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Comet probe detects the «most wanted molecule»

Science MagazineMarch 20, 2015 - ESA’s comet probe Rosetta has for the first time ever measured nitrogen gas at a comet, providing clues to the early stages of the formation of our solar system.

The measurement was made possible thanks to the high mass resolution of the ROSINA/DFMS mass spectrometer, for which the Royal Belgian Institute for Space Aeronomy together with imec and OIP built most of the detector assembly.

The study was led by researchers at the University of Bern and has now been published in the journal «Science».

Molecular nitrogen, N2, is the major molecule in the atmosphere of Earth and is also present in the atmospheres and the surfaces of Pluto and Neptune’s moon Triton. It also is thought to have been the dominant form of nitrogen in the early nebula from which our solar system emerged.

Martin Rubin from the Physics Institute at the University of Bern and his team were now able to measure this «most wanted molecule», as Rubin calls it, in the coma, the atmosphere, of comet 67P/Churyumov-Gerasimenko. It is for the first time ever that scientists were able to detect nitrogen molecules at a comet. «Although some comets like ‹Chury› were probably formed in the same region as Triton and Pluto, until now we weren’t able to find any molecular nitrogen in them», Rubin explains. «Because a comet’s water ice can trap only small amounts of it, remote sensing as well as in situ analysis were simply not sensitive and precise enough.»

DFMS N2 Rosetta
(A) Background mass per charge spectrum around 28 u/e obtained on May 11, 2014 at 1.65 x 106 km from the comet.
(B) Representative spectrum in the coma of the comet on October 18, 2014, 00:47 UTC at almost 10 km cometocentric distance.


The nitrogen measurements suggest that Chury formed in a very cold region of our solar system. «The amount of molecular nitrogen brought to Earth by comets such as 67P/Churyumov-Gerasimenko is small compared to other nitrogen-bearing molecules», says ROSINA Principal Investigator Kathrin Altwegg. According to her, these results add to the growing evidence that Jupiter-family comets like Chury cannot be the major source of both water and volatiles like nitrogen on Earth.

Science MagazineAltwegg and her team had recently discovered that the ratio of deuterium to hydrogen in the water of the comet differed from that on Earth, which indicated that the latter had a different source. «Like the origin of our water, the missing molecular nitrogen in comets was another open question raised during the Giotto mission to comet 1P/Halley almost 30 years ago», she explains. «It is very satisfying that it can be finally answered now.»

Publication details:

M. Rubin, K. Altwegg, H. Balsiger, A. Bar-Nun, J.-J. Berthelier, A. Bieler, P. Bochsler, C. Briois, U. Calmonte, M. Combi, J. De Keyser, F. Dhooghe, P. Eberhardt, B. Fiethe, S. A. Fuselier, S. Gasc, T. I. Gombosi, K. C. Hansen, M. Hässig, A. Jäckel, E. Kopp, A. Korth, L. Le Roy, U. Mall, B. Marty, O. Mousis, T. Owen, H. Rème, T. Sémon, C.-Y. Tzou, J. H. Waite, P. Wurz, «Molecular nitrogen in comet 67P/Churyumov-Gerasimenko indicates a low formation temperature», Science, 2015


J. De Keyser and F. Dhooghe
Space Physics Division, BIRA-IASB

Read more on the ESA Blog: Rosetta makes first detection of molecular nitrogen at a comet


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