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Ammonium hydrosulphide has long since been postulated to exist at least in certain layers of the giant planets. Its radiation products may be the reason for the red colour seen on Jupiter. Several ammonium salts, the products of NH3 and an acid, have previously been detected at comet 67P/Churyumov-Gerasimenko. The acid H2S is the fifth most abundant molecule in the coma of 67P followed by NH3. In order to look for the salt NH4+SH-, we analysed in situ measurements from the Rosetta/ROSINA Double Focusing Mass Spectrometer during the Rosetta mission. NH3 and H2S appear to be independent of each other when sublimating directly from the nucleus. However, we observe a strong correlation between the two species during dust impacts, clearly pointing to the salt. We find that NH4+SH- is by far the most abundant salt, more abundant in the dust impacts than even water. We also find all previously detected ammonium salts and for the first time ammonium fluoride. The amount of ammonia and acids balance each other, confirming that ammonia is mostly in the form of salt embedded into dust grains. Allotropes S2 and S3 are strongly enhanced in the impacts, while H2S2 and its fragment HS2 are not detected, which is most probably the result of radiolysis of NH4+SH-. This makes a prestellar origin of the salt likely. Our findings may explain the apparent depletion of nitrogen in comets and maybe help to solve the riddle of the missing sulphur in star forming regions., accepted by MNRAS

In-situ study of comet 1P/Halley during its 1986 apparition revealed a surprising abundance of organic coma species. It remained unclear, whether or not these species originated from polymeric matter. Now, high-resolution mass-spectrometric data collected at comet 67P/Churyumov-Gerasimenko by ESA's Rosetta mission unveil the chemical structure of complex cometary organics. Here, we identify an ensemble of individual molecules with masses up to 140 Da while demonstrating inconsistency of the data with relevant amounts of polymeric matter. The ensemble has an average composition of C1H1.56O0.134N0.046S0.017, identical to meteoritic soluble organic matter, and includes a plethora of chain-based, cyclic, and aromatic hydrocarbons at an approximate ratio of 6:3:1. Its compositional and structural properties, except for the H/C ratio, resemble those of other Solar System reservoirs of organics-from organic material in the Saturnian ring rain to meteoritic soluble and insoluble organic matter -, which is compatible with a shared prestellar history. ispartof: NATURE COMMUNICATIONS vol:13 issue:1 ispartof: location:England status: published

Context. In an earlier study, we reported that the ram gauge of the COmet Pressure Sensor (COPS), one of the three instruments of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA), could be used to obtain information about the sublimating content of icy particles, made up of volatiles and conceivably refractories coming from comet 67P/Churyumov-Gerasimenko. Aims. In this work, we extend the investigation to the second COPS gauge, the nude gauge. In particular, we analyse the volume of the volatile content of coma particles, along with a search for possible dependencies between the nude gauge detection rate (i.e. the rate at which icy particles are detected by the nude gauge) and the position of the Rosetta spacecraft. We also investigate the correlations of the nude gauge detection rate with the quantities associated with cometary activity. Methods. We inspected the density measurements made by the nude gauge for features attributable to the presence of icy particles inside the instrument. These data were then analysed statistically based on the amplitude of the feature and on the position of the spacecraft at the time of detection. Results. Although it was not originally designed for such a purpose, the COPS nude gauge has been able to detect ~67 000 features generated by the sublimation of the volatile content of icy particles. The nude gauge detection rate follows a trend that is inversely proportional to the heliocentric distance. This result is interpreted as a confirmation of a possible relation between the nude gauge detection rate and cometary activity. Thus, we compared the former with parameters related to cometary activity and obtained significant correlations, indicating that the frequency of icy particle detection is driven by cometary activity. Furthermore, by representing the volatile part of the icy particles as equivalent spheres with a density of 1 g cm−3, we obtained a range of diameters between 60 and 793 nm, with the smaller ones (

The cyano radical (CN) is one of the most frequently remotely observed species in space, and is also often observed in comets. Data for the inner coma of comet 67P/Churyumov-Gerasimenko collected by the high-resolution Double Focusing Mass Spectrometer (DFMS) on board the Rosetta orbiter revealed an unexpected chemical complexity, and, recently, also more CN than expected from photodissociation of its most likely parent, hydrogen cyanide (HCN). Here, we derive abundances relative to HCN of three cometary nitriles (including structural isomers) from DFMS data. Mass spectrometry of complex mixtures does not always allow isolation of structural isomers, and therefore in our analysis we assume the most stable and abundant (in similar environments) structure, that is HCN for CHN, CH3CN for C2H3N, HC3N for C3HN, and NCCN for C2N2. For cyanoacetylene (HC3N) and acetonitrile (CH3CN), the complete mission time-line was evaluated, while cyanogen (NCCN) was often below the detection limit. By carefully selecting periods where cyanogen was above the detection limit, we were able to follow the abundance ratio between NCCN and HCN from 3.16 au inbound to 3.42 au outbound. These are the first measurements of NCCN in a comet. We find that neither NCCN nor either of the other two nitriles is sufficiently abundant to be a relevant alternative parent to CN.

The ratios of the three stable oxygen isotopes 16O, 17O, and 18O on the Earth and, as far as we know in the Solar system, show variations on the order of a few per cent at most, with a few outliers in meteorites. However, in the interstellar medium there are some highly fractionated oxygen isotopic ratios in some specific molecules. The goal of this work is to investigate the oxygen isotopic ratios in different volatile molecules found in the coma of comet 67P/Churyumov–Gerasimenko and compare them with findings from interstellar clouds in order to assess commonalities and differences. To accomplish this goal, we analysed data from the ROSINA instrument on Rosetta during its mission around the comet. 16O/18O ratios could be determined for O2, methanol, formaldehyde, carbonyl sulfide, and sulfur monoxide/dioxide. For O2 the 16O/17O ratio is also available. Some ratios are strongly enriched in the heavy isotopes, especially for sulfur-bearing molecules and formaldehyde, whereas for methanol the ratios are compatible with the ones in the Solar system. O2 falls in-between, but its oxygen isotopic ratios clearly differ from water, which likely rules out an origin of O2 from water, be it by radiolysis, dismutation during sublimation, or the Eley–Rideal process from water ions hitting the nucleus as postulated in the literature.