Solar wind interaction with the Martian upper atmosphere: Roles of the cold thermosphere and hot oxygen corona

TL;DR

This study uses advanced modeling to explore how the Martian thermosphere and exosphere influence ion escape and the planet's interaction with solar wind, highlighting the roles of hot oxygen and cold thermospheric oxygen.

Contribution

It introduces a multifluid MHD model combining 3D thermosphere and exosphere data to better understand Martian ion escape mechanisms and solar wind interactions.

Findings

3D hot oxygen corona reduces escape of planetary ions.

Ion escape rates are similar for 1D and 3D models but 3D better matches observations.

Cold thermosphere is the main source of escaping O+ ions during weak solar activity.

Abstract

We study roles of the thermosphere and exosphere on the Martian ionospheric structure and ion escape rates in the process of the solar wind-Mars interaction. We employ a four-species multifluid MHD (MF-MHD) model to simulate the Martian ionosphere and magnetosphere. The $cold$ thermosphere background is taken from the Mars Global Ionosphere Thermosphere Model (M-GITM) and the $hot$ oxygen exosphere is adopted from the Mars exosphere Monte Carlo model - Adaptive Mesh Particle Simulator (AMPS). A total of four cases with the combination of 1D (globally averaged) and 3D thermospheres and exospheres are studied. The ion escape rates calculated by adopting 1D and 3D atmospheres are similar; however, the latter are required to adequately reproduce MAVEN ionospheric observations. In addition, our simulations show that the 3D hot oxygen corona plays an important role in preventing planetary molecular ions (O$_2^+$ and CO$_2^+$) escaping from Mars, mainly resulting from the mass loading of the high-altitude exospheric O$^+$ ions. The $cold$ thermospheric oxygen atom, however, is demonstrated to be the primary neutral source for O$^+$ ion escape during the relatively weak solar cycle 24.