Mass Composition of the Escaping Flux at Mars: MEX Observations

Abstract

AbstractUsing more than 7 years of ion measurements from the ASPERA‐3/IMA instrument onboard the Mars Express mission, we analyze the mass composition of the two main outflowing heavy ion species O and O+. Using an improved multispecies fitting technique, we discriminate the molecular from atomic oxygen ion population. We find that the low‐energy ions (3.2–100 eV) dominate the heavy ion population downstream of the induced magnetospheric boundary, where the mean ratio of O relative to O+ is 0.76 (averaged over the low‐energy range and all observed directions). The spatial distribution of the O /O+ ratio for the near‐Mars environment shows that very close to the planet O is somewhat more abundant in part of the dayside. The same trend is even clearer in the central tail up to distances of 1.2RM from the center of the tail. In contrast, O+ is more abundant in the terminator region and the mantle just inside the induced magnetospheric boundary. O+ is typically more abundant in the magnetosheath.