Presentation #411.11 in the session Cometary Volatiles (iPosters).
Formed during the era of planet formation, comets are some of the most primitive remnants of the solar system. Remaining relatively unaltered since their formation, characterizing the composition of comet comae (and by inference, their nucleus ices) provides us with a glimpse into the thermal and chemical processes present in the early stages of solar system formation. Intriguing trends have been found in the few comets studied at small heliocentric distances (< 0.8 au), including increased molecular abundances and production from distributed sources. This study investigates the evolution of molecular production in disrupting Oort cloud comet D/2021 A1 (Leonard)—the subject of multi-wavelength observing campaigns owing to its small perihelion distance (0.61 au) and close approach to Earth (0.23 au) during its 2021 perihelion passage. We report pre-perihelion observations of D/2021 A1 using the Northern Extended Millimeter Array (NOEMA) and the Atacama Pathfinder EXperiment (APEX) on multiple dates in 2021 November and December. We sampled molecular emission from HCN, CS, H2CO, CO, and CH3OH with both facilities, monitoring their evolution from heliocentric distances of 1.31 au to 0.79 au as comet D/2021 A1 approached the Sun. We report molecular production rates, mixing ratios (relative to H2O), spectrally integrated interferometric maps, single-dish spectra, and place our results into context with other comets measured at similar heliocentric distances through comparison with contemporaneous IR measurements of relevant molecular species at Keck and the IRTF. This work is based on observations carried out under project number S21AA with the IRAM NOEMA Interferometer, and on observations with the Atacama Pathfinder EXperiment (APEX) telescope carried out under project number O-0108.F-9322A-2021. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). APEX is a collaboration between the Max Planck Institute for Radio Astronomy, the European Southern Observatory, and the Onsala Space Observatory. Swedish observations on APEX are supported through Swedish Research Council grant No 2017-00648.