Deriving Neutral Density Profiles of the Mars Atmosphere from MAVEN/SEP Measurements of Scorpuis-X1 X-ray Occultations

The Solar Energetic Particle (SEP) instrument onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft utilizes a set of solid state detectors designed to measure energetic particles, including electrons, protons, and photons. Scorpius X-1 is the brightest extrasolar X-ray source in the sky in the 10-20 keV energy range; MAVEN/SEP is able to detect these photons. Occultations of the X-rays from Scorpius X-1 in the atmosphere of Mars and detected by MAVEN/SEP can be used to gain insights into the Mars neutral densities and temperatures. In this work, we study the energy and field of view response of the SEP instrument to Scorpius X-1 X-rays for all of MAVEN/SEP's 12 silicon detectors. A theoretical model of the X-ray occultation light curve is developed, based on the appropriate X-ray cross sections for CO2 and Ar, and on the calculated neutral column densities along the line of sight. A set of model light curves is calculated for a range of atmospheric neutral densities and temperatures and the results are compared to the occultation data in order to derive neutral density profiles of the Mars atmosphere in the 50-100 km altitude range that best fit the measurements. Preliminary analysis of 11 consecutive MAVEN orbits during 12-13 March 2018 containing X-ray occultations indicates that the reconstructed neutral density profile acquired from our fitting routine matches the seasonal temperature conditions expected for the studied time period.