Tianwen-1 and MAVEN Observed Multiple Ion Escape Channels of Mars during an Interplanetary Coronal Mass Ejection

Abstract

Interplanetary coronal mass ejections (ICMEs) are solar transients that have significant effects on the Martian space environment. The simultaneous spacecraft observations from Tianwen-1 and Mars Atmosphere and Volatile Evolution (MAVEN) are used to study the planetary ion escape for a dramatic ICME. MAVEN passes through the upstream solar wind, +E hemisphere, and -E hemisphere in one orbital period at 20:00 UT -24:00 UT on 2022 April 24. During this period, the interplanetary magnetic field (IMF) remained stable and dominated by the +Y component. In addition to the well-known “plume” escape channels located in the +E hemisphere, MAVEN also observed one ion escape channel in each hemisphere. The additional escape channel located in the +E hemisphere was easily identified as ionized atoms originating from the exosphere, which became significant during CME and was first reported. These ions are observed in both the solar wind and the magnetosheath, and the observed flux of these ions is strongest when MAVEN is very close to the upstream of the bow shock. In this event, ion density of this channel is up to 0.03 cm-3, which is 10 % ~ 30 % of the observed plume. The escape channel structure in the -E hemisphere is complex, and MAVEN has insufficient observation of this channel due to its orbital inclination. Tianwen-1 provided a powerful supplement based on the 1.5 hr observation of this structure, revealing many characteristics of this escape channel. The channel in the -E hemisphere also shows a narrow band in the energy spectrum, similar to the plume. Moreover, its density is between the ion densities of the two +E hemispherical channels. Interestingly, it is more likely to be observed near the magnetic pileup boundary rather than the entire -E hemisphere magnetosheath. These new channels reveal more details of Martian ion escape. The solar wind conditions similar to the early solar system during the ICMEs also help to study the early evolution of Mars.