# # Program information file # PROGRAM_ID 2022A043 PROGRAM_TITLE The exceptional passage of comet C/2021 O3 [Pan-STARRS ]: investigations of its volatile and isotopic composition at near-IR wavelengths. PROGRAM_INV1 Michael Mumma PROGRAM_INV2 Sara Faggi PROGRAM_INV3 Geronimo Villanueva PROGRAM_INV4 Manuela Lippi PROGRAM_INV5 PROGRAM_SCICAT comets PROGRAM_ABSTRACT_BEG We propose to investigate primary volatiles, ammoniated salts, and the water isotopic ratio in comet C/2021 O3 [Pan-STARRS] as it exits perihelion at heliocentric distances of about 0.5 -- 0.7 au. Ammoniated salts can be produced at 10-15 K and they will survive until ~200K and higher, meaning that salts now present in cometary nuclei could have formed in the natal interstellar cloud core. Once ejected by a comet, especially at very small Rh, salts can be heated to dissociation temperatures by solar radiation and dissociate into their constituent species [HCN, NH3, ...]. The formation of HDO is strongly temperature dependent and measured isotopic ratios in comets are beginning to comprise a statistically significant sample. Early results for D/H suggested that most comets are consistent with about twice the value in Earth's oceans however recent improvements in instrumental sensitivities have enabled HDO measurements in moderately bright comets with the result that the known abundance of HDO relative to H2O now varies among both Jupiter Family and Oort Cloud [OC] comets. The exceptional passage of comet O3 and its favorable visibility and extremely high Figure-of-Merit in early May make this object a unique and timely target for these isotopic and semi-volatile investigations. To obtain a complete characterization of the outgassing activity/variability, and its molecular and isotopic composition we propose to follow comet O3 as closely as possible, on 4 days while it exits from the perihelion. We will target the nitrile region [especially HCN, NH3, NH2 and H2O] in L1-c [2.9 to 3.1 um]; the carbon-stretch region [targeting CH4, C2H6, CH3OH, H2CO, HDO and OH*] in Lp1-c [3.3-3.7 um]; and CO, CN, OCS and H2O in M1 [4.5 to 5.2 um]. In doing so, we will characterize the comet's chemical composition and test the origin of its material. PROGRAM_ABSTRACT_END