For the first time ever, scientists have detected molecular nitrogen on a comet. The discovery is sheds light on the nature of the pre-Solar System environment in which Comet 67P/C-G formed.

Top photo: Comet 67P/C-G on 14 March 2015 (ESA)

Prior to this discovery, nitrogen had only ever been detected bound up in other compounds, like hydrogen cyanide and ammonia. That said, this new discovery was anticipated by ESA scientists; molecular nitrogen is believed to have been in great abundance when the Solar System was in its formative stage. In the far-away regions of the Solar System, molecular nitrogen likely provided the main source of the element for the gas planets. It's also present in the atmospheres of Pluto, Titan, and Triton.

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And importantly, its presence in the cold outer reaches of the Solar System should have had an influence on the formation of comets like 67P/C-G.

Confirmation of molecular nitrogen on the comet was made by analyzing 138 measurements made by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis instrument, ROSINA. The measurements were captured late last year when the Rosetta probe was about 6.2 miles (10 km) from the comet's center.

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The presence of molecular nitrogen means the comet must have formed under some very specific conditions. Some very cold conditions, that is.

For these molecules to become trapped in the ice, temperatures must have dipped as low as -220ºC and possibly even as low as –250ºC. Similar conditions are required to trap carbon monoxide, which is why the scientists compared the ratios of both. In the case of Comet 67P/C-G, the ratio was 25 times lower than than what was expected. The depletion of these molecules, argue the researchers, may be a result of the ice forming at the exceptionally low temperatures found in the protosolar nebula. These findings suggest Jupiter-family comets were not the primary source of nitrogen for Earth's atmosphere.

[ ESA ]

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