# # Program information file # PROGRAM_ID 2024B004 PROGRAM_TITLE Determining the origin and nature of the 4.57-micron band on Callisto and Ganymede: A possible tracer of nitrogen or sulfur chemistry in the Jupiter system PROGRAM_INV1 Richard Cartwright PROGRAM_INV2 Chloe Beddingfield PROGRAM_INV3 Katherine de Kleer PROGRAM_INV4 Kevin Hand PROGRAM_INV5 Carl Schmidt PROGRAM_SCICAT major planets / satellites PROGRAM_ABSTRACT_BEG We propose to use SpeX on IRTF to measure the distribution and spectral signature of a 4.57-micron absorption feature on the icy Galilean moons Ganymede and Callisto. The 4.57-um band was originally attributed to CN-bearing species that are possibly native to these moons or delivered in dust grains. Because of the low resolving power of the NIMS spectrometer [R ~200] onboard Galileo. and the generally low S/N of NIMS spectra at wavelengths > 4.3 microns, the 4.57-micron band has been difficult to assess using spacecraft data. The longitudinal distribution and band morphology of this feature has been partly mapped using SpeX, but its spectral properties are not well constrained on Callisto's anti-Jovian and sub-Jovian hemispheres. Furthermore, both NIMS and SpeX detected a weak 4.57-micron feature on Ganymede's anti-Jovian side, but its presence is still unconfirmed and spectral mapping of its longitudinal distribution has yet to be completed. Our proposed 2024B observations will fill existing gaps in SpeX coverage and provide key data for unraveling the surface chemistry of the Galilean moons, thereby providing useful preparatory science for the upcoming NASA Europa Clipper and ESA JUICE missions to the Jovian system. SpeX in LXD_long mode [~2.0 - 5.3 microns, 0.3' slit] is ideal for detecting and characterizing the 4.57-micron band, with sufficient resolving power [R ~2500] to characterize the morphology of this feature. Using the online SpeX Observation Calculator, we estimate that we can achieve sufficient signal-to-noise to achieve our project goals in 4800 s for the H2O-rich surface of Ganymede [Vmag ~5.0, considerably darker in M band], and 3600 s for Callisto [Vmag ~6.0]. We will use the near-infrared guider [Guidedog]. PROGRAM_ABSTRACT_END