Tag Archives: organic compounds

Rosetta finds carbon molecules in comet dust

The Rosetta science team has announced that they have detected very complex carbon molecules in solid dust particles that were released from Comet 67P/C-G.

“Our analysis reveals carbon in a far more complex form than expected,” remarked Hervé Cottin, one of the authors of the paper reporting the result that is published in Nature today. “It is so complex, we can’t give it a proper formula or a name!” The organic signatures of seven particles are presented in the paper, which the COSIMA team say are representative of the two hundred plus grains analysed so far.

The carbon is found to be mixed with other previously reported elements such as sodium, magnesium, aluminium, silicon, calcium and iron. It is bound in very large macromolecular compounds similar to the insoluble organic matter found in carbonaceous chondrite meteorites that have fallen to Earth, but with a major difference: there is much more hydrogen found in the comet’s samples than in meteorites.

But as this kind of meteorite is associated with reasonably well-processed parent bodies such as asteroids, it is reasonable to assume that they lost their hydrogen due to heating. By contrast, comets must have avoided such significant heating to retain their hydrogen, and therefore must contain more primitive material.

Because of the use of the term organics here for these carbon-based molecules, expect a lot of news reports to misreport this discovery and incorrectly announce with great excitement that Rosetta has “discovered life” on Comet 67P/C-G! Among scientists, any carbon molecule is referred to as organic, even if it is entirely inanimate. In this case these molecules are not the result of life, but of carbon’s atomic structure, allowing it to form an infinite variety of molecules with almost any other element.

Rosetta finds organic compounds at Comet 67P/C-G

Rosetta’s scientists have detected the amino acid glycine as well as other organic molecules in the atmosphere of Comet 67P/C-G.

Glycine is very hard to detect due to its non-reactive nature: it sublimates at slightly below 150°C, meaning that little is released as gas from the comet’s surface or subsurface due to its cold temperatures. “We see a strong correlation of glycine to dust, suggesting that it is probably released from the grains’ icy mantles once they have warmed up in the coma, perhaps together with other volatiles,” says Altwegg. At the same time, the researchers also detected the organic molecules methylamine and ethylamine, which are precursors to forming glycine. Unlike other amino acids, glycine is the only one that has been shown to be able to form without liquid water. “The simultaneous presence of methylamine and ethylamine, and the correlation between dust and glycine, also hints at how the glycine was formed”, says Altwegg.