Planetary surface
A planetary surface is where the solid or liquid material of certain types of
In
Planetary surfaces and surface life are of particular interest to
Indirect observations by flyby or orbit currently provide insufficient information to confirm the composition and properties of planetary surfaces. Much of what is known is from the use of techniques such as
Distribution and conditions
Planetary surfaces are found throughout the
Exploration
Distance, gravity, atmospheric conditions (extremely low or extremely high
Past missions
This section needs additional citations for verification. (September 2020) |
The first extraterrestrial planetary surface to be explored was the
There have been many failed attempts, more recently Fobos-Grunt, a sample return mission aimed at exploring the surface of Phobos.
-
Venus).[4]
Forms
The surfaces of Solar System objects, other than the four
In general terrestrial planets have either surfaces of ice, or surface crusts of rock or regolith, with distinct terrains. Water ice predominates surfaces in the Solar System beyond the frost line in the Outer Solar System, with a range of icy celestial bodies. Rock and regolith is common in the Inner Solar System until Mars.
The only Solar System object having a mostly liquid surface is Earth, with its global
Liquid water as surface, beside on Earth, has only been found, as seasonal flows on warm Martian slopes, as well as past occurrences, and suspected at the habitable zones of other planetary systems. Surface liquid of any kind, has been found notably on Titan, having large methane lakes, some of which are the largest known lakes in the Solar System.
Volcanism can cause flows such as lava on the surface of geologically active bodies (the largest being the Amirani (volcano) flow on Io). Many of Earth's Igneous rocks are formed through processes rare elsewhere, such as the presence of volcanic magma and water. Surface mineral deposits such as olivine and hematite discovered on Mars by lunar rovers provide direct evidence of past stable water on the surface of Mars.
Apart from water, many other abundant surface materials are unique to Earth in the Solar System as they are not only
Extraterrestrial Organic compounds
Increasingly organic compounds are being found on objects throughout the Solar System. While unlikely to indicate the presence of extraterrestrial life, all known life is based on these compounds. Complex carbon molecules may form through various complex chemical interactions or delivered through impacts with small solar system objects and can combine to form the "building blocks" of Carbon-based life. As organic compounds are often volatile, their persistence as a solid or liquid on a planetary surface is of scientific interest as it would indicate an intrinsic source (such as from the object's interior) or residue from larger quantities of organic material preserved through special circumstances over geological timescales, or an extrinsic source (such as from past or recent collision with other objects).[6] Radiation makes the detection of organic matter difficult, making its detection on atmosphereless objects closer to the Sun extremely difficult.[7]
Examples of likely occurrences include:
- Tholins – many Trans Neptunian Objects including Pluto-Charon,[8] Titan,[9] Triton,[10] Eris,[11] Sedna,[12] 28978 Ixion,[13] 90482 Orcus,[14] 24 Themis[15][16]
- Comet 67P
On Mars
Martian exploration including samples taken by on the ground rovers and spectroscopy from orbiting satellites have revealed the presence of a number of complex organic molecules, some of which could be biosignatures in the search for life.
- Thiophene (C
4H
4S)[17] - Polythiophene (polymer of C
4H
4S)[18] - Methanethiol (CH
3SH)[19] - Dimethyl sulfide (CH
2S)[19]
On Ceres
- Ammonium bicarbonate (NH
4HCO
3).[20][21] - Gilsonite[22]
On Enceladus
- CH3 NH2)
- CHO)
On Comet 67P
The space probe Philae (spacecraft) discovered the following organic compounds on the surface of Comet 67P:.[24][25][26]
- Acetamide (CH
3CONH
2) - Acetone (CH3)2CO
- Methyl isocyanate (CH
3NCO) - Propionaldehyde (CH
3CH
2CHO)
Inorganic materials
The following is a non-exhaustive list of surface materials that occur on more than one planetary surface along with their locations in order of distance from the Sun. Some have been detected by spectroscopy or direct imaging from orbit or flyby.
- Silicate rock – Mercury, Venus, Earth, Mars, asteroids, Ganymede, Callisto, Moon, Triton
- Regolith – Mercury;[32] Venus,[33] Earth-Moon system; Mars (and its moons Phobos and Deimos); asteroids (including 4 Vesta[34]); Titan
- Nitrogen ice (N) – Pluto–Charon,[35] Triton,[36] Kuiper belt objects, Plutinos
- Sulphur(S) – Mercury; Earth; Mars; Jupiter moons – Io and Europa
Rare inorganics
- Salts – Earth, Mars, Ceres, Europa and Jupiter Trojans,[37] Enceladus[38]
- Clays – Earth; Mars;[39] asteroids including Ceres[40] and Tempel 1;[41] Europa[42]
- Sand – Earth, Mars, Titan
- Calcium carbonate (CaCO
3) – Earth, Mars[43][44] - Sodium carbonate (Na
2CO
3) – Earth, Ceres[45][46][47]
Carbon Ices
- Carbon monoxide ice (CO) - Triton[51]
Landforms
Common rigid surface features include:
- Impact craters (though rarer on bodies with thick atmospheres, the largest being Hellas Planitia on Mars)
- Dunes as found on Venus, Earth, Mars and Titan
- cryovolcanoes
- Rilles
- Mountains (the highest being Rheasilvia on 4 Vesta)[citation needed]
- Escarpments
- Canyons and valleys (the largest being Valles Marineris on Mars)
- Caves
- Lava tubes, found on Venus, Earth, The Moon and Mars
Surface of gas giants
Normally, gas giants are considered to not have a surface, although they might have a solid core of rock or various types of ice, or a liquid core of metallic hydrogen. However, the core, if it exists, does not include enough of the planet's mass to be actually considered a surface. Some scientists consider the point at which the atmospheric pressure is equal to 1 bar, equivalent to the atmospheric pressure at Earth's surface, to be the surface of the planet,[1] if the planet has no clear rigid terrain. Therefore the location of the surface of terrestrial planets do not depend on an atmospheric pressure of 1 Bar, even if for example Venus has a thick atmosphere with pressures at Venus's surface increasing well above Earth's atmospheric pressure.
Life
Planetary surfaces are investigated for the presence of past or present extraterrestrial life. Thomas Gold expanded the field by advancing the possibility of life and a so-called deep biosphere below the surface of a celestial body, and not only on the surface.[53]
Surface chauvinism and surfacism
Furthermore, Thomas Gold has criticized science which only focuses on the surface and not below in its search of life as surface chauvinism.[53]
Similarly the focus on surface bound and territorial
Gallery
-
The dry, rocky and icy surface of planet Mars (photographed by Viking Lander 2, May 1979) is composed of iron-oxide rich regolith
-
Pebbled plains of Saturn's moonHuygens probe, January 14, 2005) composed of heavily compressed states of water ice. This is the only ground-based photograph of an outer Solar System planetary surface
-
Surface of comet Tempel 1 (photographed by the Deep Impact probe), consists of a fine powder of contains water and carbon dioxide rich clays, carbonates, sodium, and crystalline silicates.
See also
- Extraterrestrial atmosphere
- Hydrosphere
- Subsurface ocean
- Ocean world
- Planetary radius
- Planetary geoid
References
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McKinnon, William B.; Kirk, Randolph L. (2007). "Triton". In Lucy Ann Adams McFadden; Lucy-Ann Adams; Paul Robert Weissman; Torrence V. Johnson (eds.). Encyclopedia of the Solar System (2nd ed.). Amsterdam; Boston: Academic Press. pp. 483–502. ISBN 978-0-12-088589-3.
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