Martian Ion Escape Variations with Solar EUV from MAVEN Observations

We have studied the O+ ion escape at Mars based on MAVEN data from two 3-month time periods with high and low EUV conditions [Dong et al., 2017], which shows that the total escape rate increases with solar EUV while the plume and tailward escaping ions respond differently to the EUV variation. However, the detailed quantitative relationships between ion escape rates and solar EUV are not established yet. We will extend this study by surveying nearly 4-year MAVEN data all through the mission. For the time periods when the spacecraft does not go outside the bow shock, there have been IMF and solar wind proxies developed from MAVEN data taken inside the bow shock. We will use both IMF data and proxies to organize all planetary ion data in the MSE coordinate system. With significantly improved data coverage, we will be able to quantify the ion escape variations with solar EUV for different escape channels (plume and tail), ion species, and energy ranges. Our initial results show that the dependence of ion escape rates on EUV may not be linear or even monotonic. This new study will provide new insights into the detailed quantitative relationships between ion escape rates and solar EUV as well as the mechanisms of how EUV affects different escaping ion populations at Mars.