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Habitability of Large Exomoons

22 Nov 2013, 10:06 UTC
Habitability of Large Exomoons
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Large exomoons around giant planets in the habitable zone of their host stars could serve as habitats for extraterrestrial life. Such an exomoon would need to have at least twice the mass of Mars or so (i.e. ~0.2 Earth masses) for it to be habitable. For comparison, Ganymede, the largest moon in the Solar System, is roughly 1/40 the mass of Earth. In addition, habitability requires a surface temperature that cannot be too high or too low. This is governed not just by stellar radiation from the host star, but also by stellar light reflected from the giant planet, thermal radiation from the giant planet itself and tidal heating.Figure 1: Artist’s impression of a giant planet hosting a system of moons. Credit: Kevin Sherman.Over time, a gaseous giant planet contracts and releases thermal energy as it converts gravitational potential energy into heat. In a paper by Heller & Barnes (2013), the authors investigate how thermal radiation from a shrinking gaseous giant planet could drive a runaway greenhouse effect for an Earth-like exomoon if it is in a close enough orbit around the giant planet. This effect is particularly significant for a young giant planet during the first few hundred million ...

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