The first EMM/EMUS stellar occultation measurements of the Martian atmosphere in both extreme and far ultraviolet wavelengths

The major scientific objective of the Emirates Mars Mission (EMM) is to explore the global atmospheric dynamics of the Martian atmosphere both in short term (diurnal) and long term (seasonal). The Emirates Mars Ultraviolet Spectrometer (EMUS) instrument on board the EMM makes two-dimensional images ( in extreme and far ultraviolet wavelengths: 90-170 nm) of the Martian disk and exosphere to characterize the neutral densities in the thermosphere and exosphere of Mars. In this paper, we will present the first results from the stellar occultation measurements made by the EMUS instruments in October 2022. These occultation observations were not part of the original science planning and were added as a bonus EMM science. A total of seven stellar occultations were performed during the two EMM orbits spanning between 24 to 27 October. These measurements were the first stellar occultation of Mars in the EUV wavelengths (90-110 nm). Due to the higher sensitivity of the EMUS instrument, the occultation measurements were able to probe the atmosphere with an altitude sampling of 2 km or lower. The occultation measurements by SPICAM/MEx and IUVS/MAVEN were limited to 160 km due to wavelengths limited to a longward of 110 nm.  However, the use of EUV wavelengths in the EMUS stellar occultation provided atmospheric probing up to 190 km thus enabling neutral density retrieval up to the exobase region of Mars. The CO₂ densities are retrieved from 90-185 km and the temperature profiles were retrieved using the constraint of hydrostatic equilibrium to the CO₂ densities. We shall discuss results from the EMUS occultation campaign specifically the observed variability in the CO₂ density and temperature during the occultation campaign.