Comets may have sparked life on Earth: study

Scientists have discovered key components of DNA and cell membranes including the simple amino acid glycine and phosphorus on a comet for the first time, suggesting that such cosmic bodies may have brought these crucial ingredients for life on Earth.

The possibility that water and organic molecules were brought to the early Earth through impacts of objects like asteroids and comets have long been the subject of debate.

The space probe Rosetta, built by the European Space Agency, along with its lander module Philae, is performing a detailed study of comet 67P/Churyumov Gerasimenko.

While Rosetta’s ROSINA instrument already showed a significant difference in composition between Comet 67P/C-G’s water and that of Earth, researchers from University of Bern in Switzerland found that even if comets did not play a big role in delivering water as once thought, they certainly had the potential to deliver life’s ingredients.

While more than 140 different molecules have already been identified in the interstellar medium, amino acids could not be traced.

However, hints of the amino acid glycine, a biologically important organic compound commonly found in proteins, were found during NASA’s Stardust mission that flew by Comet Wild 2 in 2004, but terrestrial contamination of the collected dust samples during the analysis could not be ruled out.

Now, for the first time, repeated detections at a comet have been confirmed by Rosetta in Comet 67P/C-G’s fuzzy atmosphere, or coma.

The first detection was made in October 2014, while most measurements were taken in August last year during the perihelion - the closest point to the Sun along the comet’s orbit while the out-gassing was strongest.

“This is the first unambiguous detection of glycine in the thin atmosphere of a comet,” said Kathrin Altwegg, principal investigator of the ROSINA instrument at the University of Bern.

Glycine is very hard to detect due to its non-reactive nature: it sublimates at slightly below 150 degrees Celsius, 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,” said 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,” said Altwegg.

ROSINA also detected phosphorus for the first time at a comet. It is a key element in all living organisms and is found in the structural framework of DNA and RNA. The research appears in the journal Science.