Planetary ions acceleration in a hot flow anomaly at Mars

Previous observation of a single hot flow anomaly (HFA) at Earth by MMS mission reported solar wind protons effective acceleration inside these structures to nearly 1 MeV under certain conditions via first-order Fermi acceleration process. Current study focuses on the analysis of a single HFA registered at Mars by MAVEN spacecraft. The event is characterized by the presence of accelerated O+ and O2+ ions of planetary origin on both sides from the current sheet associated with the event. Ions with energies up to ∼10 keV are detected before the current sheet crossing, and over 30 keV after the current sheet crossing. We report that the relationship between the ion mass and the maximum energy to which acceleration occurs is consistent with the above-mentioned Fermi acceleration process. We hypothetize that effective planetary ions acceleration in HFAs is possible only at unmagnetized planets due to closer bow shock stand-off distance.