Analysis and Modeling of HST Observations of the Martian Exosphere

We present an analysis of HST ACS/SBC UV images of the extended hydrogen Lyman alpha emissions from the Martian Exosphere obtained during Oct/Nov 2007 using a radiative transfer code developed by our group. This code corrects for multiple scattering effects in the atmosphere of Mars. We assume a spherically symmetric atmosphere and have used the standard Chamberlain approach to model the exospheric number density profile. For the lower part of the atmosphere, we have used a simplified diffusion model with only diffusion of H in carbon di-oxide for constructing a number density profile of H. By varying the temperature of the hydrogen population at the exobase and their number densities, we obtain the best fit to the data. We observe that there was a 40% decrease in brightness in the data, which correlates to almost a factor of 10 decrease in number density in just a span of a month. We also calculate the escape flux of hydrogen based on the modeled exobase temperature and number densities, which could then be related to the amount of water lost from Mars