New Observations of Molecular Nitrogen by the Imaging Ultraviolet Spectrograph on MAVEN

The Martian ultraviolet dayglow provides information on the basic state of the Martian upper atmosphere. The Imaging Ultraviolet Spectrograph (IUVS) on NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission has observed Mars at mid and far-UV wavelengths since its arrival in September 2014. In this work, we describe a linear regression method used to extract components of UV spectra from IUVS limb observations and focus in particular on molecular nitrogen (N[SUB]2[/SUB]) photoelectron excited emissions. We identify N[SUB]2[/SUB] Lyman-Birge-Hopfield (LBH) emissions for the first time at Mars and we also confirm the tentative identification of N[SUB]2[/SUB] Vegard-Kaplan (VK) emissions. We compare observed VK and LBH limb radiance profiles to model results between 90 and 210 km. Finally, we compare retrieved N[SUB]2[/SUB] density profiles to general circulation (GCM) model results. Contrary to earlier analyses using other satellite data that indicated N[SUB]2[/SUB] densities were a factor of three less than predictions, we find that N[SUB]2[/SUB] abundances exceed GCM results by about a factor of two at 130 km but are in agreement at 150 km.