Photon Stimulated Desorption of MgS as a Potential Source of Sulfur in Mercury’s Exosphere

1,2Micah J. Schaible,3Menelaos Sarantos,4Brendan A. Anzures,4Stephen W. Parman,1,2,5Thomas M. Orlando
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2020JE006479]
1School of Chemistry and Biochemistry, Georgia Institute of Technology
2Center for Space Technology and Research, Georgia Institute of Technology
3Heliophysics Science Division, NASA Goddard Space Flight Center
4Department of Earth, Environmental and Planetary Sciences, Brown University
5School of Physics, Georgia Institute of Technology
Published by arrangement with John Wiley & Sons

Mercury has a relatively high sulfur content on its surface, and a signal consistent with ionized atomic sulfur (S+) was observed by the fast ion plasma spectrometer (FIPS) instrument on the MESSENGER spacecraft. To help confirm this assignment and to better constrain the sources of exospheric sulfur at Mercury, 193 nm photon stimulated desorption (PSD) of neutral sulfur atoms (S0) from MgS substrates was studied using resonance enhanced multiphoton ionization (REMPI) and time‐of‐flight (TOF) mass spectrometry. Though the PSD process is inherently non‐thermal, the measured velocities of ejected S0 were fit using flux weighted Maxwellian distributions with translation energies ˂E> expressed as translational “temperatures” = ˂E>/μkB. A bi‐modal distribution consisting of both thermal (= 300 ) and supra‐thermal (>1000 ) components in roughly a 2:1 ratio was found to best fit the data. The PSD cross‐section was measured to be approximately 4×10‐22 cm and, together with the velocity distributions, was used to calculate the PSD source rate of S0 into the exosphere of Mercury. Exosphere simulations using the calculated rates demonstrate that PSD is likely the primary source of S0 in Mercury’s exosphere at low (<1000 km ) altitudes.

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