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

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)
https://arxiv.org/abs/1911.13005
Astrobiology, Astrochemistry