Evidence of Ammonium Salts In Comet 67P As Explanation For The Nitrogen Depletion In Cometary Comae

Abundance ratios for the period around 20h compared to 17h UTC on Sept. 5, 2016. For species not detected before impact, upper limits were derived from the noise floor of the detector, which translates into lower limits for the ratios. Sublimation of ammonium salts may produce water, CO and CO2. Their contributions to these species are small as these are the dominant species of the undisturbed coma. We consider them “uncorrelated” to ammonium salt.

Cometary comae are generally depleted in nitrogen. The main carriers for volatile nitrogen in comets are NH3 and HCN. It is known that ammonia readily combines with many acids like e.g. HCN, HNCO, HCOOH, etc. encountered in the interstellar medium as well as in cometary ice to form ammonium salts (NH4+X-) at low temperatures.

Ammonium salts, which can play a significant role in prebiotic chemistry, are hard to detect in space as they are unstable in the gas phase and their infrared signature is often hidden by thermal radiation or by e.g. OH in minerals. Here we report the presence of all possible sublimation products of five different ammonium salts at comet 67P/Churyumov-Gerasimenko measured by the ROSINA instrument on Rosetta.

The relatively high sublimation temperatures of the salts leads to an apparent lack of volatile nitrogen in the coma. This then also explains the observed trend of higher NH3/H2O ratios with decreasing perihelion distances in comets.

K. Altwegg, H. Balsiger, J.-J. Berthelier, C. Briois, M. Combi, H. Cottin, J. De Keyser, F. Dhooghe, B. Fiethe, S. A. Fuselier, T. I. Gombosi, N. Hänni, M. Rubin, M. Schuhmann, I. Schroeder, T. Sémon, S. Wampfler
(Submitted on 29 Nov 2019)

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1911.13005 [astro-ph.EP] (or arXiv:1911.13005v1 [astro-ph.EP] for this version)
Submission history
From: Kathrin Altwegg
[v1] Fri, 29 Nov 2019 09:07:22 UTC (2,350 KB)
Astrobiology, Astrochemistry

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