The Lifecycle of Hollows on Mercury: An Evaluation of Candidate Volatile Phases and a Novel Model of Formation.

A thermophysical model was developed to test the viability of 57 candidate hollow-forming volatiles within the hollow-formation model framework of Blewett et al. (2013). We find that the thermophysical properties of elemental sulfur (S) combined with the abundance of S on Mercury, make it the most likely hollow-forming volatile explored in this study. We propose a novel model for hollow formation in which a subsurface heat source drives sulfur-rich systems that deposit volatiles (importantly, S) in the near-surface at night within a "sulfur permafrost zone", and daytime solar heating drives sublimation to form hollows.