Research Highlight

How complex molecules form in a comet’s icy core

doi:10.1038/nindia.2016.84 Published online 30 June 2016

By simulating the frigid conditions of a comet’s nucleus, researchers have gained new insights into how heat can convert an ice mixture of carbon disulfide and ammonia into a complex molecule inside a periodic comet1.

Ammonia and carbon disulfide are widely present in many planetary bodies, including comets. These compounds are of great interest to planetary scientists since they could provide vital clues about the role of comets in seeding life on Earth-like planets.

Comets’ icy cores are known to harbour a wide variety of molecules. When exposed to radiation and heat, these molecules undergo phase changes and react with each other, forming complex prebiotic molecules.

To better understand this process, the researchers cooled carbon disulfide and ammonia to −263 degrees Celsius on a substrate in a vacuum chamber. When they warmed this ice mixture of carbon disulfide and ammonia, a residue of a compound was left on the substrate. The signal of this compound was detected in spectra recorded at 67 degrees Celsius. The compound is believed to be ammonium dithiocarbamate, a thio compound.

The chances of forming such thio molecules increase as a comet approaches the Sun, suggesting that periodic comets could be good candidates to look for complex molecules such as ammonium dithiocarbamate, the researchers say.


1. Methikkalam, R. R. J. et al. Thio residue from thermal processing of cometary ices containing carbon disulfide and ammonia. Adv. Space Res. 58, 438–443 (2016)