Enceladus

Enceladus
Enceladus imaged by the Cassini orbiter, October 2015[a]
Discovery
Discovered byWilliam Herschel
Discovery dateAugust 28, 1789[1]
Designations
Designation
Saturn II
Pronunciation/ɛnˈsɛlədəs/[2]
Named after
Ἐγκέλαδος Enkélados
AdjectivesEnceladean /ɛnsəˈleɪdiən/[3][4]
Orbital characteristics
238037 km[5]
Eccentricity0.0047[5][6]
1.370218 d[5]
Inclination0.009° (to Saturn's equator)[5]
Satellite ofSaturn
Physical characteristics
Dimensions513.2 × 502.8 × 496.6 km[5][7]
Mean radius
252.1±0.2 km[7][8] (0.0395 Earths, 0.1451 Moons)
Mass(1.080318±0.00028)×1020 kg[8] (1.8×10−5 Earths)
Mean density
1.6097±0.0038 g/cm3[8]
Surface gravity
0.113 m/s2 (0.0116 g)
Moment of inertia factor
0.3305±0.0025[9]
0.239 km/s (860.4 km/h)[5]
Synodic rotation period
Synchronous
< 0.05°[10]
Albedo1.375±0.008 (geometric at 550 nm)[11] or 0.81±0.04 (Bond)[12]
Surface temp. min mean max
Kelvin[13] 32.9 K 75 K 145 K
Celsius −240 °C −198 °C −128 °C
11.7[14]
Atmosphere
Surface pressure
Trace, significant spatial variability[15][16]
Composition by volume91% water vapor
4% nitrogen
3.2% carbon dioxide
1.7% methane[17]

Enceladus is the sixth-largest moon of Saturn and the 18th largest in the Solar System. It is about 500 kilometers (310 miles) in diameter,[5] about a tenth of that of Saturn's largest moon, Titan. It is covered by clean, freshly deposited snow hundreds of meters thick, making it one of the most reflective bodies of the Solar System. Consequently, its surface temperature at noon reaches only −198 °C (75.1 K; −324.4 °F), far colder than a light-absorbing body would be. Despite its small size, Enceladus has a wide variety of surface features, ranging from old, heavily cratered regions to young, tectonically deformed terrain.

Enceladus was discovered on August 28, 1789, by William Herschel,[1][18][19] but little was known about it until the two Voyager spacecraft, Voyager 1 and Voyager 2, flew by Saturn in 1980 and 1981.[20] In 2005, the spacecraft Cassini started multiple close flybys of Enceladus, revealing its surface and environment in greater detail. In particular, Cassini discovered water-rich plumes venting from the south polar region.[21] Cryovolcanoes near the south pole shoot geyser-like jets of water vapor, molecular hydrogen, other volatiles, and solid material, including sodium chloride crystals and ice particles, into space, totaling about 200 kilograms (440 pounds) per second.[16][20][22] More than 100 geysers have been identified.[23] Some of the water vapor falls back as snow, now several hundred meters thick; the rest escapes and supplies most of the material making up Saturn's E ring.[24][25] According to NASA scientists, the plumes are similar in composition to comets.[26] In 2014, NASA reported that Cassini had found evidence for a large south polar subsurface ocean of liquid water with a thickness of around 10 km (6 mi).[27][28][29] The existence of Enceladus's subsurface ocean has since been mathematically modelled and replicated.[30]

These observations of active cryoeruptions, along with the finding of escaping internal heat and very few (if any) impact craters in the south polar region, show that Enceladus is currently geologically active. Like many other satellites in the extensive systems of the giant planets, Enceladus participates in an orbital resonance. Its resonance with Dione excites its orbital eccentricity, which is damped by tidal forces, tidally heating its interior and driving the geological activity.[31]

Cassini performed chemical analysis of Enceladus's plumes, finding evidence for hydrothermal activity,[32][33] possibly driving complex chemistry.[34] Ongoing research on Cassini data suggests that Enceladus's hydrothermal environment could be habitable to some of Earth's hydrothermal vent's microorganisms, and that plume-found methane could be produced by such organisms.[35][36]


Cite error: There are <ref group=lower-alpha> tags or {{efn}} templates on this page, but the references will not show without a {{reflist|group=lower-alpha}} template or {{notelist}} template (see the help page).

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  2. ^ "Enceladus". Lexico UK English Dictionary. Oxford University Press. Archived from the original on July 31, 2020.
    "Enceladus". Merriam-Webster.com Dictionary. Merriam-Webster.
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  5. ^ a b c d e f g "Enceladus: Facts & Figures". Solar System Exploration. NASA. August 12, 2013. Archived from the original on October 16, 2013. Retrieved April 26, 2014.
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  8. ^ a b c Jacobson, Robert. A. (November 1, 2022). "The Orbits of the Main Saturnian Satellites, the Saturnian System Gravity Field, and the Orientation of Saturn's Pole". The Astronomical Journal. 164 (5): 199. Bibcode:2022AJ....164..199J. doi:10.3847/1538-3881/ac90c9. S2CID 252992162.
  9. ^ McKinnon, W. B. (2015). "Effect of Enceladus's rapid synchronous spin on interpretation of Cassini gravity". Geophysical Research Letters. 42 (7): 2137–2143. Bibcode:2015GeoRL..42.2137M. doi:10.1002/2015GL063384.
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  13. ^ Spencer, John R.; Pearl, J. C.; et al. (2006). "Cassini Encounters Enceladus: Background and the Discovery of a South Polar Hot Spot". Science. 311 (5766): 1401–5. Bibcode:2006Sci...311.1401S. doi:10.1126/science.1121661. PMID 16527965. S2CID 44788825.
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  18. ^ Herschel, W. (January 1, 1790). "Account of the Discovery of a Sixth and Seventh Satellite of the Planet Saturn; With Remarks on the Construction of Its Ring, Its Atmosphere, Its Rotation on an Axis, and Its Spheroidal Figure". Philosophical Transactions of the Royal Society of London. 80: 1–20. doi:10.1098/rstl.1790.0004. Archived from the original on April 27, 2014. Retrieved April 27, 2014.
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  20. ^ a b Lovett, Richard A. (September 4, 2012). "Secret life of Saturn's moon: Enceladus". Cosmos Magazine. Archived from the original on August 15, 2014. Retrieved August 29, 2013.
  21. ^ Chang, Kenneth (March 12, 2015). "Suddenly, It Seems, Water Is Everywhere in Solar System". The New York Times. Archived from the original on May 9, 2020. Retrieved March 13, 2015.
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  30. ^ Tjoa, J. N. K. Y.; Mueller, M.; Tak, F. F. S. van der (April 1, 2020). "The subsurface habitability of small, icy exomoons". Astronomy & Astrophysics. 636: A50. arXiv:2003.09231. Bibcode:2020A&A...636A..50T. doi:10.1051/0004-6361/201937035. ISSN 0004-6361. S2CID 214605690.
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