Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low‐Mass Dwarf Stars. II. Sulfur and Phosphorus

Thermochemical equilibrium and kinetic calculations are used to model sulfurand phosphorus chemistry in giant planets, brown dwarfs, and extrasolar giantplanets (EGPs). The chemical behavior of individual S- and P-bearing gases andcondensates is determined as a function of pressure, temperature, andmetallicity. The results are independent of particular model atmospheres and,in principle, the equilibrium composition along the pressure-temperatureprofile of any object can be determined. Hydrogen sulfide (H2S) is the dominantS-bearing gas throughout substellar atmospheres and approximately representsthe atmospheric sulfur inventory. Silicon sulfide (SiS) is a potential tracerof weather in substellar atmospheres. Disequilibrium abundances of phosphine(PH3) approximately representative of the total atmospheric phosphorusinventory are expected to be mixed upward into the observable atmospheres ofgiant planets and T dwarfs. In hotter objects, several P-bearing gases (e.g.,P2, PH3, PH2, PH, HCP) become increasingly important at high temperatures.Comment: 38 pages, 8 figures, accepted for Astrophysical Journa