Program: GN-2020B-Q-219

Gemini/GNIRS will observe Uranus in the K- and L-bands to obtain near-IR emission spectra of H3+ and H2 at medium spectral resolution during the 2020 apparition. The multiple rotational levels observed by GNIRS in each band will permit the extraction of the ro-vib temperature of Uranus' neutral thermosphere and ionosphere, respectively, for the current seasonal phase. The results will help to update a continuing seasonal record showing secular downtrends in the temperature for both species, which has now lagged over half a season past the 2007 spring equinox, when solar forcing should begin to heat the more-illuminated hemisphere. A seasonal reversal in the temperature has long been anticipated and these data will help to characterize either a seasonal reversal itself or a continuing downtrend. Separate epochs of the reversals are expected that should reveal characteristic seasonal response times for the thermosphere and ionosphere, respectively. These would bear on the role of dynamics in the seasonally changing energy balance of Uranus’ upper atmosphere. The results may be relevant to understanding the unknown source of Uranus' high thermospheric temperature, an open question since the Voyager epoch.