# # Program information file # PROGRAM_ID 2023B059 PROGRAM_TITLE Io's atmosphere following perihelion PROGRAM_INV1 John Spencer PROGRAM_INV2 Rohini Giles PROGRAM_INV3 Thomas Greathouse PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT major planets / satellites PROGRAM_ABSTRACT_BEG We will use TEXES to measure the temporal and longitudinal variability of Io's atmosphere, using SO2 bands near 19 um. The data will extend a 20-year record of the spatial inhomogeneities and seasonal variation of the atmosphere. A sharp peak in atmospheric density was seen near perihelion on both the Jupiter-facing and anti-Jupiter hemispheres in 2011, providing strong evidence for sublimation support, and was seen again approaching the next perihelion in 2022, clinching the argument for sublimation support. We plan to monitor atmospheric response shortly after the early 2023 perihelion to better determine the shape of the perihelion peak to constrain frost thermal properties, including on the Jupiter-facing hemisphere. We will also look for spikes due to discrete volcanic events, and establish a record of atmospheric variability to support the two Juno close flybys of Io, one of which occurs during this semester. We are requesting eight 3-hour observing periods during this semester to measure Io's atmospheric density at up to eight longitudes, to improve on recent temporal and longitudinal coverage. We will ratio our Io spectra to Callisto spectra to remove telluric and instrumental signatures from the data. SNR of 250 is expected given the known brightness of Io for the proposed integration times, sufficient to retrieve the SO2 column abundance to within 10%. PROGRAM_ABSTRACT_END