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Beyond Earthly Skies

Capturing Terrestrial-Sized Moons

18 Aug 2013, 14:01 UTC
Capturing Terrestrial-Sized Moons
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Terrestrial-sized moons can exist around gas giant planets. This is especially interesting for gas giant planets that occupy the habitable zone around their host stars because terrestrial-sized moons around such planets can support Earth-like conditions. A terrestrial-sized moon requires a minimum mass of at least 0.1 to 0.2 Earth mass in order to hold on to an atmosphere for billions of years. This is about 4 to 5 times more massive than the largest moons in our Solar System and is comparable to the mass of Mars.The largest moons in our Solar System presumably formed through accretion of material in the circumplanetary disks around Jupiter and Saturn. This poses a problem for forming a terrestrial-sized moon because there is not enough material and/or accretion efficiency in the circumplanetary disk around Jupiter or Saturn to form anything more massive than ~ 0.025 Earth mass. The moons Callisto and Ganymede around Jupiter, and Titan around Saturn show that a formation process via accretion in a circumplanetary disk is unlikely to form a moon larger than 1/10,000th the mass of its host planet.Williams (2013) proposes that terrestrial-sized moons can exist around gas giant planets through a formation process known as binary-exchange capture. This ...

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