The role of surface volatile exchanges in evolving climate conditions on terrestrial planets

The habitability of a terrestrial planet depends on its surface conditions, which can vary greatly during its evolution. Volatile exchanges between the interior, the surface and the atmosphere - the cycles of volatile species or their absence - are largely responsible for these variations and the resulting complex feedback mechanisms between the processes involved. The differences between Earth and Venus climate conditions highlight how similar processes and base characteristics can lead to divergent states after billions of years of evolution. While Venus exhibits hostile conditions and its atmosphere appears mostly desiccated, some hypothetical evolution scenarios suggest it was not always so, and that it could have sustained liquid water oceans for an undefined period of time during its past history. We investigate what mechanisms are likely to be responsible for this type of catastrophic change on Venus and possibly on terrestrial planets, using coupled numerical evolution simulations of planetary evolution, involving mantle dynamics, volcanism, atmospheric greenhouse, escape mechanisms, meteoritic impacts and surface solid-gas exchanges. Increasing solar luminosity (the faint young sun paradox) only marginally affects surface temperature changes. Atmospheric escape could only hide the results of a runaway greenhouse phase by removing water rather than cause the observed climate change. Moreover, it is shown, especially in light of recent measurements interpretation, to be unlikely to be responsible for massive water loss. Large impacts, capable of releasing large amounts of volatiles in the atmosphere, are infrequent and unlikely to occur during late evolution. The smaller impactors do not have enough mass to affect the mantle or atmosphere substantially.  The cause of catastrophic transitions and the means to dessicate the atmosphere of Venus post-runaway greenhouse may be internal. We investigate volcanic gas release based on mantle composition and mantle dynamics over time, as well as oxidation mechanisms of fresh material that can trap volatiles into the surface. Solid surface oxidation is inefficient and appears to be roughly as efficient (within 0.1-1 order of magnitude) as recent atmospheric escape, when considering O removal during the last few billion years. Ashes oxidation could be more efficient but requires explosive volcanism that is not widespread on Venus, given the few traces detected from surface observation. We compare its effects to that on Earth. However, large variations in atmospheric composition and vertical structure resulting from runaway greenhouse could affect all the mechanisms involved in the evolution of terrestrial planets and, under some circumstances lead to a late molten surface phase. Surface exchanges and atmospheric loss would therefore be affected in turn.