Investigating Titan Airglow’s Sources, Using the Imaging Capability of the Cassini-UVIS Instrument

Abstract:

The Ultraviolet Imaging Spectrograph (UVIS) instrument includes two spectrographic channels that provide both images and spectra covering the wavelength ranges from 56 to 118 nm (EUV) and 110 to 190 nm (far-UV). While previous studies focused on analyzing spectra, very few have used the capability of UVIS to produce images. This approach allows for the investigation of a much wider set of observations (currently about 10,000 over 10 years of data). A big data analytics approach narrows the number of observations for more specific applications and detailed spectral analysis.

Previous studies on a reduced set of UVIS observations have demonstrated that dayglow emissions are at least a factor of ten brighter than the nightglow and are predominantly excited by solar photoelectrons. On the other hand, energetic Saturnian magnetosphere-plasma interactions with Titan’s ambient neutral species are a significant source of UV nightglow emissions. Magnetosphere particle interactions, particularly the particles H⁺ and O⁺, along with secondary electrons, produce a nightglow spectrum.

Our preliminary results from the UVIS images show that the airglow is highly variable in intensity and nightglow emissions are sporadic. We investigate here the various sources of nightglow to relate the nightglow spatial distribution and occurrence to the orbital position. We also present a case study where UVIS observed an airglow brightening, with an enhanced intensity over a short period of time (15 minutes). Further investigation demonstrates that other particles instruments onboard Cassini detected an electron burst correlated with this airglow. Modeling of this event brings information on the aerosols distribution in the Titan’s upper atmosphere, on the airglow characteristics and the possible energy sources.