Simultaneous study of charge exchange at Mars with XMM-Newton and Mars Express

We propose to utilize the unique opportunity provided by the presence of MarsExpress for the first ever combination of remote Xray observations of solarwind charge exchange (SWCX) emission with simultaneous measurements of the solarwind at Mars. XMMNewton is by far the best Xray satellite for this kind ofstudy. In a previous Mars observation, it has already provided the first direct,unambiguous detection of SWCX emission from the exosphere of another planet.This finding has consequences for Xray astrophysics in general (plasmadiagnostics and soft Xray background), and is important for planetary evolution(atmospheric outgassing). It opens up a novel possibility of remote globalimaging of planetary exospheres and their spatial and temporal variability. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]