Cometary Science Newsletter

Neutral–neutral synthesis of organic molecules in cometary comae

• Cordiner, M. A. ^1,2
• Charnley, S. B. ¹

1. Astrochemistry Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
2. Department of Physics, Catholic University of America, Washington, DC 20064, USA

Remote and in-situ observations of cometary gases have revealed the presence of a wealth of complex organic molecules, including carbon chains, alcohols, imines and the amino acid glycine. Such chemical complexity in cometary material implies that impacts by comets could have supplied reagents for prebiotic chemistry to young planetary surfaces. However, the assumption that some of the molecules observed in cometary comae at millimetre wavelengths originate from ices stored inside the nucleus has not yet been proven. In fact, the comae of moderately-active comets reach sufficient densities within a few thousand kilometers of the nucleus for an active (solar radiation-driven) photochemistry to ensue. Here we present results from our latest chemical-hydrodynamic models incorporating an updated reaction network, and show that the commonly-observed HC3N (cyanoacetylene) and NH2CHO (formamide) molecules can be efficiently produced in cometary comae as a result of two-body, neutral-neutral, gas-phase reactions involving well-known coma species. In the presence of a near-nucleus distributed source of CN (similar to that observed by the Rosetta spacecraft at comet 67P), we find that sufficient HC3N and NH2CHO can be synthesized to match the abundances of these molecules previously observed in Oort cloud comets. The precise coma origins of these (and other) complex organic molecules can be verified through radio interferometric mapping, for example, using the Atacama Large Millimeter/submillimeter Array (ALMA).

MNRAS (Published)

DOI: 10.1093/mnras/stab1123 NASA ADS: 2021MNRAS.504.5401C arXiv: 2104.07577