Plasma Moments in the Environment of MarsMars Express ASPERA-3 Observations

We present the first electron and ion moment maps (density, velocity and temperature) of the martian plasma environment, using data from the ELS and IMA sensors of the ASPERA-3 experiment onboard Mars Express. Moments are calculated by integration and by Gaussian fits to the phase space distribution. The methods of calculation and the calibration parameters relevant for the calculation are described in detail in the first part of the paper. The estimation of ionospheric electron densities assumes that the thermal electron temperature can be determined by the instrument – despite a cut-off by a negative spacecraft potential. The spacecraft potential is estimated by the location of photoelectron peaks in the energy spectrum. For the magnetosheath we separate the low energy part of the electron spectrum – presumably spacecraft photo electrons and the high energy part. For ions, we present maps for solar wind protons and alpha particles. Protons with energies below 500 eV which may play an important role in the ionosphere are not measured by the instrument. As well the low speed solar wind protons are not sampled very well. The maps reveal all the boundaries of the Mars-solar wind interaction and give a good qualitative description of the plasma behavior at the different interaction regions.