IRTF Data Archive Program Information

# # Program information file # PROGRAM_ID 2021B001 PROGRAM_TITLE Investigating the possible presence of NH3-bearing species on the Uranian satellites and the composition and structure of their regoliths [part 2] PROGRAM_INV1 Richard Cartwright PROGRAM_INV2 Will Grundy PROGRAM_INV3 Bryan Holler PROGRAM_INV4 Tom Nordheim PROGRAM_INV5 Michael Lucas PROGRAM_SCICAT solar system PROGRAM_ABSTRACT_BEG We propose to use the SpeX spectrograph on NASA's Infrared Telescope Facility on selected nights to investigate the possible presence of NH3-bearing species on the Uranian satellites and constrain the composition and structure of their regoliths. NH3-bearing constituents are efficient anti-freezes when mixed with liquid H2O, and they should be effectively removed by charged particles when exposed on the surfaces of the large Uranian moons. Consequently, the possible presence of NH3-rich deposits on the Uranian moons hints at recent exposure of this volatile by geologic processes. Furthermore, the spectral properties of the Uranian moons show clear dissimilarities when comparing shorter wavelength spectra [0.7 - 2.5 microns] to longer wavelength datasets [3 - 5 microns], suggesting that these moons' regoliths are compositionally stratified. The SXD mode of SpeX [R ~750, 0.8'' slit] is ideal for the characterization of the 2.2-micron band. Previously detected 2.2-micron bands are relatively wide [0.03 - 0.05 microns across], requiring R of > 140 to detect. Because the shape and central wavelength of these possible NH3-rich features are poorly constrained, SXD mode [R > 500] is ideal to more precisely characterize these bands. SpeX in LXD_short mode [R ~937, 0.8'' slit] is ideal for characterizing the spectral continuum between 3 and 4 microns, in particular the 3.6-micron H2O ice peak, which is enhanced on the Uranian moons compared to icy satellites elsewhere. Previous analysis of the 3.6-micron H2O ice peak demonstrates that this region is about 0.4 microns across [3.4 to 3.8 microns], requiring R of 18 to detect, which SpeX can readily achieve. To improve the quality of collected LXD_short spectra, we will bin these data by a factor of 50, thereby improving the S/N of collected spectra while maintaining R > 18. We will guide using MORIS [0.7'' dichroic] thereby mitigating slit losses. PROGRAM_ABSTRACT_END