be no such discussion at this article. Do we have a discussion of the chemistry of paper manufacturing at toilet paper? I'm not even sure that there is a need for a wikilink to interstellar travel. The article is about a planet, not speculative star-ship engineering and the difficulties thereof. My advice: trust the reader to have a brain and the necessary curiosity to find out about that kind of thing on their own. Focus on the subject. mdf 20:46, 25 April 2007 (UTC)

I agree, the section on "Difficulty of exploration" is not relevant and should be removed. Its gee-whiz cool but not directly relevant. Maybe a see also link referencing interstellar travel? Rich.lewis 21:13, 25 April 2007 (UTC)

Agreed. Egumtow 21:25, 25 April 2007 (UTC)

Devil's advocate: A "see also" would require a significant amount of reading (and calculation) to extract the data presented here succinctly. This is obviously the only known candidate for interstellar travel at this time, and thus this data is far more salient than the analogy of toilet paper - it is as if toilet paper was the ONLY practical use for paper, in which case a brief section which extracted the relevant data WOULD be appropriate. And does anyone doubt that potential citations for this section will abound - that as soon as some good scientist has made a quote that treats the matter succinctly, that quote will show up in all the slower-news-cycle stories on this? (the NYT "go there" quote discussed above is a start - this section does need a cited opener of "The possibility that this planet may have, or be able to support, life, has triggered some speculation over a mission to go there" or something.)

Also, I bet you folks have enough background knowledge to have already more-or-less known the data in this section. Consider that there are a LOT of wikipedia users who probably don't have a sense of the scale of undertaking that a probe or ship would mean. Imagine you didn't know this - wouldn't this data seem pertinent here? --72.252.40.68 22:03, 25 April 2007 (UTC)

For the record

The section had started to wander, and was blanked citing

Interstellar travel has never been attempted, and presents several serious technical hurdles. Given the means of spacecraft propulsion which are currently believed possible, any practical spacecraft would travel at a fraction of the speed of light, and thus would take many years to reach this planet. For instance, a small probe travelling at ten percent of the speed of light would take over two hundred years. The possibility of a manned expedition or colonization, on the other hand, cannot even be contemplated with today's technology. REF The larger ship needed would be even slower, and would require additional breakthroughs in many fields for propulsion and for the survival needs of its passengers, both en route and on arrival. /REF

(those REFs should be converted to tags.) —The preceding

I'm not surprised the section was removed. I am, however, disappointed it was added back, as it will remain a perpetual magnet for further original research and crystal-balling. That it contributes no further information about the subject of this article strongly suggests that the

clusterfucks. mdf

12:00, 26 April 2007 (UTC)

The view you're taking if what they call "scientific", not "encyclopedic" or "encylopedic" by your words. If we edit in Wikipedia, we have to act like idiots. That's something I figured out after a few months' dispute.

heru|nar

12:35, 26 April 2007 (UTC)

I disagree that this is the only candidate for interstellar travel. The nearest star which is in any way interesting would be a candidate for a probe to be sent there to transmit back information about the planets if any. A see also direected to

WP:A and allow inclusion here- when and if such comments are printed. Edison

14:07, 26 April 2007 (UTC)

I just checked articles for Alpha Cen, Epsilon Eri, Wolf 359, Barnard's Star, and 61 Cyg, all of which are closer than Gliese 581, and there is no mention of interstellar travel in any of those articles, as I believe is proper. There is no need to mention it here, either. That stuff belongs in articles like Interstellar travel. Vegasprof 21:31, 30 April 2007 (UTC)

Well, it appears you did not read Barnard's Star, at least, very carefully.--Pharos 21:34, 30 April 2007 (UTC)

Oops.  :-) Well, it's only once small reference; I don't know how I missed it. (I also missed the one at Alpha Centauri.) Gliese 581 is more than three times as far away as Barnard's Star. If there is a paper out there, written by responsible people mentioning the possibility of travel to Barnard's Star, then it's ok, otherwise, it isn't. I still stand by my opinion. "Going there" is a highly speculative thing, and should not be mentioned in the article on any astronomical body, cluster, or whatever, unless some notable group is actually studying the possibility. Vegasprof 23:03, 30 April 2007 (UTC)

There's a whole section on it at Barnard's Star, actually. There is no longer any such section as 'Going there' in our Gliese 581 c article, just one line in a section on 'Further study' (which includes future telescopic study), which I think is justified by the issue being raised by multiple astronomers. The reason such a possibility is more notable for Gliese 581 than for just any nearby star is of course because of the possible presence of an earthlike planet (this is the same reason that Barnard's Star was discussed in this context in the past).--Pharos 00:13, 1 May 2007 (UTC)

If NASA can be believed, we'll be going back to the Moon, Mars, etc, before we go to Europa. The same will happen with interstellar: low hanging fruit will be taken first. As for the proposals: Daedalus is completely impractical as of now, even if we somehow could build the machine (which we can't). LongShot is more feasible, but even if launched tomorrow, no one editing Wikipedia today will be alive to see results (if any; simple survival is a big question at these time-scales). I agree with Vegasprof and others: this kind of stuff is reasonable for interstellar travel, with links to possible targets from there to here. But back-links from here to there are not warranted, until starships become a viable means of transportation. The database should be structured according to current knowledge, not speculation to future events however well "reliably" reported such speculation may be. mdf 20:40, 1 May 2007 (UTC)

I absolutely agree that there should be no long discussion of ways of sending a probe through interstellar space in the main article for a given planet or star of interest. A brief link to the

WP:IDONTLIKEIT and is an invalid basis for deleting text. For an analysis of the eneregy requirement and gaps between present and required technology for an interstellar probe, in a paper presented at the 46th International Astronautical Congress, October 1995, Oslo, Norway by Geoffrey A. Landis (physicist and part-time science fiction writer), Ohio Aerospace Institute, NASA Lewis Research Center, see [17]. There are bound to be more recent such papers out there. Edison

22:27, 1 May 2007 (UTC)

Just to clarify my agreement with

Solar system, objects where missions have taken place or are planned, a section on "going there" is much more appropriate. I think this solution should be acceptable. Vegasprof

00:05, 2 May 2007 (UTC)

Indeed, Vegasprof, I quite agree with your sentiment. I was the person who reduced the "going there" discussion, which was formerly a whole section, to just one sentence.--Pharos 14:36, 3 May 2007 (UTC)

I have a question...

Yes. The planet Earth is near to its end (look at the news) scientist have had found a brand new planet to destroy. To put it clear the whole affair, why are we talking of colonization? Apart technical datas, is this trip really necessary? --87.19.131.136 13:48, 27 April 2007 (UTC)

Yeah, that's exactly what scientists are talking about all right. --NEMT 14:19, 27 April 2007 (UTC)

Was my joke (here in the discussion section) about building a starship considered vandalism? I hope not. I was half serious (even scientists should dream) and half teasing. Humor has it's place in the Universe.

I hope we get to Gliese 581 c someday. Paradigms were made to be broken.

Sean7phil 05:11, 26 April 2007 (UTC)

HUGE one has obviously taken place...What should we do? HaLoGuY007 21:43, 25 April 2007 (UTC)

It's gone... HaLoGuY007 21:45, 25 April 2007 (UTC)

All changes on Wikipedia are easily reversible. If you spot vandalism in the future, feel free to

Undo it. Adam McMaster

21:48, 25 April 2007 (UTC)

No, the article said WTF (without being abbreviated) about 3,000 times. The whole article was gone. I think something was wrong with my computer, because I came back after two seconds and the article (which I had never seen before) was there. HaLoGuY007 20:43, 26 April 2007 (UTC)

Bear in mind that there are goodness knows how many users logged on at a time. Vandalism is common on easily reached articles, but if a vandal can reach it easily, so can everyone else. Two seconds is all it takes to revert a change.

Man

06:42, 27 April 2007 (UTC)

I'm new, I had no clue what to do. Thanks for the information though, because it actually was kind of weird. Thanks.

I would like to take up the challenge of sorting these 58 entries into an organized format, consolidating related and redundant entries that have been dispursed throughout. Hopefully this will not be viewed as vandalism as nothing will be deleted in that process. I think the article index itself is a good format, having only 8 main points. If anyone disagrees with the move of their remarks feel free to re-place them under the appropriate heading/subheading.

1 Discovery
2 Physical characteristics
2.1 Mass
2.2 Radius
2.3 Age
2.4 Orbit
3 Climate and habitability
3.1 Temperature
3.1.1 Derivation
3.2 Liquid water
3.3 Tidal forces
3.3.1 Tidal lock
3.3.2 Theoretical models
3.4 Greenhouse effect
4 Further study
5 See also
6 References
7 Selected media articles
8 External links

- GabrielVelasquez (talk) 20:45, 29 December 2007 (UTC)

That structure looks like a good way to organize the data.--Marhawkman (talk) 21:57, 29 December 2007 (UTC)

THANK YOU for your support: The full sort is in progress, though it had a temporary set back (dino-lover got jumpy), and is almost done. - The Goal is to get it down from 58 random and redundant entries to 19 or so logical and well structured headings. I've been on line for almost 13 hours now and I may have to finish tomrrow. -GabrielVelasquez (talk) 05:11, 30 December 2007 (UTC)

This is a work in progress, trust me the duplicate numbers are only for the sort and will be removed ASAP. The normal numbering on the menu will take over and it will look great. -GabrielVelasquez (talk) 05:42, 30 December 2007 (UTC)

The comment(s) below were originally left at Talk:Gliese 581c/Comments, and are posted here for posterity. Following