Hydrothermal processing of cometary volatiles--applications to Triton.

Subsequent to its capture by Neptune, Triton could have experienced an episode of tidal heating sufficient to melt its icy mantle and possibly its rocky core as well. This heating would have driven hydrothermal circulation at the core-rock/mantle-ocean boundary. We consider the chemical consequences of this hydrothermal reprocessing on Triton's volatile budget by assuming an initial cometary composition for the icy mantle and evaluating the effects of changes in temperature and oxidation state. We assume that the latter would have been controlled by mineral assemblages in the rock. Such reprocessing could explain the lack of carbon monoxide in the atmosphere of Triton and its depletion relative to N2 and (apparently) CO2 in the satellite's surface ices. Our calculations also show that whatever the original source of nitrogen in Triton, N2 and/or NH3 are likely abundant products of hydrothermal reprocessing. Depending on the temperature and prevailing oxidation state, acetic acid, ethanol, urea, methanol, and ethanamine are possible important components, in addition to ammonia, of the resulting mantle material. Triton may thus preserve the organic chemistry that might have led to the origin of life in early terrestrial hydrothermal systems.