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Investigation of the Martian Lower Exosphere Using MAVEN IUVS Periapsis Observations

Presentation #206.02D in the session “Mars: From the Surface to the Atmosphere”.

Published onOct 03, 2021
Investigation of the Martian Lower Exosphere Using MAVEN IUVS Periapsis Observations

Atomic hydrogen (H) escape is an important tracer of water loss from the Martian atmosphere. Reliable estimates of the density and temperature of H in the lower thermosphere and exosphere are required to constrain the present-day water escape from Mars. In this work, we derive the H density using the resonantly scattered H Lyman-alpha emission (121.6nm) observed across the limb during periapsis by the Imaging UltraViolet Spectrograph (IUVS) instrument onboard NASA’s MAVEN spacecraft. We isolate the Lyman-alpha intensity from exospheric hydrogen by subtracting the contribution from the interplanetary H (IPH) background using the model by Pryor et al [1992]. As Lyman-alpha is an optically thick emission, we use a sophisticated radiative transfer model to derive the H density independent of the instrument calibration and incident solar flux. The retrieved densities are sensitive to the specification of background temperature, which we derive from an analytical fit to the IUVS-derived temperature data. We will report results that demonstrate the reconciliation of IUVS temperature and Lyman-alpha intensity. In doing so, we will compare different methods of fitting the background temperature profile and its effect on the derived H density and escape flux. In addition, we will also present evidence for the seasonal, solar cycle and sporadic dust storm variability in the derived hydrogen density and thermal H escape flux at the Martian exobase. Our results advance the understanding of the Martian thermosphere and lower exosphere and demonstrate a pronounced effect on the rate of water escape through the Martian exosphere.

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