Habitable Moons Around Extrasolar Giant Planets

Details Habitable Moons Around Extrasolar Giant Planets Habitable Moons Around Extrasolar Giant Planets

Sep 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.1221w&link_type=abstract

American Astronomical Society, DPS meeting #28, #12.21; Bulletin of the American Astronomical Society, Vol. 28, p.1115

Astronomy and Astrophysics

Astronomy

1

Scientific paper

Jovian-sized planets have recently been discovered around eight different main-sequence stars. Giant, gaseous planets are unlikely to harbor terrestrial-type life, but their moons might conceivably be habitable if they lie within the terrestrial planet habitable zone (HZ). Although none of the new extrasolar planets is within the HZ, their distribution around the HZ suggests that an extrasolar giant planet, with potentially habitable moons, might soon be found within its limits. A habitable moon must first form and then be able to retain an atmosphere. Impact-generated atmospheres are most likely to form on large moons, born far from their parent stars (e.g., Titan) where the relative velocities of infalling comets are small. A moon's ability to retain a N_2 atmosphere depends primarily on its mass, the flux of ionizing radiation it receives from its star, and the charged particle flux it receives within the magnetosphere of its planet. Nitrogen loss due to sputtering would be most important for non-magnetic moons. Moons <0.12M_⊕ would lose most of their nitrogen over 4.5 Gyr via nonthermal, dissociative recombination of N_2(+) . Additional factors which might affect habitability are synchronous rotation and depth of oceans. Moons formed initially of ice (e.g., Ganymede) would have 1000km-deep oceans within the HZ. Rocky moons (e.g., Io, or Europa) with smaller endowments of water would have a better chance of supporting land-based life on dry continents. Finally, a moon must be able to compensate for the gradual brightening of its star to remain habitable for billions of years. Long-lived, temperate climates are stabilized by the carbonate-silicate weathering cycle, which controls levels of CO_2 and, hence, greenhouse warming through chemical weathering and plate tectonics. Tectonic activity may be sustained by radiogenic heating for 4.5 Gyr on moons >0.23M_⊕. Smaller moons might also exhibit long-lived plate tectonics if they are heated tidally through resonance interactions with adjacent moons, as is Io.

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