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First ENA observations at Mars: Solar-wind ENAs on the nightside |
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| Authors: | K Brinkfeldt H Gunell P C:son Brandt RA Frahm E Kallio Y Futaana R Lundin M Yamauchi JR Sharber AJ Coates DO Kataria T Säles W Schmidt J Luhmann D Williams CC Curtis BR Sandel M Carter A Fedorov S McKenna-Lawler R Cerulli-Irelli P Wurz N Krupp M Fränz C Dierker |
| Institution: | a Swedish Institute of Space Physics, Box 812, S-98 128 Kiruna, Sweden b Space Technology Ltd., National University of Ireland, Maynooth, Co. Kildare, Ireland c Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723-6099, USA d Southwest Research Institute, San Antonio, TX 7228-0510, USA e Finnish Meteorological Institute, Box 503, FIN-00101 Helsinki, Finland f Mullard Space Science Laboratory, University College London, Surrey RH5 6NT, UK g Space Physics Research Laboratory, University of Michigan, Ann Arbor, MI 48109-2143, USA h Space Science Laboratory, University of California in Berkeley, Berkeley, CA 94720-7450, USA i University of Arizona, Tucson, AZ 85721, USA j Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK k Centre d'Etude Spatiale des Rayonnements, BP-4346, F-31028 Toulouse, France l Istituto di Fisica dello Spazio Interplanetari, I-00133 Rome, Italy m Physikalisches Institut, University of Bern, CH-3012 Bern, Switzerland n Max-Planck-Institut für Aeronomie, D-37191 Katlenburg-Lindau, Germany o Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamichara, Japan p Technical University of Braunschweig, Hans-Sommer-Strasse 66, D-38106 Braunschweig, Germany |
| Abstract: | We present measurements with an Energetic Neutral Atom (ENA) imager on board Mars Express when the spacecraft moves into Mars eclipse. Solar wind ions charge exchange with the extended Mars exosphere to produce ENAs that can spread into the eclipse of Mars due to the ions' thermal spread. Our measurements show a lingering signal from the Sun direction for several minutes as the spacecraft moves into the eclipse. However, our ENA imager is also sensitive to UV photons and we compare the measurements to ENA simulations and a simplified model of UV scattering in the exosphere. Simulations and further comparisons with an electron spectrometer sensitive to photoelectrons generated when UV photons interact with the spacecraft suggest that what we are seeing in Mars' eclipse are ENAs from upstream of the bow shock produced in charge exchange with solar wind ions with a non-zero temperature. The measurements are a precursor to a new technique called ENA sounding to measure solar wind and planetary exosphere properties in the future. |
| Keywords: | Mars Solar wind Magnetospheres |
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