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Comets are a rich reservoir of complex organic molecules. Ground-basedobservatories like ALMA and in situ measurements such as by the Rosettaenhanced their inventory. Most of these detections occur in the cometaryatmosphere or coma, but their origin is believed to be the cometary nucleus;however, they can be partially synthesised in the coma. We studied organicmolecules' nucleus versus coma origins for a variety of initial conditions,using a multifluid chemical-hydrodynamical model, updated chemical network andemploying a large number of model runs. We considered four Oort cloud comets,namely C/1996 B2 (Hyakutake), C/2012 F6 (Lemmon), C/2013 R1 (Lovejoy), andC/2014 Q2 (Lovejoy) for the study and emphasised the C-H-O and N-bearingspecies, including the simplest amino acid glycine. We discussed theirformation/destruction pathways extensively and the conditions for theirformation in the coma, and found that the abundance varies from one comet tothe other due to differences in the initial conditions, relative abundances ofthe reactants and temperature. We compared between their abundance when theyare present as parent volatile and formed solely due to the gas-phase chemistrywithout them being parent volatiles. We found that production rates of someorganic molecules can be in the range between 1.0e22 and 1.0e26 molecules/s,which is in the realm of detection via in situ/space-based observations.Finally, we compared the model abundances with those observed in 67P/C-G byRosetta, which detected a large number of organics at a large heliocentricdistance and low production rate.

Gas-phase Formation of Organic Molecules in the Comae of Four Oort Cloud Comets