We found a match
Your institution may have rights to this item. Sign in to continue.
- Title
Photon‐Stimulated Desorption of MgS as a Potential Source of Sulfur in Mercury's Exosphere.
- Authors
Schaible, Micah J.; Sarantos, Menelaos; Anzures, Brendan A.; Parman, Stephen W.; Orlando, Thomas M.
- Abstract
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) spectroscopy and time‐of‐flight (TOF) mass spectrometry. Though the PSD process is inherently nonthermal, the measured velocities of ejected S0 were fit using flux‐weighted Maxwellian distributions with translation energies <E> expressed as translational "temperatures" Ttrans = <E>/μkB. A bimodal distribution consisting of both thermal (Ttrans = 300 K) and suprathermal (Ttrans > 1,000 K) 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 cm2 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 (<1,000 km) altitudes. Plain Language Summary: Mercury has a relatively high sulfur content on its surface, and the Fast Ion Plasma Spectrometer (FIPS) instrument on the MESSENGER spacecraft observed a signal consistent with elemental sulfur ions in the extremely tenuous atmosphere above the surface, the exosphere. However, current estimates of sulfur desorption from Mercury's surface based on solar wind sputtering and micrometeorite impact vaporization underestimate the observed abundances. Solar photons can also eject volatile species through a process known as photon‐stimulated desorption (PSD) where photons with enough energy can excite repulsive electronic states in surface atoms, leading to desorption. By irradiating magnesium sulfide (MgS) samples with ultraviolet photons simulating solar photon radiation, this work provides the first PSD measurements of neutral sulfur atoms from material that could be present on the surface of Mercury. Our results show that PSD can eject significant amounts of sulfur from Mercury's surface and should be included in future exosphere modeling efforts. Key Points: Sulfur is an expected component of Mercury's exosphere, but observed sulfur ion abundances are underestimated by current exosphere formation modelsThe velocity distribution and cross‐section for photon‐stimulated desorption (PSD) of neutral sulfur was measured from MgS using REMPI‐TOFEstimates of the desorption rate produced by solar photons suggest that PSD should be included as a source of exospheric sulfur at Mercury
- Subjects
MULTIPHOTON ionization; MASS spectrometry; HOMOGENEITY; SEISMOMETERS; MICROWAVES
- Publication
Journal of Geophysical Research. Planets, 2020, Vol 125, Issue 8, p1
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2020JE006479