Seasonal and Mach Number Variation of the Martian Bow Shock Structure

Like its terrestrial counterpart, the Martian bow shock can exhibit foot, ramp, and overshoot substructures. The shock extent is known to vary with solar wind and season, but it remains an open question whether other features of the bow shock also vary seasonally. By comparing parameters of the shock during different seasons and solar wind conditions, we investigated whether the presence of seasonal planetary ions has any effect on the shock structure. We utilized a series of algorithms to automatically collect and analyze 7056 shock crossings from MAVEN spacecraft data between November 2014 and 2019. We compared the magnetic shock jump and overshoot amplitude as functions of upstream parameters and season. We found that the magnetic shock jump agrees to first order with Rankine-Hugoniot predictions, and that the overshoot amplitude dependence on critical ratio, beta and Alfven Mach number agree with the results of previous studies. These trends are identical for all seasons. We also found that the shock jump and fast Mach number correlate primarily with solar zenith angle, whereas overshoot amplitude correlates primarily with shock extent. We found that the most likely cause of the latter was an unexpected strong correlation between overshoot amplitude and the solar wind flow fast Mach number. The seasonal variability of the Sun-Mars system does not appear to be strongly reflected in the resulting shock structure. The bow shock structure is controlled mainly by the properties of the solar wind, rather than by Mars' location in its orbit around the Sun.

Automated summary

The structure of the Martian bow shock is mainly controlled by the properties of the solar wind, rather than by the seasonal variability of the Sun-Mars system.