Ring system
A ring system is a disc or ring, orbiting an astronomical object, that is composed of solid material such as dust and moonlets, and is a common component of satellite systems around giant planets like Saturn. A ring system around a planet is also known as a planetary ring system.[1]
The most prominent and most famous planetary rings in the
Evidence suggests that ring systems may also be found around other types of astronomical objects, including moons, brown dwarfs, and other stars.Formation
There are three ways that thicker planetary rings have been proposed to have formed: from material originating from the
Fainter planetary rings can form as a result of meteoroid impacts with moons orbiting around the planet or, in the case of Saturn's E-ring, the ejecta of cryovolcanic material.[5][6]
Ring systems may form around
Ring systems of planets
The composition of planetary ring particles varies, ranging from silicates to icy dust. Larger rocks and boulders may also be present, and in 2007 tidal effects from eight moonlets only a few hundred meters across were detected within Saturn's rings. The maximum size of a ring particle is determined by the specific strength of the material it is made of, its density, and the tidal force at its altitude. The tidal force is proportional to the average density inside the radius of the ring, or to the mass of the planet divided by the radius of the ring cubed. It is also inversely proportional to the square of the orbital period of the ring.
Some planetary rings are influenced by shepherd moons, small moons that orbit near the inner or outer edges of a ringlet or within gaps in the rings. The gravity of shepherd moons serves to maintain a sharply defined edge to the ring; material that drifts closer to the shepherd moon's orbit is either deflected back into the body of the ring, ejected from the system, or accreted onto the moon itself.
It is also predicted that
Jupiter
Jupiter's ring system was the third to be discovered, when it was first observed by the Voyager 1 probe in 1979,[10] and was observed more thoroughly by the Galileo orbiter in the 1990s.[11] Its four main parts are a faint thick torus known as the "halo"; a thin, relatively bright main ring; and two wide, faint "gossamer rings".[12] The system consists mostly of dust.[10][13]
Saturn
Saturn's rings are the most extensive ring system of any planet in the Solar System, and thus have been known to exist for quite some time. Galileo Galilei first observed them in 1610, but they were not accurately described as a disk around Saturn until Christiaan Huygens did so in 1655.[14] The rings are not a series of tiny ringlets as many think, but are more of a disk with varying density.[15] They consist mostly of water ice and trace amounts of rock, and the particles range in size from micrometers to meters.[16]
Uranus
Uranus's ring system lies between the level of complexity of Saturn's vast system and the simpler systems around Jupiter and Neptune. They were discovered in 1977 by
of Uranus.Neptune
The system around Neptune consists of five principal rings that, at their densest, are comparable to the low-density regions of Saturn's rings. However, they are faint and dusty, much more similar in structure to those of Jupiter. The very dark material that makes up the rings is likely organics processed by radiation, like in the rings of Uranus.[20] 20 to 70 percent of the rings are dust, a relatively high proportion.[20] Hints of the rings were seen for decades prior to their conclusive discovery by Voyager 2 in 1989.
Rings systems of minor planets and moons
Reports in March 2008 suggested that Saturn's moon Rhea may have its own tenuous ring system, which would make it the only moon known to have a ring system.[21][22][23] A later study published in 2010 revealed that imaging of Rhea by the Cassini spacecraft was inconsistent with the predicted properties of the rings, suggesting that some other mechanism is responsible for the magnetic effects that had led to the ring hypothesis.[24]
Prior to the arrival of New Horizons, some astronomers hypothesized that Pluto and Charon might have a circumbinary ring system created from dust ejected off of Pluto's small outer moons in impacts. A dust ring would have posed a considerable risk to the New Horizons spacecraft.[25] However, this possibility was ruled out when New Horizons failed to detect any dust rings around Pluto.
Chariklo
Chiron
A second centaur, 2060 Chiron, has a constantly evolving disk of rings.[27][28][29] Based on stellar-occultation data that were initially interpreted as resulting from jets associated with Chiron's comet-like activity, the rings are proposed to be 324±10 km in radius, though their evolution does change the radius somewhat. Their changing appearance at different viewing angles can explain the long-term variation in Chiron's brightness over time.[28] Chiron's rings are suspected to be maintained by orbiting material ejected during seasonal outbursts, as a third partial ring detected in 2018 had become a full ring by 2022, with an outburst in between in 2021.[30]
Haumea
A ring around Haumea, a dwarf planet and resonant Kuiper belt member, was revealed by a stellar occultation observed on 21 January 2017. This makes it the first trans-Neptunian object found to have a ring system.[31][32] The ring has a radius of about 2,287 km, a width of ≈70 km and an opacity of 0.5.[32] The ring plane coincides with Haumea's equator and the orbit of its larger, outer moon Hi’iaka[32] (which has a semimajor axis of ≈25,657 km). The ring is close to the 3:1 resonance with Haumea's rotation, which is located at a radius of 2,285±8 km.[32] It is well within Haumea's Roche limit, which would lie at a radius of about 4,400 km if Haumea were spherical (being nonspherical pushes the limit out farther).[32]
Quaoar
In 2023, astronomers announced the discovery of a widely separated ring around the dwarf planet and Kuiper belt object Quaoar.[33][34] Further analysis of the occultation data uncovered a second inner, fainter ring.[35]
Both rings display unusual properties. The outer ring orbits at a distance of 4,057±6 km, approximately 7.5 times the radius of Quaoar and more than double the distance of its Roche limit. The inner ring orbits at a distance of 2,520±20 km, approximately 4.6 times the radius of Quaoar and also beyond its Roche limit.[35] The outer ring appears to be inhomogeneous, containing a thin, dense section as well as a broader, more diffuse section.[34]
Rings around exoplanets
Because all
Fomalhaut b was found to be large and unclearly defined when detected in 2008. This was hypothesized to either be due to a cloud of dust attracted from the dust disc of the star, or a possible ring system,[38] though in 2020 Fomalhaut b itself was determined to very likely be an expanding debris cloud from a collision of asteroids rather than a planet.[39] Similarly, Proxima Centauri c has been observed to be far brighter than expected for its low mass of 7 Earth masses, which may be attributed to a ring system of about 5 RJ.[40]
A sequence of occultations of the star
Visual comparison
See also
References
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- ^ Leah Crane (Feb 18, 2023). "Weird dust ring orbits the sun alongside Mercury and we don't know why". New Scientist.
- ^ "Saturn's Rings May Be Old Timers". NASA (News Release 2007-149). December 12, 2007. Archived from the original on April 15, 2008. Retrieved 2008-04-11.
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- ^ "Historical Background of Saturn's Rings". www.solarviews.com. Archived from the original on 2012-05-10. Retrieved 2016-06-15.
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- ^ Porco, Carolyn. "Questions about Saturn's rings". CICLOPS web site. Archived from the original on 2012-10-03. Retrieved 2012-10-05.
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- ^ "NASA - Saturn's Moon Rhea Also May Have Rings". Archived from the original on 2012-10-22. Retrieved 2010-09-16. NASA – Saturn's Moon Rhea Also May Have Rings
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Jones, G. H.; et al. (2008-03-07). "The Dust Halo of Saturn's Largest Icy Moon, Rhea". Science. 319 (5868): 1380–1384. S2CID 206509814.
- Planetary Society. Archivedfrom the original on 2008-06-26. Retrieved 2008-03-09.
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Steffl, Andrew J.; Stern, S. Alan (2007). "First Constraints on Rings in the Pluto System". The Astronomical Journal. 133 (4): 1485–1489. S2CID 18360476.
- ^ "Surprise! Asteroid Hosts A Two-Ring Circus Above Its Surface". Universe Today. March 2014. Archived from the original on 2014-03-30.
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- ^ Devlin, Hannah (8 February 2023). "Ring discovered around dwarf planet Quaoar confounds theories". The Guardian. Archived from the original on 8 February 2023. Retrieved 8 February 2023.
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Hilke E. Schlichting, Philip Chang (2011). "Warm Saturns: On the Nature of Rings around Extrasolar Planets that Reside Inside the Ice Line". S2CID 42698264.
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- ^ Rachel Feltman (2015-01-26). "This planet's rings make Saturn look puny". The Washington Post. Archived from the original on 2015-01-27. Retrieved 2015-01-27.
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External links
- USGS/IAU Ring and Ring Gap Nomenclature
- Everything a Curious Mind Should Know About Planetary Ring Systems with Dr Mark Showalter, Bridging the Gaps: A Portal for Curious Minds
- Physical Chemistry of Evolution of Planetary Systems
- Gladyshev G. P. Thermodynamics and Macrokinetics of Natural Hierarchical Processes, p. 217. Nauka, Moscow, 1988 (in Russian).