The composition of the neutral gas comas of most comets is dominated by H2O, CO and CO2, typically comprising as much as 95 per cent of the total gas density. In addition, cometary comas have been found to contain a rich array of other molecules, including sulfuric compounds and complex hydrocarbons. Molecular oxygen (O2), however, despite its detection on other icy bodies such as the moons of Jupiter and Saturn, has remained undetected in cometary comas. Here we report in situ measurement of O2 in the coma of comet 67P/Churyumov-Gerasimenko, with local abundances ranging from one per cent to ten per cent relative to H2O and with a mean value of 3.80 ± 0.85 per cent. Our observations indicate that the O2/H2O ratio is isotropic in the coma and does not change systematically with heliocentric distance. This suggests that primordial O2 was incorporated into the nucleus during the comet's formation, which is unexpected given the low upper limits from remote sensing observations. Current Solar System formation models do not predict conditions that would allow this to occur.
The provenance of water and organic compounds on Earth and other terrestrial planets has been discussed for a long time without reaching a consensus. One of the best means to distinguish between different scenarios is by determining the deuterium-to-hydrogen (D/H) ratios in the reservoirs for comets and Earth's oceans. Here, we report the direct in situ measurement of the D/H ratio in the Jupiter family comet 67P/Churyumov-Gerasimenko by the ROSINA mass spectrometer aboard the European Space Agency's Rosetta spacecraft, which is found to be (5.3 ± 0.7) × 10(-4)—that is, approximately three times the terrestrial value. Previous cometary measurements and our new finding suggest a wide range of D/H ratios in the water within Jupiter family objects and preclude the idea that this reservoir is solely composed of Earth ocean-like water.
The detection of glycine and phosphorus in the coma of 67P shows that comets contain all ingredients to help spark life on Earth.
The origin of cometary matter and the potential contribution of comets to inner-planet atmospheres are long-standing problems. During a series of dedicated low-altitude orbits, the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) on the Rosetta spacecraft analyzed the isotopes of xenon in the coma of comet 67P/Churyumov-Gerasimenko. The xenon isotopic composition shows deficits in heavy xenon isotopes and matches that of a primordial atmospheric component. The present-day Earth atmosphere contains 22 ± 5% cometary xenon, in addition to chondritic (or solar) xenon.
Abstract:Comets contain the best-preserved material from the beginning of our planetary system. Their nuclei and comae composition reveal clues about physical and chemical conditions during the early Solar system when comets formed. ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) onboard the Rosetta spacecraft has measured the coma composition of comet 67P/Churyumov-Gerasimenko with well sampled time resolution per rotation. Measurements were made over many comet rotation periods and a wide range of latitudes. These measurements show large fluctuations in composition in a heterogeneous coma that has diurnal and possibly seasonal variations in the major outgassing species: H 2 O, CO, and CO 2 . These results indicate a complex coma-nucleus relationship where seasonal variations may be driven by temperature differences just below the comet surface.One Sentence Summary: ROSINA/DFMS shows that 67P/Churyumov-Gerasimenko has a highly heterogeneous coma with large diurnal and possibly seasonal variations. Main Text:Initially, comets were classified depending on the location where they formed in the protoplanetary disc (1,2). This classification assumed a similar composition of the nucleus within a given formation region. No cometary nucleus composition has been sampled in situ. Rather, it is implicitly assumed that measurements of the outgassing of comets reveal the composition of the volatile components of the nucleus. However, compositional homogeneity of at least one comet was confirmed by studying outgassing from the fragments of the broken up comet Schwassmann-Wachmann 3 (3). Detailed observations of other cometary comae indicated that there is evidence of heterogeneity. Missions to comet Halley detected release of volatiles in multiple jet-like features that were dominantly seen on the sunlit side of the nucleus (4, 5). The Deep Impact mission detected asymmetries in composition in the coma of Tempel 1 (6). In particular, these remote sensing observations at Tempel 1 indicated an absence of correlation between H 2 O and CO 2 in the coma.Detailed, close up cometary images have also showed visible differences between different areas of cometary nuclei. These images suggested that heterogeneity in the coma of a comet may be related to heterogeneity of the nucleus. Observations by EPOXI at Hartley 2 in 2010 near perihelion indicated that the nucleus is complex, with two different sized lobes separated by a middle waist region that is smoother and lighter in color (7). Outgassing from sunlit surfaces of the nucleus revealed that the waist and one of the lobes were very active. A CO 2 source was detected at the small lobe of the comet, while the waist was more active in H 2 O and had a significantly lower CO 2 content. Based on these coma observations, it has been tentatively suggested that the heterogeneity in the comet's nucleus was primordial (7). Seasonal effects could not be ruled out because the observations also showed a complex rotational state for the comet (7). The smaller of the two lobes ...
The ESA Rosetta spacecraft followed comet 67P at a close distance for more than 2 yr. In addition, it deployed the lander Philae on to the surface of the comet. The (surface) composition of the comet is of great interest to understand the origin and evolution of comets. By combining measurements made on the comet itself and in the coma, we probe the nature of this surface material and compare it to remote sensing observations. We compare data from the double focusing mass spectrometer (DFMS) of the ROSINA experiment on ESA's Rosetta mission and previously published data from the two mass spectrometers COSAC (COmetary Sampling And Composition) and Ptolemy on the lander. The mass spectra of all three instruments show very similar patterns of mainly CHO-bearing molecules that sublimate at temperatures of 275 K. The DFMS data also show a great variety of CH-, CHN-, CHS-, CHO 2-and CHNO-bearing saturated and unsaturated species. Methyl isocyanate, propanal and glycol aldehyde suggested by the earlier analysis of the measured COSAC spectrum could not be confirmed. The presence of polyoxymethylene in the Ptolemy spectrum was found to be unlikely. However, the signature of the aromatic compound toluene was identified in DFMS and Ptolemy data. Comparison with remote sensing instruments confirms the complex nature of the organics on the surface of 67P, which is much more diverse than anticipated.
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).
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