Survey of the nitric oxide ultraviolet emissions by Mars Express and implications for the Martian upper atmosphere dynamics.
Friday, 19 December 2014
In the upper atmosphere of Mars, CO2 and N2 are photodissociated by solar UV and EUV on the dayside, producing N and O atoms. They are carried to the nightside by the general circulation in the Martian upper atmosphere. They recombine to form nitric oxide molecules (NO) in the C2∏ excited state that relax to the ground state (X2∏) by emission of UV delta and gamma bands. This nightglow is an important tracer of thermospheric horizontal and vertical circulations. We combine two types of SPICAM observations performed in two different modes modes (limb viewing and stellar occultations) to build a large dataset of nitric oxide observations. The detection (or non-detection) of this nightglow provides important information of the dayside-to-nightside summer-to-winter global circulation in the upper atmosphere of Mars. We build a map of the location of the detection of the nitric oxide emissions at different seasons and Martian years. We furthermore study the location and brightness of the peak of the vertical emission profile. Finally, the influence of the solar cycle on the emission is analysed.