First Direct Observations of the Velocity Distribution, Emission and Thermal Properties of Hot H at Mars
Résumé
Water loss from Mars occurs through multiple channels that include the thermal and supra-thermal (hot) hydrogen atom escape from the planet’s exosphere. The echelle mode of the MAVEN imaging spectrograph has a sufficiently high spectral resolution that could theoretically identify the thermal profile of hot H atoms in the Martian atmosphere. Data obtained with this mode has recently shown unexpected Lyman-α signatures during special calibration campaigns when the instrument line of sight is pointed away from the planet. These spectral data have been analyzed and can be explained as emissions from the hot H population around Mars where, in this observing geometry, the thermal population of H atoms is at a minimum and the Doppler shifted emissions from the hot H population are more visible in the combined emission profile. This study shows the velocity, thermal, brightness, and spatial distribution of supra thermal H atoms for the first time, as measured from Mars' orbit, and discusses implications for H escape.