Plasma Temperatures in the Martian Subsolar Magnetosheath: MAVEN Observations

Abstract

We studied the thermal features of magnetized plasmas in the Martian subsolar magnetosheath using MAVEN’s observations from 2014 to 2019. Statistical analyses show that the average ion and electron temperature in the Martian subsolar magnetosheath are 210 and 31 eV, respectively, which are significantly lower than their counterparts in the subsolar magnetosheaths of Earth and Saturn which both have an inherent magnetosphere. However, the ratio T¯i/T¯e in the Martian subsolar magnetosheath is about 6.8, which is very close to that of Earth and Saturn. We further investigated the relationship between Ti/Te and the bulk ion flow velocity Vi, as well as the relationship between the total plasma beta β and Vi. Results show that the average value of Ti/Te when Vi<300km/s is considerably higher than when Vi>300km/s. A value of Vi closer to 250–300 km/s leads to a higher average value of the total plasma beta β. These results confirm the prediction of previous researchers, that there is not enough room for solar wind thermalization as the distance between the Martian bow shock and the so-called obstacle is of the order of a solar wind proton gyroradius.