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 Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) will answer important questions posed by the mission's main objectives. After Giotto, this will be the first time the volatile part of a comet will be analyzed in situ. This is a very important investigation, as comets, in contrast to meteorites, have maintained most of the volatiles of the solar nebula. To accomplish the very demanding objectives through all the different phases of the comet's activity, ROSINA has unprecedented capabilities including very wide mass range (1 to >300 amu), very high mass resolution (m/Δ m > 3000, i.e. the ability to resolve CO from N2 and 13C from 12CH), very wide dynamic range and high sensitivity, as well as the ability to determine cometary gas velocities, and temperature. ROSINA consists of two mass spectrometers for neutrals and primary ions with complementary capabilities and a pressure sensor. To ensure that absolute gas densities can be determined, each mass spectrometer carries a reservoir of a calibrated gas mixture allowing in-flight calibration. Furthermore, identical flight-spares of all three sensors will serve for detailed analysis of all relevant parameters, in particular the sensitivities for complex organic molecules and their fragmentation patterns in our electron bombardment ion sources

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 ...

A redetermination of the isotopic composition of atmospheric neon gave abundance ratios

Abstract-We report isotopic abundances for C, N, Mg-Al, Si, Ca-Ti, and Fe in 99 presolar silicon carbide (Sic) grains of type X (84 grains from this work and 15 grains from previous studies) from the Murchison CM2 meteorite, ranging in size from 0.5 to 1.5 pm. Carbon was measured in 41 X grains, N in 37 grains, Mg-A1 in 18 grains, Si in 87 grains, Ca-Ti in 25 grains, and Fe in 8 grains. These X grains have 12C/W ratios between 18 and 6800, 14N/15N ratios from 13 to 200, d29SiPSi between -750 and +60k, d30SiPgSi from -770 to -10%0, and 54FePFe ratios that are compatible with solar within the analytical uncertainties of several tens of percent. Many X grains carry large amounts of radiogenic 26Mg (from the radioactive decay of 26A1, half-life = 7 x 105 years) and radiogenic 44Ca (from the radioactive decay of 44Ti, half-life = 60 years). While all X grains but one have radiogenic 26Mg, only -20% of them have detectable amounts of radiogenic 44Ca. Initial 26APAl ratios of up to 0.36 and initial 44TiWTi ratios of up to 0.56 can be inferred. The isotopic data are compared with those expected from the potential stellar sources of Sic dust. Carbon stars, Wolf-Rayet stars, and novae are ruled out as stellar sources of the X grains. The isotopic compositions of C and Fe and abundances of extinct 44Ti are well explained both by type Ia and type I1 supernova (SN) models. The same holds for 26AlPAl ratios, except for the highest 26AlP7Al ratios of >0.2 in some X grains. Silicon agrees qualitatively with SN model predictions, but the observed 29Si/3oSi ratios in the X grains are in most cases too high, pointing to deficiencies in the current understanding of the production of Si in SN environments. The measured 14N/15N ratios are lower than those expected from SN mixing models. This problem can be overcome in a 15 M, type I1 SN if rotational mixing, preferential trapping of N, or both from IsN-rich regions in the ejecta are considered. The isotopic characteristics of C, N, Si, and initial 26AlPAl ratios in small X grains are remarkably similar to those of large X grains (2-10pm). Titanium-44 concentrations are generally much higher in smaller grains, indicative of the presence of Ti-bearing subgrains that might have served as condensation nuclei for Sic. The fraction of X grains among presolar Sic is largely independent of grain size. This implies similar grain-size distributions for Sic from carbon stars (mainstream grains) and supernovae (X grains), a surprising conclusion in view of the different conditions for dust formation in these two types of stellar sources.