Exploring Key Characteristics in Saturn's Infrared Auroral Emissions Using VLT-CRIRES: H3+ Intensities, Ion Line-of-Sight Velocities, and Rotational Temperatures

We present a study of Saturn's (Formula presented.) northern auroral emission using data from 19 May 2013 from the Very Large Telescope's long-slit spectrometer Cryogenic Infrared Echelle Spectrograph (VLT-CRIRES). Adaptive optics, combined with the spectral resolution of VLT-CRIRES ((Formula presented.) 100,000), offers unprecedented spectrally resolved views of Saturn's infrared aurora. Discrete H3+ emission lines—used to derive dawn-to-dusk profiles of auroral intensity, ion line-of-sight velocity, and thermospheric temperature—reveal a dawn-enhanced aurora with an average temperature of 361 (±48) K and a localized dark region in the emission co-located with a noon-to-midnight (and vice versa) flow in the ion velocity on the scale of ∼1 km/s, resembling an ionospheric polar vortex. A temperature hotspot of 379 (±66) K may be driving an emission region, corresponding to a location where (Formula presented.) is failing to cool the thermosphere. Results presented here have implications for current understanding on the complex nature of Saturn's thermosphere-ionosphere-magnetosphere interaction.