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.

According to the different orientations of the interplanetary magnetic field (IMF), the planetary shock can be either quasi-parallel or quasi-perpendicular. Under quasi-parallel conditions a significant number of solar wind suprathermal particles are reflected from the shock and drift along IMF, forming an extended and highly turbulent region called the foreshock where various nonlinear plasma phenomena are observed. In this research, we perform a case study of the structures in the foreshock region at Mars observed by Mars Atmosphere and Volatile Evolution (MAVEN). We use data from plasma analyzer STATIC and magnetometer MAG to analyze ion beams angular spectrum and magnetic field dynamics. We show that the observed structures are consistent with Short Large-Amplitude Magnetic Structures (SLAMS), commonly detected in foreshock regions of magnetized and unmagnetized bodies throughout the Solar system. Finally, we calculate the magnetic Mach number to analyze the characteristics of the observed foreshock structures. The analysis shows, that SLAMS are formed by the resonance between plasma waves propagating along the IMF and the backstreaming scattered solar wind H+ and exospheric O+ and O2+ ions, with the dominant impact of O2+ ions.