On the Temperatures of Planetary Magnetosheaths at the Subsolar Points

This research explores the relationship between the temperatures of the solar corona and planetary magnetosheaths. Based on the second law of thermodynamics, the maximum temperature of the planetary magnetosheaths cannot exceed that of the solar corona. A theoretical investigation is presented into the expansion of the solar corona, the propagation of solar wind, and the compression of planetary magnetosheaths by bow shocks. The method used is general and fits the dynamics of multiple components, thermal anisotropy, and non‐Maxwellian plasmas in the steady state, and approximate formulas are obtained. The results indicate that, for the steady state, planetary magnetosheaths at the subsolar points in the solar system have approach peak mean temperatures. Second, a systematic statistical survey of the average temperature of the planetary magnetosheaths is presented and shows that the average plasma temperature of the subsolar point magnetosheaths of Earth and Saturn are 206 eV (2.39 MK) and 171 eV (1.98 MK), respectively, which are close to that of the corona. The statistical results are consistent with the theoretical estimations. These results are of significant use for estimating the thermal properties of the planetary magnetospheres. Plain Language Summary This research focuses on the relationship between the temperatures of the planetary magnetosheaths and that of the solar corona. It is thus an interdisciplinary problem in solar‐terrestrial physics. A theoretical investigation is presented on the expansion of the solar corona, the propagation of the solar wind, and the compression of the planetary magnetosheath by bow shocks. An approximate formula for the relationship between the temperatures of the solar corona and that of planetary magnetosheaths is obtained. The quantitative results indicate that the peak temperature of the planetary magnetosheaths are comparable and approach that of the solar corona. A statistical investigation is made of the average temperatures of the magnetosheaths of several planets, and it shows that, although the proton temperatures are several times the electron temperatures, the average plasma temperatures of the magnetosheaths of Earth and Saturn are almost the same as that of the solar corona. This work advances our understanding of the thermal properties of planetary magnetosheaths and also advances research into the formation of plasma sheets. Key Points A quantitative relationship between the temperature of the steady