Reflection of solar wind protons on the Martian bow shock: Investigations by means of 3‐dimensional simulations

Abstract

The reflection of solar wind protons on the Martian bow shock (BS) is investigated by means of three‐dimensional simulation models. A two steps approach is adopted to allow a detailed analysis of the reflected population. Firstly, the 3‐dimensional hybrid model of Modolo et al. (2005) is used to compute a stationary state of the interaction of the solar wind (SW) with Mars. Secondly, the motion of test particles is followed in the electromagnetic field computed by the hybrid simulation meanwhile detection criteria defined to identify reflected protons are applied. This study demonstrates some effects of the large curvature of a planetary BS on the structure of the foreshock. Reflected protons encounter the BS in a region encompassing parts of the quasi‐perpendicular and quasi‐parallel shocks, and exit the shock mainly from the quasi‐parallel region. The energy spectrum of all reflected protons extends from 0 to almost 15keV. A virtual omnidirectional detector (VOD) is used to compute the local omnidirectional flux of reflected protons at various locations upstream of the BS. Spatial variations of this omnidirectional flux indicate the location and spatial extent of the proton foreshock and demonstrate its shift, increasing with the distance downstream, in the direction opposite to the motional electric field of the SW. Local energy spectra computed from the VOD observations demonstrate the existence of an energy gradient along the direction of the convection electric field.