# # Program information file # PROGRAM_ID 2021A001 PROGRAM_TITLE Investigating the sulfur, carbon, and nitrogen chemical systems operating on Callisto PROGRAM_INV1 Richard Cartwright PROGRAM_INV2 Tom Nordheim PROGRAM_INV3 Dale Cruikshank PROGRAM_INV4 Kevin Hand PROGRAM_INV5 Joe Roser PROGRAM_SCICAT solar system PROGRAM_ABSTRACT_BEG We propose to collect new SpeX spectra of the icy moon Callisto to investigate the origin and composition of a 4-micron band that was originally detected by the Near Infrared Mapping Spectrometer [NIMS] onboard Galileo. The low resolving power [R ~200] and often low signal-to-noise [S/N] of data collected by NIMS limited prior analyses of this band. Consequently, the 4-micron band has been attributed to both sulfur dioxide and carbonates. Additionally, the origin of this band remains uncertain, and it could result from irregular satellite dust accumulation, radiolysis driven by implantation of S ions, or impact exposure. Other absorption bands detected on Callisto between 2.85 and 5.0 microns are also poorly understood and warrant further investigation. For instance, the 4.6-micron band could result from CN-bearing material delivered as irregular satellite dust. New observations of Callisto, made at complementary longitudes to our prior SpeX observations, are needed to more fully characterize the distributions and spectral signatures of these features. SpeX in LXD_long mode [~2.0 - 5.3 microns, 0.3'' slit, R ~2500] is ideal for detecting and characterizing the 4-micron and 4.6-micron bands and other features between 2.85 and 5.0 microns detected on Callisto. The resolving power we require to characterize a variety of absorption features ranges from R ~60 to 500. Thus, the moderate resolution of LXD_long mode is ideal for this project. In 3600 s of integration time [0.8'' seeing, 0.3'' slit], we can achieve sufficient S/N to achieve our project goals each night. The integration time/observing time ratio is relatively low for LXD_long observations [~0.19], due to many short exposures increasing read out time [3 s exposure limit to avoiding saturation at wavelengths > 4 microns]. Furthermore, we require fairly long observations of solar analog G-type stars to improve the S/N of the resulting spectra. PROGRAM_ABSTRACT_END