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Comets are a rich reservoir of complex organic molecules. Ground andspace-based observatories have recently greatly enhanced the cometary molecularinventory. Although these molecules' origin is believed to be the cometarynucleus, they can be partially synthesised in the coma. We studied organicmolecules' nucleus versus coma origins for various initial conditions, using amultifluid chemical-hydrodynamical model and an updated chemical network. Forthe study, we considered four comets [C/1996 B2 (Hyakutake), C/2012 F6(Lemmon), C/2013 R1 (Lovejoy), and C/2014 Q2 (Lovejoy)] due to their relativelyhigh activity and observation of large number organics species. We emphasisedon the C-H-O and N-bearing species, including the simplest amino acid, glycine.We discuss the formation pathways of the organics and the conditions for theirformation in the coma and find that the abundance varies from one comet toanother due to differences in the initial conditions, relative abundances ofthe reactants and temperature. We compare the organic abundances when they arepresent as parent volatiles to their formation solely due to gas-phasechemistry. Their abundance purely due to the coma chemistry is moderately tosignificantly lower compared to that when they are parent volatiles. However,we find that the production rates of some of the coma-synthesised organicmolecules can reach peak values of ~ 1e22 - 1e26 molecules/s, which is in therealm of detection by in situ/space-based observations, and can therefore beimportant considering future missions to comets. We also compare our modeledabundances with those observed in 67P/C-G by Rosetta, which detected severalorganics at a large heliocentric distance and low production rate.

The extent of formation of organic molecules in the comae of comets showing relatively high activity