Ocean planet

Illustration of a hypothetical ocean planet with a terrestrial atmosphere and two satellites

An ocean planet (also termed a waterworld) is a hypothetical type of planet whose surface is completely covered with an ocean of water.

Planetary objects that form in the outer solar system begin as a comet-like mixture of roughly half water and half rock by mass. Simulations of solar system formation have shown that planets are likely to migrate inward or outward as they form, presenting the possibility that icy planets could move to orbits where their ice melts into liquid form, turning them into ocean planets. This possibility was first discussed in the professional astronomical literature by Marc Kuchner[1] and Alain Léger[2] in 2003. Such planets could therefore theoretically support life which would be aquatic.

The oceans on such planets would be hundreds of kilometers deep, much deeper than the oceans of Earth. The immense pressures in the lower regions of these oceans could lead to the formation of a mantle of exotic forms of ice. This ice would not necessarily be as cold as conventional ice. If the planet is close enough to its sun that the water's temperature reaches the boiling point, the water will become supercritical and lack a well-defined surface.[2] Even on cooler water-dominated planets, the atmosphere can be much thicker than that of Earth, and composed largely of water vapor, producing a very strong greenhouse effect.

The extrasolar planet GJ 1214 b is the most likely known candidate for an ocean planet.[3][4] Many more such objects are expected to be discovered by the ongoing Kepler spacecraft mission.

Smaller ocean planets would have less dense atmospheres and lower gravity; thus, liquid could evaporate much more easily than on more massive ocean planets. Theoretically, such planets could have higher waves than their more massive counterparts due to their lower gravity.

Contents

Other types of ocean

Oceans, seas, lakes, etc., can be composed of liquids other than water: e.g. the hydrocarbon lakes on Titan. The possibility of seas of nitrogen on Triton was also considered but ruled out.[5] Underneath the thick atmospheres of Uranus and Neptune it is expected that these planets are composed of oceans of hot high-density fluid mixtures of water, ammonia and other volatiles.[6] The gaseous outer layers of Jupiter and Saturn transition smoothly into oceans of liquid hydrogen.[7][8] There is evidence that the icy surfaces of the moons Ganymede, Callisto, Europa, Titan and Enceladus are shells floating on oceans of very dense liquid water or water-ammonia.[9][10][11][12][13] Our own planet Earth is often called the ocean planet since it is 70% covered in water.[14][15] The atmosphere of Venus is 96.5% carbon dioxide and at the surface the pressure makes the CO2 a supercritical fluid. Extrasolar terrestrial planets that are extremely close to their parent star will be tidally-locked and so one half of the planet will be a magma ocean.[16] It is also possible that terrestrial planets had magma oceans at some point during their formation as a result of giant impacts.[17] Where there are suitable temperatures and pressures, volatile chemicals which might exist as liquids in abundant quantities on planets include: Ammonia, Argon, Carbon disulfide, Ethane, Hydrazine, Hydrogen, Hydrogen cyanide, Hydrogen sulfide, Methane, Neon, Nitrogen, Nitric oxide, Phosphine, Silane, Sulfuric acid, and Water.[18] Hot Neptunes close to their star could lose their atmospheres via hydrodynamic escape, leaving behind their cores with various liquids on the surface.[19]

Terrestrial planets will acquire water during their accretion, some of which will be buried in the magma ocean but most of it will go into a steam atmosphere, and when the atmosphere cools it will collapse on to the surface forming an ocean, and there will also be outgassing of water from the mantle as the magma solidifies - this will happen even for planets with a low percentage of their mass composed of water so "super-Earth exoplanets may be expected to commonly produce water oceans within tens to hundreds of millions of years of their last major accretionary impact."[20]

Fictional ocean planets

Fictional ocean planets have been used as story motifs, usually with clement surface temperatures and shallow oceans - unlike the very deep oceans expected on real extrasolar planets.

References

  1. ^ Kuchner, Marc (2003). "Volatile-rich Earth-Mass Planets in the Habitable Zone". Astrophysical Journal 596: L105–L108. arXiv:astro-ph/0303186. Bibcode 2003ApJ...596L.105K. doi:10.1086/378397 .
  2. ^ a b Léger, Alain (2004). "A New Family of Planets ? "Ocean Planets"". Icarus 169 (2): 499–504. arXiv:astro-ph/0308324. Bibcode 2004Icar..169..499L. doi:10.1016/j.icarus.2004.01.001 .
  3. ^ Charbonneau, David; Zachory K. Berta, Jonathan Irwin, Christopher J. Burke, Philip Nutzman, Lars A. Buchhave, Christophe Lovis, Xavier Bonfils, David W. Latham, Stéphane Udry, Ruth A. Murray-Clay, Matthew J. Holman, Emilio E. Falco, Joshua N. Winn, Didier Queloz, Francesco Pepe, Michel Mayor, Xavier Delfosse, Thierry Forveille (2009). "A super-Earth transiting a nearby low-mass star". Nature 462 (17 December 2009): 891–894. Bibcode 2009Natur.462..891C. doi:10.1038/nature08679. PMID 20016595. http://www.nature.com/nature/journal/v462/n7275/full/nature08679.html. Retrieved 2009-12-15. 
  4. ^ Kuchner, Seager; M., Hier-Majumder, C. A., Militzer (2007). "Mass–radius relationships for solid exoplanets". The Astrophysical Journal 669 (2): 1279–1297. Bibcode 2007ApJ...669.1279S. doi:10.1086/521346. http://www.iop.org/EJ/abstract/0004-637X/669/2/1279/. 
  5. ^ Page 485, Encyclopedia of the solar system By Lucy-Ann Adams McFadden, Paul Robert Weissman, Torrence V. Johnson
  6. ^ Atreya, S.; Egeler, P.; Baines, K. (2006). "Water-ammonia ionic ocean on Uranus and Neptune?". Geophysical Research Abstracts 8: 05179. Bibcode 2005AGUFM.P11A0088A. http://www.cosis.net/abstracts/EGU06/05179/EGU06-J-05179-1.pdf .
  7. ^ Guillot, T. (1999). "A comparison of the interiors of Jupiter and Saturn". Planetary and Space Science 47 (10–11): 1183–200. arXiv:astro-ph/9907402. Bibcode 1999P&SS...47.1183G. doi:10.1016/S0032-0633(99)00043-4. 
  8. ^ Lang, Kenneth R. (2003). "Jupiter: a giant primitive planet". NASA. http://ase.tufts.edu/cosmos/view_chapter.asp?id=9&page=3. Retrieved 2007-01-10. 
  9. ^ Coustenis, A.; Lunine, J.; Lebreton, J.; Matson, D.; Erd, C.; Reh, K.; Beauchamp, P.; Lorenz, R. et al. (2008). The Titan Saturn System Mission. "American Geophysical Union, Fall Meeting 2008, abstract #P21A-1346". American Geophysical Union 21: 1346. Bibcode 2008AGUFM.P21A1346C. "the Titan system, rich in organics, containing a vast subsurface ocean of liquid water" .
  10. ^ Nimmo, F; Bills, B. G. (2010). "Shell thickness variations and the long-wavelength topography of Titan". Icarus 208 (2): 896–904. Bibcode 2010Icar..208..896N. doi:10.1016/j.icarus.2010.02.020. "observations can be explained if Titan has a floating, isostatically-compensated ice shell" .
  11. ^ Goldreich, Peter M.; Mitchell, Jonathan L. (2010). "Elastic ice shells of synchronous moons: Implications for cracks on Europa and non-synchronous rotation of Titan". Icarus 209 (2): 631–638. arXiv:0910.0032. Bibcode 2010Icar..209..631G. doi:10.1016/j.icarus.2010.04.013. "A number of synchronous moons are thought to harbor water oceans beneath their outer ice shells. A subsurface ocean frictionally decouples the shell from the interior" .
  12. ^ "Study of the ice shells and possible subsurface oceans of the Galilean satellites using laser altimeters on board the Europa and Ganymede orbiters JEO and JGO" (PDF). http://meetingorganizer.copernicus.org/EPSC2009/EPSC2009-213.pdf. Retrieved 2011-10-14. 
  13. ^ "Tidal heating and the long-term stability of a subsurface ocean on Enceladus" (PDF). http://www.pmc.ucsc.edu/~jhr/research/Roberts_Nimmo_2008_Icarus.pdf. Retrieved 2011-10-14. 
  14. ^ USA (2011-10-03). "The ocean planet". Ncbi.nlm.nih.gov. http://www.ncbi.nlm.nih.gov/pubmed/12349465. Retrieved 2011-10-14. 
  15. ^ Irrigating Crops with Seawater; August 1998; Scientific American
  16. ^ Schaefer, Laura; Fegley, Bruce, Jr. (2009). "Chemistry of Silicate Atmospheres of Evaporating Super-Earths". The Astrophysical Journal Letters 703 (2): L113–L117. arXiv:0906.1204. Bibcode 2009ApJ...703L.113S. doi:10.1088/0004-637X/703/2/L113 .
  17. ^ Fluid Dynamics of a Terrestrial Magma Ocean, V. S. Solomatov, 2000
  18. ^ Tables 3 and 4 in Many Chemistries Could Be Used to Build Living Systems, WILLIAM BAINS, ASTROBIOLOGY, Volume 4, Number 2, 2004
  19. ^ Atmospheric Loss of Sub-Neptune’s and Implications for Liquid Phases of Different Solvents on Their Surfaces, J.J. Leitner (1), H. Lammer (2), P. Odert (3), M. Leitzinger (3), M.G. Firneis (1) and A. Hanslmeier (3), EPSC Abstracts, Vol. 4, EPSC2009-542, 2009, European Planetary Science Congress
  20. ^ Elkins-Tanton (2010). "Formation of Early Water Oceans on Rocky Planets". Astrophysics and Space Science 332 (2): 359–364. arXiv:1011.2710. doi:10.1007/s10509-010-0535-3. 
  21. ^ Adam Charles Roberts (2006). Science Fiction. Taylor & Francis. ISBN 9780415366687. http://books.google.com/?id=RAvM9els2acC&pg=PA17&dq=solaris+%22ocean+planet%22&cd=11#v=onepage&q=solaris%20%22ocean%20planet%22. 
  22. ^ a b "www.daviddarling.info Ocean Planet". Daviddarling.info. 2007-02-01. http://www.daviddarling.info/encyclopedia/O/ocean_planet.html. Retrieved 2011-10-14. 

External links

  • Selsis, F.; B. Chazelas, P. Borde, M. Ollivier, F. Brachet, M. Decaudin, F. Bouchy, D. Ehrenreich, J.-M. Griessmeier, H. Lammer, C. Sotin, O. Grasset, C. Moutou, P. Barge, M. Deleuil, D. Mawet, D. Despois, J. F. Kasting, A. Leger (2007). "Could we identify hot Ocean-Planets with CoRoT, Kepler and Doppler velocimetry?". Icarus 191 (2): 453. arXiv:astro-ph/0701608. Bibcode 2007Icar..191..453S. doi:10.1016/j.icarus.2007.04.010. 

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