Hydrogen Escape Rates 2021-2023 Retrieved from Emirates Mars Mission Observations

<p>The surface of the planet Mars exhibits a record of dessiccation and oxidation, the legacy of significant water escape to space as hydrogen and oxygen. This H escape can be constrained using ultraviolet observations of the planet's upper atmosphere, where neutral atomic hydrogen scatters UV sunlight. In the time since its orbit insertion in early 2021, the Emirates Mars Ultraviolet Spectrometer (EMUS) on the Emirates Mars Mission (EMM) has been observing this hydrogen at 102.6 nm and 121.6 nm, H Lyman beta and Lyman alpha. Here we present H escape rates retrieved from these observations, obtained using a 3D radiative transfer model that simulates the brightness of both spectral lines, combining their information content to constrain the atmospheric state. In agreement with past results, we find that H escape peaks around Southern Summer solstice, after perihelion, exhibiting a more than 10x increase relative to Northern Summer conditions. Importantly, our retrievals extract information about both the hydrogen density and temperature, and do not require independent assumptions about the upper atmosphere temperature. We will discuss prospects for extending these retrievals beyond the current EMM dataset as well as implications for the long-term evolution of the Mars atmosphere.</p>