# # Program information file # PROGRAM_ID 2022B038 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 major planets / satellites 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 ~6500 for the 2022 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 would extend documentation of Uranus' seasonal response in anticipation of an imminent seasonal trend reversal, which would reveal the dissipative time constant for thermospheric seasonal change, and hence provide information on the unknown heating process. Averaging the nightly observations would help to smooth out the longitudinal variation of the temperature for a closer comparison to the established temperature downtrend line, and so to an earlier detection of the trend reversal. PROGRAM_ABSTRACT_END