# # Program information file # PROGRAM_ID 2022A055 PROGRAM_TITLE Investigation of CO vs H2O driven outgassing in comet C/2017 K2 [PanSTARRS] PROGRAM_INV1 Chemeda Ejeta PROGRAM_INV2 Erika Gibb PROGRAM_INV3 Nathan Roth PROGRAM_INV4 Neil Dello Russo PROGRAM_INV5 Younas Khan PROGRAM_SCICAT comets PROGRAM_ABSTRACT_BEG We propose using the iSHELL instrument to measure the hypervolatile composition of the Oort cloud comet C/2017 K2 [PanSTARRS] [hereafter K2] during the upcoming semester at large Rh [~3.2 - 2.9 au]. At large heliocentric distances [beyond about 3 au], comet activity is primarily driven by the sublimation of more volatile molecules, including CO, CH4, C2H6, and CO2. By the time comets reach 2 au, water is fully activated and drives volatile release. However, there are very few observations of volatile release in the critical region near 2.5-3 au, where water sublimation should transition to the dominant source of activity. Observations of the parent volatiles in comets at these heliocentric distances are therefore crucial to fully understand the evolution of coma composition and outgassing as comets transition from CO-dominated to H2O-dominated activity. We propose to observe K2 in May-June 2022 as it approaches its first perihelion to investigate how hypervolatile abundances evolve every ~0.1 au over this critical region to test if and how water sublimation turns on over this range of heliocentric distance. Given that K2 is one of the few [dynamically new] comets in which molecular activity can be traced at these heliocentric distances, the proposed observations of K2 offer a unique opportunity to sample volatile composition near the H2O ice-line and characterize the interplay between the gases driving activity in this less-explored transition region. In addition, we will measure or significantly constrain H2O, CH3OH, and H2CO and investigate how the volatile composition of K2 evolves with heliocentric distance. PROGRAM_ABSTRACT_END