Impact-driven planetary desiccation: The origin of the dry Venus

摘要: Abstract The fate of surface water on Venus is one the most important outstanding problems in comparative planetology. Although should have had a large amount (like Earth) during its formation, current content Venusian only 1 part 100 000 that mass Earth's oceans. Here new concept proposed to explain removal steam-covered proto Venus, referred as “impact-driven planetary desiccation”. Since steam atmosphere photochemically unstable, vapor dissociates into hydrogen and oxygen. Then, escapes easily space through hydrodynamic escape driven by strong extreme ultraviolet radiation from young Sun. focus intense impact bombardment terminal stage accretion generators significant reducing agent. fine-grained ejecta remove residual oxygen, counter escaped hydrogen, via oxidation iron-bearing rocks hot atmosphere. Thus, hypervelocity impacts cause net desiccation surface. I constructed stochastic cratering model using Monte Carlo approach investigate cumulative nonoxidized, ejected due bombardment. after each was calculated π-group scaling laws modified Maxwell's Z model. effect projectile penetration ground also included. Next, an upper limit total removed stoichiometric basaltic rocks, taking account fast H2 escape. It shown thick with equivalent terrestrial oceans would be removed. rocky released reaches wt% host planet, which 10 000 times These results strongly suggest chemical reactions between such amounts atmospheres are among key factors required understand atmospheric composition, not Solar System but extrasolar systems.