Precipitating Solar Wind Hydrogen at Mars: Improved Calculations of the Backscatter with MAVEN Observations

Abstract:

Outside the Martian bowshock, solar wind protons charge exchange with hydrogen atoms in the extended exosphere to produce a population of energetic neutral atoms (ENAs) that stream towards Mars at the solar wind speed. The penetrating ENAs deposit most of their energy in the collisional upper atmosphere near 150 km, but a fraction of them undergo enough collisions to be scattered back to space. Both the penetrating and backscatter populations can be characterized using low altitude proton measurements made by MAVEN’s Solar Wind Ion Analyzer (SWIA). We developed a new method to calculate penetrating and backscatter energy spectra with SWIA observations. The ratios between our backscatter and penetrating spectra are smaller than suggested by previous work, and more consistent with model predictions.