^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” T _t = ˂E>/μk_B. A bi‐modal distribution consisting of both thermal (T _t = 300 K ) and supra‐thermal (T _t >1000 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 cm ² 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.

¹Sandra Pizzarello,²Christopher T. Yarnes,³George Cooper
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13532]
¹School of Molecular Sciences, Arizona State University, Tempe, Arizona, 85287‐1604 USA
²Stable Isotope Facility, University of California, One Shields Ave. MS 1, Davis, California, 95616 USA
³NASA‐Ames Research Center, Moffett Field, California, 94035 USA
Published by arrangement with John Wiley & Sons

To date, the CM2 class of carbonaceous chondrites has provided the most detailed view of organic synthesis in the early solar system. Organic‐rich chondrites actually observed falling to Earth (“Falls”), for example, the Murchison meteorite in 1969, are even more rare. The April 23, 2019 fall of the Aguas Zarcas meteorite is therefore the most significant CM2 fall since Murchison. Samples collected immediately following the fall provide the rare opportunity to analyze its bulk mineralogy and organic inventory relatively free of terrestrial contamination. According to the Meteoritical Bulletin, Aguas Zarcas (“AZ” or “Zarcas”) is dominated by serpentine, similar to other CM2 chondrites. Likewise, our initial analyses of AZ were meant to give a broad view of its soluble organic inventory relative to other carbonaceous chondrites. We observe that while it is rich in hydrocarbons, carboxylic acids, dicarboxylic acids, sugar alcohols, and sugar acids, some of these classes may be of lesser abundance than in the more well known carbonaceous chondrites such as Murchison. Compared generally with other CM2 meteorites, the most significant finding is the absence, or relatively low levels, of three otherwise common constituents: ammonia, amino, acids, and amines. Overall, this meteorite adds to the building database of prebiotic compounds available to the ancient Earth.