The contribution of impulsive meteoritic impact vapourization to the Hermean exosphere |
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| Institution: | 1. INAF-IFSI, via Fosso del Cavaliere 100, 00133 Roma, Italy;2. CISAS-“G.Colombo”, via Via Venezia 15, 35131 Padova, Italy;3. AMDL srl, Roma, Italy;4. Physics Institute, University of Bern, Sidlerstrasse. 5, CH-3012 Bern, Switzerland;1. INAF Osservatorio Astronomico Padova, Padova, Italy;2. Service d'' Aéronomie, Université de Paris Pierre et Marie Curie, Paris, France;1. Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, USA;2. Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, Boulder, CO 80309, USA;3. Scripps Institution of Oceanography (SIO), University of California, San Diego, La Jolla, CA 92093, USA;4. Australian Nuclear Science and Technology Organisation (ANSTO), Locked Bag 2001, Kirrawee DC, NSW 2232, Australia;5. National Institute of Water and Atmospheric Research Ltd. (NIWA), P.O. Box 14901, Kilbirnie, 301 Evans Bay Parade, Wellington, New Zealand;6. Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, DK-2100-Copenhagen, Denmark;1. Institute of Astronomy, National Central University, Taiwan;2. Institute of Space Science, National Central University, Taiwan;3. Space Science Institute, Macau University of Science and Technology, Macau;4. Space Science Laboratory, University of California, Berkeley, USA;1. Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA;2. Goddard Earth Sciences, Technology, and Research, Morgan State University, Baltimore, MD 21251, USA;3. Goddard Planetary Heliophysics Institute, University of Maryland Baltimore County, Baltimore, MD 21250, USA;4. Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA;5. Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA;6. The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA;1. Laboratory for Space Sciences and Physics Department, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130-4899, USA;2. Department of Earth and Planetary Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130-4899, USA;3. McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130-4899, USA;4. Lunar and Planetary Laboratory, The University of Arizona, 1629 E. University Blvd., Kuiper, Space Science Bldg, Tucson, AZ 85721-0092, USA;5. Department of Material Science and Engineering, The University of Arizona, 1235 E. James E. Rogers Way, Tucson, AZ 85721-0012, USA |
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| Abstract: | The exosphere of Mercury has been the object of many investigations and speculations regarding its composition, formation, depletion and dynamics. While vapourization of Mercurian surface materials by meteorite impacts has been often considered to be a less important contributor to the exosphere than other potential processes, larger objects coming from the Main Asteroid Belt could cause high local and transient enhancements in the density of the exosphere. Vapourization by such impacts is an almost stoichiometric process, and thus would contain valuable information about the surface composition. We investigate some exospheric effects of impact vapourization for meteorites with radii of 1, 10 cm, and 1 m, with particular reference to the missions that will explore Mercury during the next decade (MESSENGER and BepiColombo). Because of their higher probabilities, impacts of objects in the two smaller size ranges will surely occur during the lifetimes of the two missions. The enhancement of the exospheric density on the dayside of Mercury would be appreciable for the 10-cm and 1-m meteorites (some orders of magnitude, especially for Al, Mg, Si, and Ca). Such events could allow detection, for the first time, of refractory species like Al, Mg, and Si, which are expected to exist on the surface but have not yet been detected in the exosphere. Ca could be detectable in all cases, even if produced by impacting objects as small as 1 cm in radius. The lower exospheric background on the night side should allow easier identification of Na and K produced by impulsive events, even if their generally high background values make this eventuality less likely. |
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