Halogens at Comet 67P/Churyumov-Gerasimenko seen with ROSINA-DFMS

The Rosetta spacecraft has been studying the coma of comet 67P/Churyumov-Gerasimenko since August 2014 and will continue to do so up to the comet's perihelion and for part of the voyage of the comet away from the Sun. The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) sensor DFMS is a double focussing mass spectrometer with a mass range 13-140 u/e. It is optimized for high mass resolution and large dynamic range and is an invaluable tool for the characterization of neutrals in the coma (1). Hydrogen fluoride (HF) and hydrogen chloride (HCl) are expected to be the main reservoirs of fluorine and chlorine wherever hydrogen is predominantly molecular in the interstellar medium (2). The strong depletion of these compounds in dense molecular clouds suggests freeze-out of these compounds onto grains in cold environments (3, 4). Therefore, one can expect that HCl and HF were also incorporated into comets. The halogens HF, HCl and also HBr (hydrogen bromide) have been measured using ROSINA-DFMS and this contribution will focus on the presence, abundance and variability of halogens in the coma of comet 67P. These results may provide insights on the halogen chemistry in the early solar nebula. (1) Balsiger et al., Space Science Reviews 128, 745. (2) Neufeld & Wolfire, ApJ 706, 1594. (3) Peng et al., ApJ 723, 218. (4) Emprechtinger et al., ApJ 756, 136.