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CO, CO₂, and H₂O in Comets and Centaurs

Presentation #101.08 in the session Cometary Volatiles.

Published onOct 20, 2022
CO, CO₂, and H₂O in Comets and Centaurs

CO and CO2 are the two dominant carbon-bearing molecules in comae and have major roles in driving activity. Their relative abundances in comae provide strong observational constraints to models of solar system formation and evolution, and comet nuclei behavior, but relative abundances of the detections have never before been studied in a relatively large sample of comets. We compared and analyzed published measurements of simultaneous CO and CO2 production rates for 25 comets. Comparing the relative abundance, CO/CO2, approximately half of the comae have substantially more CO2 than CO, about a third are CO-dominated and about a tenth produce comparable amounts of both gases. There may be a heliocentric dependence to this ratio with CO dominating compared to CO2 beyond 3.5 au. Most (89%) of Jupiter Family Comets have CO2-dominated comae compared to CO, while Oort Cloud Comets show no clear preference. Among 14 Oort Cloud Comets, those on their first trip to the inner solar system (5) have comae which are CO2-dominant compared to CO, while those on subsequent trips tend to be CO-dominant compared to CO2, and a trend may be present with increasing CO produced relative to CO2 with more thermal processing. Within 2.5 au, we find median values of the relative production rates (QA/QB) QCO/QH2O = 3±1% and QCO2 /QH2O = 12±2% and total amount of CO and CO2 produced relative to H2O is near 20% with little variation across our sample. Between 0.7 to 4.6 au, CO2 outgassing appears to be more intimately tied to the water production in a way that the CO clearly is not. We estimate carbon/oxygen ratios for the volatile components within 2.5 au and find a median value of C/O = 13%.

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