TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 64 (No. 2), pp. 135-148, 2012

Ion distributions in the vicinity of Mars: Signatures of heating and acceleration processes

H. Nilsson1, G. Stenberg1, Y. Futaana1, M. Holmström1, S. Barabash1, R. Lundin1, N. J. T. Edberg2, and A. Fedorov3

1Swedish Institute of Space Physics, Kiruna, Sweden
2Swedish Institute of Space Physics, Uppsala, Sweden
3Centre d'Etude Spatiale des Rayonnements, Toulouse, France

(Received February 9, 2011; Revised April 28, 2011; Accepted April 28, 2011; Online published March 8, 2012)

Abstract: More than three years of data from the ASPERA-3 instrument on-board Mars Express has been used to compile average distribution functions of ions in and around the Mars induced magnetosphere. We present samples of average distribution functions, as well as average flux patterns based on the average distribution functions, all suitable for detailed comparison with models of the near-Mars space environment. The average heavy ion distributions close to the planet form thermal populations with a temperature of 3 to 10 eV. The distribution functions in the tail consist of two populations, one cold which is an extension of the low altitude population, and one accelerated population of ionospheric origin ions. All significant fluxes of heavy ions in the tail are tailward. The heavy ions in the magnetosheath form a plume with the flow aligned with the bow shock, and a more radial flow direction than the solar wind origin flow. Summarizing the escape processes, ionospheric ions are heated close to the planet, presumably through wave-particle interaction. These heated populations are accelerated in the tailward direction in a restricted region. Another significant escape path is through the magnetosheath. A part of the ionospheric population is likely accelerated in the radial direction, out into the magnetosheath, although pick up of an oxygen exosphere may also be a viable source for this escape. Increased energy input from the solar wind during CIR events appear to mainly increase the number flux of escaping particles, the average energy of the escaping particles is not strongly affected. Heavy ions on the dayside may precipitate and cause sputtering of the atmosphere, though fluxes are likely lower than 0.4 × 1023 s-1.
Key words: Mars, solar wind interaction, ion escape.

Corresponding author E-mail: hans.nilsson@irf.se

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