Study of the Martian cold oxygen corona from the O I 130.4 nm by IUVS/MAVEN

Abstract : The observations of the O I 130.4 nm resonant line performed by the Imaging Ultraviolet Spectrograph (IUVS) aboard the Mars Atmosphere and Volatile Evolution Mission (MAVEN) are presented. This emission line is observed during the different orbit phases of MAVEN : disk observations at apoapsis, limb scans at periapsis and coronal scans during the outbound orbit leg. The atomic oxygen density which is an important parameter to understand the heating, composition, dynamics of the Martian upper atmosphere and the temperature at 200 km are retrieved from an automatic inversion algorithm. A set of observations performed by IUVS during the first months of the mission are analyzed to study the variabiity of the atomic oxygen in the Martian upper atmosphere. The derived oxygen density and the temperature at the exobase are in the predicted range (107 - 108 cm-3; 200 – 300K) by the current thermospheric models of Mars. The derived parameters are very sensitive to the absolute calibration of the instrument which is the main source of uncertainty on the results presented.