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 H+ 15 3 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 ( λ ∆λ ∼100,000), offers unprecedented spectrally resolved views of Saturn’s infrared aurora. Discrete H+3 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 localised 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−1 , resembling an ionospheric polar vortex. A temperature hotspot of 379 (±66) K may be driving an emission region, corresponding to a location where H+3 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.