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- Title
Using Solar Wind Helium to Probe the Structure and Seasonal Variability of the Martian Hydrogen Corona.
- Authors
Halekas, Jasper S.; McFadden, James P.
- 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. Plain Language Summary: Thanks to Mars' small size and weak gravity, the upper reaches of its atmosphere extend far above the surface. The lightest element, hydrogen, forms a corona around Mars many times larger than the planet. The solar wind that flows from the Sun, composed mainly of protons and alpha particles (doubly ionized helium), interacts directly with this hydrogen corona. Reactions between solar wind alpha particles and neutral hydrogen in the corona can form singly ionized helium. We utilize measurements from instruments on the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission to investigate the singly ionized helium signature in the region upstream from Mars. We show that the measured signal varies with solar wind speed and distance from Mars as expected, and utilize it to probe the structure and seasonal variability of the Martian hydrogen corona. These measurements will ultimately allow us to better understand the Martian seasonal cycle and its role in the escape of hydrogen from the Martian atmosphere. Key Points: Singly ionized helium is produced upstream from Mars by charge exchange between solar wind alpha particles and Martian neutral hydrogenThe observed ratio of singly to doubly ionized helium varies as expected with solar wind speed, spatial location, and Martian seasonHelium ion measurements can be utilized to estimate the column density of hydrogen in the Martian corona and its seasonal variability
- Subjects
SOLAR wind; HELIUM; EXOSPHERE; MARTIAN atmosphere; ALPHA rays
- Publication
Journal of Geophysical Research. Planets, 2021, Vol 126, Issue 11, p1
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2021JE007049