Electron transport and precipitation at Mercury during the MESSENGER flybys: Implications for electron-stimulated desorption |
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| Authors: | David Schriver Pavel Trávní?ek Maha Ashour-Abdalla Robert L Richard Petr Hellinger James A Slavin Brian J Anderson Daniel N Baker Mehdi Benna Scott A Boardsen Robert E Gold George C Ho Haje Korth Stamatios M Krimigis William E McClintock Jason L McLain Thomas M Orlando Menelaos Sarantos Ann L Sprague Richard D Starr |
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| Institution: | aInstitute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567, USA;bDepartment of Physics and Astronomy, University of California, Los Angeles, CA 90095-1567, USA;cSpace Sciences Laboratory, University of California, Berkeley, CA 94720-7450, USA;dAstronomical Institute, ASCR, 14131 Prague, Czech Republic;eHeliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA;fJohns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA;gLaboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA;hSolar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA;iAcademy of Athens, Office of Space Research Technology, Athens 11527, Greece;jSchool of Chemistry and Biochemistry and School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA;kLunar and Planetary Laboratory University of Arizona, Tucson, AZ 85721, USA;lPhysics Department, The Catholic University of America, Washington, DC 20064, USA |
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| Abstract: | To examine electron transport, energization, and precipitation in Mercury's magnetosphere, a hybrid simulation study has been carried out that follows electron trajectories within the global magnetospheric electric and magnetic field configuration of Mercury. We report analysis for two solar-wind parameter conditions corresponding to the first two MESSENGER Mercury flybys on January 14, 2008, and October 6, 2008, which occurred for similar solar wind speed and density but contrasting interplanetary magnetic field (IMF) directions. During the first flyby the IMF had a northward component, while during the second flyby the IMF was southward. Electron trajectories are traced in the fields of global hybrid simulations for the two flybys. Some solar wind electrons follow complex trajectories at or near where dayside reconnection occurs and enter the magnetosphere at these locations. The entry locations depend on the IMF orientation (north or south). As the electrons move through the entry regions they can be energized as they execute non-adiabatic (demagnetized) motion. Some electrons become magnetically trapped and drift around the planet with energies on the order of 1–10 keV. The highest energy of electrons anywhere in the magnetosphere is about 25 keV, consistent with the absence of high-energy (>35 keV) electrons observed during either MESSENGER flyby. Once within the magnetosphere, a fraction of the electrons precipitates at the planetary surface with fluxes on the order of 109 cm−2 s−1 and with energies of hundreds of eV. This finding has important implications for the viability of electron-stimulated desorption (ESD) as a mechanism for contributing to the formation of the exosphere and heavy ion cloud around Mercury. From laboratory estimates of ESD ion yields, a calculated ion production rate due to ESD at Mercury is found to be on par with ion sputtering yields. |
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| Keywords: | Mercury Magnetosphere Numerical simulations Electron transport Electron-stimulated desorption MESSENGER |
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