# # Program information file # PROGRAM_ID 2024A070 PROGRAM_TITLE Production and Spatial Distribution of Parent Volatiles in Dynamically New Comet 2021 S3 [PanSTARRS]: Comparison with Astrochemical Disk Midplane Models PROGRAM_INV1 Michael DiSanti PROGRAM_INV2 Erika Gibb PROGRAM_INV3 Boncho Bonev PROGRAM_INV4 Neil Dello Russo PROGRAM_INV5 Ron Vervack PROGRAM_SCICAT comets PROGRAM_ABSTRACT_BEG We propose using iSHELL to measure a suite of parent volatiles [sublimed native ices] post-perihelion in dynamically new comet 2021 S3 [PanSTARRS], targeting H2O, HCN, C2H2, NH3, CH4, C2H6, CH3OH, H2CO, CO, and OCS. This dynamical class of comets incorporates the least processed remnant volatile material from solar system formation. As such, measuring production rates and relative abundances [or establishing meaningful upper limits] for native ices in comet S3 provides the most direct link for comparisons with astrochemical model predictions of the cold, opaque proto planetary disk [PPD] midplane environment. Establishing accurate production rates for individual parent molecules requires knowledge of the spatial distributions [spatial profiles] of their emissions in the coma. At a minimum we will measure spatial profiles for the four species having the brightest emissions: H2O, HCN, C2H6, and CH3OH. For species having weaker emissions, if needed assumptions will be made based on their measurement within the same iSHELL setting: C2H2 and NH3 co-measured with H2O and HCN, H2CO and CH4 with C2H6 and CH3OH, and CO and OCS with H2O. Assessing emission spatial profiles can also reveal differences among species, for example a-polar versus polar ices. We plan multiple measurements spanning days [diurnal measurements] to weeks or more [serial measurements]. Both cadences have the potential to reveal distinct compositions and/or outflow morphologies among active regions of the nucleus. Measured cometary ice compositions will be compared with modeled disk midplane chemical evolution, incorporating large-scale transport processes in the disk and/or heritage from the proto-solar cloud to assess the extent to which primordial signatures are preserved in comets. PROGRAM_ABSTRACT_END