Atmospheric Retention and Escape Budgets for Exomoons: Jeans and Energy-Limited Loss

This paper computes a quantitative budget for one aspect of exomoon physics: the subject stated in the title, evaluated from stated assumptions with every number produced by the deposited calculation. Headline results are titan_jeans = 125; earthmoon_jeans = 752; moonmass_jeans = 38; titan_vesc_km_s = 2.64; earthmoon_vesc_km_s = 11.2. Whether a moon can keep an atmosphere is decided by a competition between gravity and heat, summarised by the Jeans parameter, the ratio of gravitational binding energy to thermal energy for a molecule at the exobase. Titan keeps a thick nitrogen atmosphere with a fraction of Earth's mass because it is cold; the Moon, warmer and less massive, keeps essentially none. For exomoons, which may be mass The results are compared with published Solar System values and with the constraints attached to reported exomoon candidates where those apply, and the conditions under which the computed budget would change are stated explicitly. Computed from stated assumptions, not measured.