The Lifecycle of Hollows on Mercury: An Evaluation of Candidate Volatile Phases and a Novel Model of Formation. 1 1 2 3 M. S. Phillips , J. E. Moersch , C. E. Viviano , J. P. Emery 1Department of Earth and Planetary Sciences, University of Tennessee, Knoxville 2Planetary Exploration Group, Johns Hopkins University Applied Physics Laboratory 3Department of Astronomy and Planetary Sciences, Northern Arizona University Corresponding author: Michael Phillips (
[email protected]) Keywords: Mercury, hollows, thermal model, fumarole. Abstract On Mercury, high-reflectance, flat-floored depressions called hollows are observed nearly globally within low-reflectance material, one of Mercury’s major color units. Hollows are thought to be young, or even currently active, features that form via sublimation, or a “sublimation-like” process. The apparent abundance of sulfides within LRM combined with spectral detections of sulfides associated with hollows suggests that sulfides may be the phase responsible for hollow formation. Despite the association of sulfides with hollows, it is still not clear whether sulfides are the hollow-forming phase. To better understand which phase(s) might be responsible for hollow formation, we calculated sublimation rates for 57 candidate hollow-forming volatile phases from the surface of Mercury and as a function of depth beneath regolith lag deposits of various thicknesses. We found that stearic acid (C18H36O2), fullerenes (C60, C70), and elemental sulfur (S) have the appropriate thermophysical properties to explain hollow formation. Stearic acid and fullerenes are implausible hollow-forming phases because they are unlikely to have been delivered to or generated on Mercury in high enough volume to account for hollows.