Precipitating Solar Wind Hydrogen as Observed by the MAVEN Spacecraft: Distribution as a Function of Column Density, Altitude, and Solar Zenith Angle

Abstract

The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission observes precipitating solar wind hydrogen ENAs in the upper Martian ionosphere with various instruments onboard. These precipitating solar wind hydrogen atoms result from the direct interaction between the solar wind and Mars's extensive hydrogen corona, creating a beam of particles traveling at solar wind speed that can penetrate deep into the ionosphere of Mars. Using particle data collected by both the Solar Wind Ion Analyzer (SWIA) and Neutral Gas and Ion Mass Spectrometer (NGIMS) onboard MAVEN, we seek to characterize the global behavior of these particles. By using a combination of energy spectra and neutral gas density data, we are able to determine the behavior of this particle population as a function of altitude, column density, and solar zenith angle. Through our analysis, we see that these precipitating solar wind hydrogen ENAs undergo multiple charge exchange interactions and ultimately scatter significantly at an altitude of 160 km or column density of 5 × 1016 cm−2. This observed column density at which equilibrium is reached is at a value ∼17 times greater than the theoretical value. We also demonstrate that this particle population's energy flux follows a cosine dependence of solar zenith angle, as is predicted by models.