Ion velocity distributions upstream from the Martian bow shock: Recent results from MAVEN

The region upstream from the bow shock of Mars is rich in different particle populations along with the associated physical processes. The MAVEN Solar Wind Ion Analyzer (SWIA) measures ion velocity distributions with unprecedented time and angular resolution, enabling the first detailed investigation of ion populations. Analysis of the distributions reveals, in addition to the solar wind plasma, the presence of pickup ions and another suprathermal population. The latter is observed only along interplanetary magnetic field lines connected to the Martian bow shock, i.e. inside the foreshock. Further analysis of the reduced velocity distributions shows that the total distribution of the velocity component parallel to the ambient magnetic field is generally well fitted by three Maxwellian components, except when a high-energy tail is present. This is the first time that the physical characteristics of the non-thermal populations can be precisely determined at Mars, including their density, velocity and thermal width. These determinations enable to explore in depth the production mechanisms of the suprathermal populations and their relevance in wave-particle interaction. This provides a new venue to explore the relative impact of the exosphere and the bow shock on the upstream Martian environment.