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Understanding Phosphorus Chemistry in Cometary Comae

Presentation #322.14 in the session Comets (Poster + Lightning Talk)

Published onOct 23, 2023
Understanding Phosphorus Chemistry in Cometary Comae

Introduction: Phosphorus is a key element in all living organisms but its role in life’s origin is not well understood. Phosphorus-bearing compounds have been observed in small Solar System bodies as well as planets, the ISM, and other space environments. They have been detected in the dust component of comets 1P/Halley and 81P/Wild 2, and as atomic P and PO in the gas phase of 67P/Churyumov-Gerasimenko by the Rosetta Mission.

Results and Discussion: Our gas dynamics model of cometary comae with chemical kinetics has been adapted to study this problem. Cosmic abundances of phosphine (PH3) and phosphorus monoxide (PO) were used as native molecules. More than one hundred photolytic and gas-phase reactions and about three dozen P-bearing species were added to the chemical network. We have identified reaction pathways of gas-phase and photolytic chemistry for simple P-bearing molecules likely to be found in the inner coma. Protonation reactions of PH3 with water-group ions are important due to its high proton affinity. The scale length of PH3 in the coma is about 14,500 km at 1 au from the Sun. Abundances are found to be on the order of 10-4 relative to water, about the same as isotopic species.

Conclusions: We present results from a quantitative study of P-bearing molecules that identifies the relevant phosphorus chemistry in cometary coma. Suggestions to observers using modern telescopic facilities are given to aid in future searches for phosphorus in comets, including likely prebiotic species.

Acknowledgments: This work was supported by FAPESP (Grant No. 2015/03176-8, Brazil), the National Science Foundation Planetary Astronomy Program (Grant No. 0908529, USA), and the MEXT Supported Program for the Strategic Research Foundation at Private Universities, 2014-2018 (Japan).

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