IRTF Data Archive Program Information

# # Program information file # PROGRAM_ID 2022A025 PROGRAM_TITLE Investigating the composition of dark material on the Saturnian moons Tethys, Dione, Rhea, and Iapetus: Rich in ammonia and organics? PROGRAM_INV1 Richard Cartwright PROGRAM_INV2 Chloe Beddingfield PROGRAM_INV3 Tom Nordheim PROGRAM_INV4 Francesca Scipioni PROGRAM_INV5 Joshua Emery PROGRAM_SCICAT major planets / satellites PROGRAM_ABSTRACT_BEG We propose to collect SpeX spectra of the Saturnian moons Tethys, Dione, Rhea, and Iapetus to investigate whether the dark material observed on their surfaces is rich in [NH3] and organics. Prior ground-based observations have detected a subtle 2.2-micron band on Tethys and Rhea, which was tentatively attributed to NH3-bearing species. Similarly, observations made be the Visual and Near Infrared Mapping Spectrometer [VIMS] on Cassini detected a 2.97-micron band in dark regions on Dione and Iapetus that was attributed to NH3 as well. However, the 2.97-micron feature falls near an order-sorting filter and is difficult to verify, and VIMS did not detect a 2.2-micron band on any of Saturn's moons. More recent SpeX observations have confirmed the presence of a subtle 2.21-micron band on these moons. This feature appears to be stronger at sub-observer longitudes covering dark regions on these moons. Similarly, SpeX detected a subtle 2.39-micron band, which also appears to be stronger at longitudes corresponding to low albedo regions. The composition of the 2.39-micron band is unknown, but organic-rich clathrates may represent plausible contributors to this feature. SpeX in SXD mode [0.8' slit, R ~750] is ideal for measuring the 2.21-micron and 2.39-micron bands on Saturn's moons. These bands are ~0.012 and 0.01 microns wide, requiring a minimum R of ~552 and ~716, respectively, to place at least three points along each band. The continuum-divided band depths for the 2.21-micron and 2.39-micron features are 0.4 -- 1.5% and 1 -- 3%, requiring signal-to-noise ratios [SNR] >= 250 and 100, respectively, to detect them. The SpeX online calculator estimates that integration times of 20 min. [Tethys and Dione], 15 min. [Rhea], 35 min. [Iapetus, trailing hemisphere], and 60 min. [Iapetus, leading hemisphere] are required to meet our SNR requirements. Overheads roughly double these integrations times in SXD mode. PROGRAM_ABSTRACT_END