Summary:

H2S is a major volatile sulfur carrier, and is thought to be present in interstellar ices in significant amounts (~1% w.r.t. H2O). Understanding the desorption behavior of H2S is crucial for interpreting the sulfur chemical network in star and planet forming regions, and predicting in what physical state it may be incorporated by forming planets and planetesimals. For the first time, we experimentally characterize the sublimation dynamics of H2S ice and derive its corresponding desorption temperatures and snowline positions in a representative T-Tauri disk midplane. We determine binding energies in the multilayer regime, where H2S primarily interacts with other H2S molecules, as well as in the submonolayer regime on top of a compact amorphous solid water substrate, that is, where H2S interacts primarily with H2O. Both cases lead to sublimation fronts located just interior to the CO2 snowline. However, we find that the entrapment of H2S in water ice is highly efficient (≳ 75%), effectively shifting its snowline position closer to the H2O snowline, assuming it forms mixed with water. Therefore, H2S is expected to remain in the solid phase throughout the entire region where comets and icy asteroids form.

View paper