Mars Express/SPICAM UV Spectrometer: First observation of an auroral emission in the martian atmosphere

Abstract : During orbit 716 of Mars Express mission, the clear identification of an auroral type emission has been done by SPICAM UV spectrometer. A significant increase of the measured emission has been observed during 7 seconds on the martian nightside. This increase of the emission is not similar than the already well-identified nightglow emission [1]. It is composed of the CO 4+ bands, of the C 156.1 and 165.7 nm, of the CO Cameron bands, of the CO2+ doublet at 289.0 nm and of the O (297.2 nm) emissions which classically composed the martian dayglow. Thanks to the property of SPICAM spectrometer we are also able to estimate the position and altitude of this emission along SPICAM field of view. The very high correlation between this position and the presence of the highest crustal magnetic field structures identified at Mars [2] strongly suggests the role of these structures in driving the incident electrons at the origin of these emissions. It is a strong identification of very localized peak of ion density on the martian nightside in the region of crustal magnetic field and also of the importance of the crustal field in driving the nightside ionosphere.