# # Program information file # PROGRAM_ID 2021B109 PROGRAM_TITLE iSHELL Observations of Uranus' K-band H2 Emission Spectrum PROGRAM_INV1 Laurence Trafton PROGRAM_INV2 Henrik Melin PROGRAM_INV3 PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT solar system PROGRAM_ABSTRACT_BEG We propose to use iSHELL with the K3 setting at the IRTF to observe Uranus' whole-disk, K-band, H2 Q-branch emission spectrum through the 4' slit at R= 9000 for the 2021 apparition. The spectrum will be analyzed to extract the rotational temperature of H2 in Uranus' thermosphere, which has been declining for longer than the planet's 21-yr season. This is needed to understand the excess heating and energy balance of Uranus' upper atmosphere, which cannot be explained by solar EUV heating alone. This is part of a program of monitoring its long-term cooling in anticipation of a seasonal trend reversal, which would reveal the dissipative time constant for thermospheric seasonal change, and hence provide information on the unknown heating process. The observations will average all longitudes visible over a full rotation, helping to average out the longitudinal variation of the temperature for comparison to the established temperature downtrend line. PROGRAM_ABSTRACT_END