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The detection of glycine and phosphorus in the coma of 67P shows that comets contain all ingredients to help spark life on Earth.

One sentence summary: The first direct detection of dinitrogen in a cometary coma by Rosetta/ROSINA indicates a low formation temperature of comet 67P/Churyumov-Gerasimenko.3 Abstract: Molecular nitrogen (N 2 ) is thought to have been the most abundant form of nitrogen in the protosolar nebula. N 2 is also the main N-bearing molecule in the atmospheres of Pluto and Triton, and was probably the main nitrogen reservoir from which the giant planets formed. Yet in comets, often considered as the most primitive bodies in the solar system, N 2 has not been detected. Here we report the direct in situ measurement of N 2 in the Jupiter family comet 67P/Churyumov-Gerasimenko made by the ROSINA mass spectrometer aboard the Rosetta spacecraft. A N 2 /CO ratio of 5.70 ± 0.66"3 was measured, corresponding to depletion by a factor of ~25.4 ± 8.9 compared to the protosolar value. This depletion suggests that cometary grains formed at low temperature conditions below ~30 K, and that the amount of N 2 delivered by comets to the terrestrial planets was a small fraction of that contributed by the other N-bearing species.Main text: Thermochemical models of the protosolar nebula (PSN) suggest that molecular nitrogen N 2 was the principal nitrogen species during the disk's phase (1) and that the nitrogen present in the giant planets was accreted in this form (2).

Context. The ESA Rosetta spacecraft (S/C) is tracking comet 67P/Churyumov-Gerasimenko in close vicinity. This prolonged encounter enables studying the evolution of the volatile coma composition. Aims. Our work aims at comparing the diversity of the coma of 67P/Churyumov-Gerasimenko at large heliocentric distance to study the evolution of the comet during its passage around the Sun and at trying to classify it relative to other comets. Methods. We used the Double Focussing Mass Spectrometer (DFMS) of the ROSINA experiment on ESA's Rosetta mission to determine relative abundances of major and minor volatile species. This study is restricted to species that have previously been detected elsewhere. Results. We detect almost all species currently known to be present in cometary coma with ROSINA DFMS. As DFMS measured the composition locally, we cannot derive a global abundance, but we compare measurements from the summer and the winter hemisphere with known abundances from other comets. Differences between relative abundances between summer and winter hemispheres are large, which points to a possible evolution of the cometary surface. This comet appears to be very rich in CO 2 and ethane. Heavy oxygenated compounds such as ethylene glycol are underabundant at 3 AU, probably due to their high sublimation temperatures, but nevertheless, their presence proves that Kuiper belt comets also contain complex organic molecules.

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. MainNitrogen in the volatile part of a comet nucleus is predominantly in the form of NH3 and HCN, which are on average (0.80 ± 0.20) % and (0.21 ± 0.02) %, respectively relative to water, e.g. (1). The numbers for HCN are somewhat uncertain as IR observations generally differ from radio observations (2). Apart from these two molecules, nitrogen bearing species have rather low abundances in comets (2). Especially, neutral N2 escaped detection before the Rosetta mission. Already in 1988, after the Giotto flyby at comet 1P/Halley, Geiss (3) recognized that, while carbon and oxygen relative to silicon are close to solar abundance, comet Halley was clearly lacking nitrogen. One explanation for this depletion at that time was the high volatility of N2, which may not have been condensed in the cometary ice or may have been lost in the last 4.6 Gy. For comet 67P / Churyumov-Gerasimenko (67P hereafter), neutral N2 has now been found on the level of (8.9 ± 2.4) × 10 -4 relative to water (~3 % relative to CO) (4). Recently, a high N2/CO ratio of 6% has been reported for comet C/2016 R2 (Pan-STARRS) (5). This shows that N2 is condensed and stored in cometary ice, but the reported abundances are by far not enough to explain the deficiency in nitrogen. N/C atomic ratio in the solar photosphere is about 0.3 ± 0.1 (6). In the refractory phase, comets are also depleted in nitrogen with N/C = 0.05 ± 0.03 in comet 1P (7) and N/C= 0.035 ± 0.011 in comet 67P (8).While the spread in relative abundances of HCN is quite small among comets, the variation for NH3 seems to be much larger (1). What is quite remarkable is the fact that comets with small perihelion distances seem to have much higher NH3/H2O values (1). This suggests that ammonia has a higher sublimation temperature in comets than water, although for pure ice sublimation temperatures are 90 K and 140 K, respectively. In comet D/2012 S1 (ISON) between 1.2 and 0.34 AU, Di Santi et al. (9) found an increase in NH3/H2O from < 0.78 % up to (3.5 ± 0.3) % and in addition a distribution of NH3, inconsistent with release from ...