Combined analysis of Far UV and Mid UV spectra obtained by the MAVEN IUVS instrument in a Stellar Occultation Mode
Résumé
In this presentation, we will focus on the results obtained by the Imaging Ultraviolet Spectrograph (IUVS) onboard the Mars Atmosphere and Volatile and Evolution (MAVEN) mission while performing stellar occultations observations. In the IUVS wavelength range, CO2 possesses a distinct and broad signature shortward of 200 nanometers which allows one to retrieve CO2 concentration and subsequently to deduce atmospheric pressure and temperature profiles from 30 to 150 km of altitude (upper troposphere up to the thermosphere) as well as the concentration of other atmospheric consitituents (clouds/aerosols, ozone and molecular oxygen). The occultation technique relies on the determination of atmospheric transmission at various altitudes above the surface. Only relative measurements are needed to infer species abundances, and thus the method is self-calibrated.The ratio of spectra taken through (close to Mars) and outside (far from Mars) the atmosphere gives an atmospheric transmission at each altitude. If any absorbing or/and scattering species is present along the optical path, photons are lost and resulting transmissions are lower than 1. The sampling rate yields a vertical resolution typically greater than 3 km on the vertical. For Mars, the sounded region inside which a quantity of atmospheric constituents can be derived lies generally between 20 and 150 km depending on the atmospheric state (dust loading). The compiled dataset has already yielded a variety of results, showing high concentrations of ozone in the deep polar night as well as the detection of a highly elevated aerosol layer potentially made of CO2 ice.