Protons precipitation onto the Martian atmosphere: Mars Express observations

It is the first study of the intrusion of the solar wind protons into the Martian atmosphere. Using data of the ASPERA-3/Mars Express instrument, we have studied two orbits where the H+ precipitation happened on the dayside close to the subsolar point. We have shown that: a part of the observed protons indeed precipitates, above weak and/or cusp-like crustal magnetic anomalies, even for a nominal solar wind, and we have measured energy fluxes and particle fluxes of 108-109 eV/cm2/s and 105-106 H+/cm2/s, respectively. The proton precipitation is a kinetic effect due to a small size of the Martian magnetosheath with respect to the proton gyroradius.