# # Program information file # PROGRAM_ID 2023B013 PROGRAM_TITLE Observations of Uranus' Near-IR 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 arcsec slit at R ~6500 for the 2023 apparition. The spectrum will be analyzed to extract the disk-averaged rotational temperature of H2, which has been declining for well longer than the planet's season. These observations are needed to understand the energy balance of Uranus' upper atmosphere, particularly the source of its excess heating, which cannot be explained by solar EUV insolation alone. These observations are also needed to extend the time series documenting Uranus' seasonal response to solar forcing in anticipation of a potentially imminent seasonal temperature trend reversal. Establishing the epoch of this reversal would reveal the dissipative time constant for the response of the thermosphere to seasonal forcing, which should help to constrain the unknown heating process. The excited H2 column abundance will also be extracted, which will be useful for establishing the cooling rate of Uranus' thermosphere -- further constraining the unknown heating source there. Finally, the spectral images of Uranus' disk will be searched for localized auroral heating of H2 and the results compared to the extracted disk-averaged temperatures in an attempt to assess the importance of auroral heating as a potential source of the unexplained high themospheric temperatures. PROGRAM_ABSTRACT_END