|
|||||
|
|
Ionospheric plasma acceleration at Mars: ASPERA-3 results |
|
| Authors: | R Lundin D Winningham RA Frahm M Holmström M Yamauchi JR Sharber A Fedorov J-J Thocaven H Hayakawa DR Linder C Curtis BR Sandel M Carter H Koskinen P Riihelä T Säles N Krupp M Fränz S McKenna-Lawler S Orsini E Roelof S Livi P Wurz |
| Institution: | a Swedish Institute of Space Physics, Box 812, S-98 128, Kiruna, Sweden b Southwest Research Institute, San Antonio, TX 7228-0510, USA c Centre d'Etude Spatiale des Rayonnements, BP-4346, F-31028 Toulouse, France d Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamichara, Japan e Mullard Space Science Laboratory, University College London, Surrey RH5 6NT, UK f University of Arizona, Tucson, AZ 85721, USA g Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK h Finnish Meteorological Institute, Box 503, FIN-00101 Helsinki, Finland i Space Physics Research Laboratory, University of Michigan, Ann Arbor, MI 48109-2143, USA j Max-Planck-Institut für Sonnensystemforschung, D-37191 Katlenburg-Lindau, Germany k Space Science Laboratory, University of California in Berkeley, Berkeley, CA 94720-7450, USA l Space Technology Ltd., National University of Ireland, Maynooth, Co. Kildare, Ireland m Istituto di Fisica dello Spazio Interplanetari, I-00133 Rome, Italy n Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723-6099, USA o Physikalisches Institut, University of Bern, CH-3012 Bern, Switzerland |
| Abstract: | The Analyzer of Space Plasma and Energetic Atoms (ASPERA) on-board the Mars Express spacecraft (MEX) measured penetrating solar wind plasma and escaping/accelerated ionospheric plasma at very low altitudes (250 km) in the dayside subsolar region. This implies a direct exposure of the martian topside atmosphere to solar wind plasma forcing leading to energization of ionospheric plasma. The ion and electron energization and the ion outflow from Mars is surprisingly similar to that over the magnetized Earth. Narrow “monoenergetic” cold ion beams, ion beams with broad energy distributions, sharply peaked electron energy spectra, and bidirectional streaming electrons are particle features also observed near Mars. Energized martian ionospheric ions (O+, O+2, CO+2, etc.) flow in essentially the same direction as the external sheath flow. This suggests that the planetary ion energization couples directly to processes in the magnetosheath/solar wind. On the other hand, the beam-like distribution of the energized plasma implies more indirect energization processes like those near the Earth, i.e., energization in a magnetized environment by waves and/or parallel (to B) electric fields. The general conditions for martian plasma energization are, however, different from those in the Earth's magnetosphere. Mars has a weak intrinsic magnetic field and solar wind plasma may therefore penetrate deep into the dense ionospheric plasma. Local crustal magnetization, discovered by Acuña et al. Acuña, M.J., Connerey, J., Ness, N., Lin, R., Mitchell, D., Carlsson, C., McFadden, J., Anderson, K., Rème, H., Mazelle, C., Vignes, D., Wasilewski, P., Cloutier, P., 1999. Science 284, 790-793], provide some dayside shielding against the solar wind. On the other hand, multiple magnetic anomalies may also lead to “hot spots” facilitating ionospheric plasma energization. We discuss the ASPERA-3 findings of martian ionospheric ion energization and present evidences for two types of plasma energization processes responsible for the low- and mid-altitude plasma energization near Mars: magnetic field-aligned acceleration by parallel electric fields and plasma energization by low frequency waves. |
| Keywords: | Mars atmosphere Ionospheres Magnetospheres |
| 本文献已被 ScienceDirect 等数据库收录！ | |