Investigating Seasonal Variations in Mars' Hydrogen Escape Flux derived by model fitting Lyman Alpha observations from Emirates Mars Ultraviolet Spectrometer (EMUS) onboard the Emirates Mars Mission (EMM).

Abstract

The Martian atmosphere has undergone significant decay over time, with several factors contributing to this process. It is believed that thermal (Jeans) escape is a significant contributor to hydrogen loss on Mars (Chaufray, 2021). In this research, the role of thermal (Jeans) escape in the uplifting of hydrogen molecules to the exosphere, driven by solar wind forcing, is investigated on seasonal bases. Studying hydrogen escape seasonally can provide insights into the role of solar forcing in atmospheric processes. This research utilizes observations from the Emirates Mars Ultraviolet Spectrometer (EMUS) onboard the Emirates Mars Mission (EMM) To study the atmospheric Hydrogen Lyman Alpha emission on seasonal timescales. The data for this study focuses on the perihelion (greater than Ls 225) and aphelion (between 60-90 Ls)  periods, during which variations in the escape flux due to exobase temperature changes are expected. Level 2b/2a data is specifically chosen because it includes calibrated brightness and added geometric data, a combination of different EMUS observation modes is used in the study. The Lyman Alpha brightness measurements are used to derive the density profile of hydrogen in the Martian atmosphere using the same approach described in (Chaufray, 2008). The atmospheric model is divided into two parts, below the exobase the hydrogen density is described by a diffusive model, while above it uses Chamberlain’s model without satellite particles (Chamberlain, 1963). Deriving atmospheric hydrogen density profile is done by assuming the exobase temperature and solving radiative transfer equations to compute theoretical intensities which are then fitted with observational data to determine exobase temperature and density, a reasonable fit of observations is done assuming the parameters are in ranges that are in line with photochemical models (Krasnopolsky, 2002). This approach has been used to analyze the Mariner 6, 7 exospheric Lyman-α data during the late 1960s (Anderson and Hord, 1971), and the same approach has been used to analyze SPICAM Lyman-α data on Mrs express (Chaufray, 2008), this research attempts to use the same approach to analyze EMUS Lyman-α observations. It is expected that the (Jeans) escape flux of Hydrogen will vary on seasonal timescales, with higher escape fluxes observed around the perihelion period when the exobase temperature is the highest. This is due to the fact that the (Jeans) escape mechanism is driven by the temperature of the exobase, with higher temperatures resulting in higher escape rates. On the other hand, it is expected that lower escape fluxes will be observed during the aphelion period when the exobase temperature is lower.