IRTF Data Archive Program Information

# # Program information file # PROGRAM_ID 2022B089 PROGRAM_TITLE Compositional measurements as comet C/2017 K2 [PanSTARRS] transitions from hypervolatile to water dominated activity. PROGRAM_INV1 Chemeda Ejeta PROGRAM_INV2 Erika Gibb PROGRAM_INV3 Mohammed Saki PROGRAM_INV4 Mike DiSanti PROGRAM_INV5 Neil Dello Russo PROGRAM_SCICAT comets PROGRAM_ABSTRACT_BEG We propose using iSHELL to measure the volatile composition of Oort cloud comet [OCC] C/2017 K2 [PanSTARRS; hereafter K2] during the upcoming apparition over a range of heliocentric distances [Rh] between 2.5-2.3 au. At large heliocentric distances [>3 au], comet activity is primarily driven by the sublimation of more volatile molecules, including CO, CH4, C2H6, and CO2. Once a comet is within Rh < 2 au, where most comet primary volatile measurements are performed, comets are thought to have completed the transition from hypervolatile-dominated to H2O-dominated activity. Measurements between Rh = 2-3 au are thus crucial for understanding the evolution of coma composition and outgassing patterns as comets make this transition. Few comets have been observed in the IR between 2.0-2.5 au and those comets have exhibited enriched abundances compared to the general population of OCCs, so exploring this heliocentric distance range is critical for understanding how comet activity evolves. We propose observing K2 in Aug 2022 as it approaches its perihelion. Owing to its favorable observing conditions [brightness, Figure-of-Merit, and geocentric velocity] during the upcoming apparition, many molecules can be detected or their abundances meaningfully constrained. To characterize the overall volatile chemical composition of K2, we will sample multiple emission lines for H2O, CH3OH, HCN, CO, CH4, C2H6, H2CO, C2H2, NH3, and OCS using three iSHELL grating settings. Along with already scheduled iSHELL observations of K2 over Rh=3.2-2.9 au [private comm.], the proposed observations extending Rh to 2.5-2.3 au will provide an important comparison with observations made beyond the canonical 'water ice line' near 3 au. PROGRAM_ABSTRACT_END