Titan's emission processes during eclipse

Observations of Titan's emissions during its 2009 eclipse by Saturn revealed a weak airglow around the moon, as well as a brighter emission from its disk (West et al. [2012]. Geophys. Res. Lett. 39 (1), 18204). We explore here the potential mechanisms that could generate these emissions and more specifically the role of magnetospheric plasma and cosmic rays in the upper and lower atmosphere, respectively. We consider excitation of N2 by these energy sources and calculate the resulting emissions through a detailed model of N2 airglow followed by careful radiation transfer of the emitted photons through the atmosphere, and into the UVIS and ISS instruments. Our results indicate that the observed limb emissions are consistent with magnetospheric plasma energy input, while emissions instigated by cosmic ray excitation are very weak and cannot explain the observed disk emissions. We discuss possible contributions from other sources that could potentially explain the disk observations. The most likely scenario is that of scattered stellar light from Titan's disk.