A Comparative Analysis of the Venus and Mars Magnetotail ion Flows. First Data From the IMA (ASPERA-4, Venus Express) Mass Spectrometer Compared With Mars Express.

The first data from the IMA mass spectrometer aboard the Venus Express (VEX) probe arrived on May 15 2006, almost 2 years after the first data from an identical instrument aboard Mars Express (MEX). Now we understand relatively well the Martian plasma environment, and we can compare it with the new data from Venus. For this we extracted data from similar parts of the MEX and VEX orbits, and analysed the mass and energy spectra of planetary and magnetosheath ions at comparable locations of the planetary environments. We can see that the magnetotails of both planets consists of several plasma regimes which are spatially organized in the reference frame defined by the interplanetary magnetic and electric fields. The central part of the tail (Plasma Sheet) contains ions of planetary origin, accelerated to about 1keV, and the periphery of the tail is filled with dispersed plasma structures which include a very low energy component. The geometry of the tails and the ion compositions differ at Mars and Venus. Present work shows results from case studies and a statistical study.