Author/Authors :
Lundin، نويسنده , , R. and Winningham، نويسنده , , D. and Barabash، نويسنده , , S. and Frahm، نويسنده , , R.A. and Andersson، نويسنده , , H. and Holmstrِm، نويسنده , , M. M. Grigoriev، نويسنده , , A. and Yamauchi، نويسنده , , Holly M. Brown-Borg، نويسنده , , H. and Sharber، نويسنده , , J.R. and Sauvaud، نويسنده , , J.-A. and Fedorov، نويسنده , , A. and Budnik، نويسنده , , E. and Thocaven، نويسنده , , J.-J. and Asamura، نويسنده , , K. and Hayakawa، نويسنده , , H. and Coates، نويسنده , , A.J. and Linder، نويسنده , , D.R. and Kataria، نويسنده , , D.O. and Curtis، نويسنده , , C. and Hsieh، نويسنده , , K.C. and Sandel، نويسنده , , B.R. and Grande، نويسنده , , M. and Carter، نويسنده , , M. and Reading، نويسنده , , D.H. and Koskinen، نويسنده , , H. and Kallio، نويسنده , , E. and Riihelن، نويسنده , , P. and Schmidt، نويسنده , , W. and Sنles، نويسنده , , T. and Kozyra، نويسنده , , John J. and Krupp، نويسنده , , N. and Woch، نويسنده , , J. and Frنnz، نويسنده , , M. and Luhmann، نويسنده , , J. and McKenna-Lawler، نويسنده , , S. and Cerulli-Irelli، نويسنده , , R. and Orsini Cancelli، نويسنده , , S. and Maggi، نويسنده , , M. and Roelof، نويسنده , , E. and Williams، نويسنده , , Julie D. and Livi، نويسنده , , S. and Brandt، نويسنده , , P. C:son and Wurz، نويسنده , , P. and Bochsler، نويسنده , , P.، نويسنده ,
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 Earthʹs 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.
