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- Title
Precipitating Solar Wind Hydrogen at Mars: Improved Calculations of the Backscatter and Albedo With MAVEN Observations.
- Authors
Girazian, Z.; Halekas, J.
- Abstract
Outside the Martian bow shock, charge exchange between solar wind protons and exospheric hydrogen produces energetic neutral atoms (ENAs) that travel toward Mars at the solar wind velocity. The penetrating ENAs deposit most of their energy near 150 km, but a fraction of them undergo enough collisions to be scattered back to space, resulting in a hydrogen albedo. Some of the penetrating ENAs are converted into protons upon reaching the collisional upper atmosphere. These protons can be measured by the Mars Atmosphere and Volatile EvolutioN's Solar Wind Ion Analyzer (SWIA) during periapsis passes, providing information about the penetrating and backscatter populations. In this work, we perform the first detailed analysis of the backscatter and albedo using SWIA observations. We find that our calculated backscatter energy spectra are consistent with model predictions and that, as expected, the penetrating and backscatter particle fluxes increase with solar wind speed and decrease with solar zenith angle (SZA). We also find that the albedo, which has an average value of 0.20 ± 0.16, decreases with solar wind speed and increases at high SZAs near the terminator. Plain Language Summary: Hydrogen atoms in the uppermost region of Mars' tenuous atmosphere extend far into space, where they are directly exposed to the incoming solar wind. Protons in the solar wind collide with the hydrogen, producing high‐speed neutral atoms that travel into the atmosphere of Mars. While some of the high‐speed atoms deposit energy into the upper atmosphere, others undergo enough collisions with atmospheric gases to be reflected back to space. In this paper, we present a detailed study of the reflected particles using observations from the Mars Atmosphere and Volatile EvolutioN mission. We show that there is a larger fraction of reflected particles at high solar zenith angles and at low solar wind speeds. We also find that the energies of the reflected particles are consistent with predictions from models of the Mars‐solar wind interaction. Key Points: We present new calculations of the hydrogen backscatter and albedo using low altitude proton measurements from MAVENOur calculated penetrating and backscatter energy spectra are consistent with model predictionsIn agreement with expected trends, the albedo decreases with solar wind speed and increases with solar zenith angle
- Subjects
BOW shock (Astrophysics); SOLAR wind; MARS Atmosphere &; Volatile Evolution (Artificial satellite); ARTIFICIAL satellites; MARS probes
- Publication
Journal of Geophysical Research. Planets, 2021, Vol 126, Issue 2, p1
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2020JE006666