Ionospheric erosion at Mars caused by interplanetary coronal mass ejections

The loss of Mars' ionosphere over the history of the planet is thought to have contributed significantly to the evolution of the Martian climate. The detailed effects of large, transient solar events, such as interplanetary coronal mass ejections (ICMEs) on ionospheric escape rates at Mars are still largely unknown. Although past studies have shown that such events tend to enhance the escape rate of planetary ions from Mars, these studies used measurements from missions that did not make observations in the lower ionosphere and exobase regions. Thus, these studies were unable to unravel the full set of physical processes driving the escape observed at higher altitudes, particularly across the exobase region, below which most planetary ions originate. In this study, we will discuss the MAVEN observations from the two CMEs that impacted Mars during March 2015 and September 2017. Although the MAVEN periapsis was near the terminator for both events, these are the largest ICME-driven space weather events observed by MAVEN to date for which ionospheric observations exist down through the exobase region. Substantial erosion of ionosphere occurs at high altitudes, but this study focuses on whether significant erosion occurs at or below the exobase. If present, such erosion could have significant importance for atmospheric evolution over time, as these erosion events would have access to a large reservoir of ionospheric ions.