September 2020 Virtual Meeting

Monday, September 14, 2020
6:00 - 7:30 pm

Note: ETGS members will receive an email with info for logging into the meeting.


Brimstone Volatiles and Hermean Hollows


Michael Phillips
PhD Student
Department of Earth and Planetary Sciences
University of Tennessee Knoxville


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 volatiles phases from the surface of Mercury and as a function of depth beneath regolith lag deposits of various thicknesses. We find that stearic acid (C18H36O2), fullerenes (C60, C70), and elemental sulfur (S) have the appropriate thermophysical properties to explain hollow formation. We suggest that S is most likely the phase responsible for hollow formation based on its abundance on Mercury and its thermophysical properties. We discuss the possibility that S is the phase responsible for hollow formation within the hollow-formation model framework proposed by Belwett et al. (2013). However, several potential limitations with that model lead us to suggest an alternative hollow-formation model that involves daytime sublimation of S (and S-bearing gases) from the vicinity of fumarole systems where S and other phases accumulate at night. We call this hollow-formation model Sublimation Cycling Around Fumarole Systems, or SCArFS. We suggest that the thermal decomposition of sulfides within LRM is a main contributor to S and S-bearing gases within the proposed fumarole systems and that (re-)precipitation of sulfides may occur at the surface along hollow floors and rims.


Michael is a Dawn and Lawrence Taylor Doctoral Research Fellow pursuing his PhD at the University of Tennessee, Knoxville. He recently won a grant from the NASA Mars Data Analysis Program worth over $500,000 to study the composition of ancient martian crust. His other research interests include the surface of Mercury and remote detection of early habitats on Mars.

Greetings, and welcome to the September 14, 2020 ETGS virtual meeting. We hope you, your family, and your colleagues are staying healthy.

As a courtesy please mute your cell phone or the microphone in your laptop/tablet to minimize background noise and feedback echos. We will also make an effort to mute all participants - at least until the presentation is finished. Please use the chat feature to type any comments or questions you may have. We recommend that you send questions for the speaker to "everyone" so all participants can see the question. In the interest of time, we may hold the Q&A at the end of the presentation.

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Thank you for your patience and understanding as we try this online format. As always, we welcome and appreciate your feedback and suggestions for improvement.



Page updated September 15, 2020