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First ENA observations at Mars: Subsolar ENA jet |
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| Authors: | Y Futaana S Barabash M Holmström E Kallio H Gunell R Lundin M Yamauchi JD Winningham JR Sharber AJ Coates DO Kataria P Riihelä H Koskinen J Luhmann D Williams CC Curtis BR Sandel M Carter A Fedorov S Orsini M Maggi P Bochsler J Woch K Asamura |
| Institution: | a Swedish Institute of Space Physics, Box 812, SE-981 28 Kiruna, Sweden b NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA c Finnish Meteorological Institute, Box 503, FIN-00101 Helsinki, Finland d Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723-6099, USA e Space Technology Ireland, National University of Ireland, Maynooth, Co. Kildare, Ireland f Southwest Research Institute, San Antonio, TX 7228-0510, USA g Mullard Space Science Laboratory, University College London, Surrey RH5 6NT, UK h Department of Physical Sciences, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland i Space Physics Research Laboratory, University of Michigan, Ann Arbor, MI 48109-2143, USA j Space Science Laboratory, University of California in Berkeley, Berkeley, CA 94720-7450, USA k University of Arizona, Tucson, AZ 85721, USA l Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK m Centre d'Etude Spatiale des Rayonnements, BP-4346, F-31028 Toulouse, France n Istituto di Fisica dello Spazio Interplanetari, I-00133 Rome, Italy o Physikalisches Institut, University of Bern, CH-3012 Bern, Switzerland p Max-Planck-Institut für Aeronomie, D-37191 Katlenburg-Lindau, Germany q Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Japan r Technical University of Braunschweig, Hans-Sommer-Strasse 66, D-38106 Braunschweig, Germany |
| Abstract: | The Neutral Particle Detector (NPD), an Energetic Neutral Atom (ENA) sensor of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) on board Mars Express, detected intense fluxes of ENAs emitted from the subsolar region of Mars. The typical ENA fluxes are (4-7) × 105 cm−2 sr−1 s−1 in the energy range 0.3-3 keV. These ENAs are likely to be generated in the subsolar region of the martian exosphere. As the satellite moved away from Mars, the ENA flux decreased while the field of view of the NPD pointed toward the subsolar region. These decreases occurred very quickly with a time scale of a few tens of seconds in two thirds of the orbits. Such a behavior can be explained by the spacecraft crossing a spatially constrained ENA jet, i.e., a highly directional ENA emission from a compact region of the subsolar exosphere. This ENA jet is highly possible to be emitted conically from the subsolar region. Such directional ENAs can result from the anisotropic solar wind flow around the subsolar region, but this can not be explained in the frame of MHD models. |
| Keywords: | Mars atmosphere Solar wind Magnetospheres |
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