Using Solar Wind Helium to Probe the Structure and Seasonal Variability of the Martian Hydrogen Corona

Abstract

We utilize measurements from instruments on the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission to investigate singly ionized helium formed by charge exchange between solar wind alpha particles and neutral hydrogen in the region upstream from Mars. We show that the observed helium ion signal varies with solar wind speed and spatial location in a manner consistent with expectations for a charge exchange source. We find that the ratio of singly to doubly ionized helium varies with Martian season, with a peak in the southern summer season. The inferred neutral hydrogen column density and the seasonal variation thereof agree with the results of previous studies based on other measurement techniques. The MAVEN helium ion measurements provide a new method of probing the hydrogen corona, with nearly continuous coverage of the Martian seasonal cycle across the entire mission, enabling study of the interannual variability of the Martian exosphere.