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

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 × 10 23 s −1 .

Proton Temperature Anisotropies in the Plasma Environment of Venus

“…The planetary ions are gradually accelerated to escape energies throughout the tail. At Mars studies have shown that a low energy tailward drifting component is dominating large parts of the tail (Nilsson et al, ). The situation in Venus's magnetotail is complicated as there is a substantial flow of ions returning toward Venus (Kollmann et al, ; Persson et al, ).…”

Mars‐solar wind interaction: LatHyS, an improved parallel 3‐D multispecies hybrid model

“…Nilsson et al [] have estimated the tailward flux escape inside the nominal Induced Magnetospheric Boundary as a function of the tail distance. The average value is 1.1 × 10 24 s −1 , while the total escape is estimated to be equal to 2.2 × 10 24 s −1 .…”

Effects of solar irradiance on the upper ionosphere and oxygen ion escape at Mars: MAVEN observations

“…The absence of an EUV dependence for fluxes of ions with E > 30 eV was one of the reasons for separation of ions into high‐ and low‐energy components. Moreover, such a separation is natural that is confirmed by analysis of ion distribution functions in the Martian tail [ Nilsson et al , ; Fraenz et al , ]. Note that the real energy of the low‐energy oxygen ions is usually lower since the ions in the tail are additionally accelerated by the spacecraft potential.…”