# # Program information file # PROGRAM_ID 2022A024 PROGRAM_TITLE Unraveling the carbon, nitrogen, and sulfur chemical systems operating on the Galilean moons Ganymede and Callisto: What species and processes form the 4.6-micron band? PROGRAM_INV1 Richard Cartwright PROGRAM_INV2 Tom Nordheim PROGRAM_INV3 Kevin Hand PROGRAM_INV4 Joshua Emery PROGRAM_INV5 Joe Roser PROGRAM_SCICAT major planets / satellites PROGRAM_ABSTRACT_BEG We propose to use SpeX on IRTF to measure the distribution and spectral signature of a 4.6-micron absorption feature on the Galilean moons Ganymede and Callisto, discovered by the Near Infrared Mapping Spectrometer [NIMS] onboard the Galileo spacecraft. The 4.6-um band was originally attributed to CN-bearing species that are possibly native to these moons. However, because of the low resolving power of NIMS [R 40 - 200] and generally low S/N of NIMS spectra at wavelengths > 4.3 microns, the 4.6-micron band has been difficult to assess using NIMS data. The spatial distribution of this feature is not well constrained, and it is still uncertain whether it is stronger on these two moons' leading or trailing hemispheres or perhaps is concentrated in specific geologic regions like the Valhalla and Asgard impact basins on Callisto. Furthermore, other species like carbon suboxide [C3O2] and carbon disulfide [CS2] have been suggested as the primary contributors to the 4.6-micron band, and perhaps CN-bearing species [i.e., nitriles] are not present at all on these two moons. Thus, these proposed observations will provide key data for unraveling the carbon, nitrogen, and sulfur chemical systems operating on Ganymede and Callisto. SpeX in LXD_long mode [~2.0 - 5.3 microns, 0.3' slit] is ideal for detecting and characterizing the 4.6-micron band, with sufficient resolving power [R ~2500] to characterize the shape of this feature. Using the online SpeX Observation Calculator, we estimate that in 2800 s of integration time for Ganymede [Vmag 4.8-5.2] and 3600 s of integration time for Callisto [Vmag 5.8-6.2], we can achieve sufficient signal-to-noise to achieve our project goals. To ensure we can observe during twilight, we will use the near-infrared guider, Guidedog. PROGRAM_ABSTRACT_END