Ocean planet

Artist's illustrations of hypothetical ocean planets with two natural satellites.

An ocean planet, aquaplanet or water world^[1] is a hypothetical type of exoplanet that has a substantial fraction of its mass made of water. The surface on such planets would be completely covered with an ocean of water hundreds of kilometers deep, much deeper than the oceans of Earth.

Formation

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^[2] and Alain Léger^[3] in 2003.

Structure

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 star that the water reaches its boiling point, the water will become supercritical and lack a well-defined surface.^[3] 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.

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.

Examples

The extrasolar planet GJ 1214 b is the most likely known candidate for an ocean planet.^[4][5] Many more such objects are expected to be discovered by Kepler, such as the recently discovered ocean planet candidate Kepler-22b.

Terraforming

An ocean planet has no dry surface landmasses. One of two processes would be required:

1. Constructing an artificial surface.
2. Draining away some of the water to expose land

See also

• Chthonian planet (theoret.)
• Desert planet
• Earth analog
• Eccentric Jupiter
• Hot Jupiter
• Hot Neptune
• Ice planet
• Ocean § Extraterrestrial oceans
• Planets in science fiction § Ocean planets
• Pulsar planet
• Rogue planet
• Super-Earth
• Transiting planet
• Trojan planet (theoret.)

References

1. "Water Worlds and Ocean Planets". Solsation.com. 2013. Retrieved January 7, 2016.
2. 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.
3. 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.
4. David Charbonneau; Zachory K. Berta; Jonathan Irwin; Christopher J. Burke; et al. (2009). "A super-Earth transiting a nearby low-mass star". Nature 462 (17 December 2009): 891–894. arXiv:0912.3229. Bibcode:2009Natur.462..891C. doi:10.1038/nature08679. PMID 20016595. Retrieved 2009-12-15.
5. Kuchner, Seager; Hier-Majumder, M.; Militzer, C. A. (2007). "Mass–radius relationships for solid exoplanets". The Astrophysical Journal 669 (2): 1279–1297. arXiv:0707.2895. Bibcode:2007ApJ...669.1279S. doi:10.1086/521346.

External links

• F. Selsis; B. Chazelas; P. Borde; M. Ollivier; et al. (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.