COSIMA-Rosetta calibration for in-situ characterization of 67P/Churyumov-Gerasimenko cometary inorganic compounds

20 pages, 3 figures, 5 tablesInternational audienceCOSIMA (COmetary Secondary Ion Mass Analyser) is a time-of-flight secondary ion mass spectrometer (TOF-SIMS) on board the Rosetta space mission. COSIMA has been designed to measure the composition of cometary dust grains. It has a mass resolution m/{\Delta}m of 1400 at mass 100 u, thus enabling the discrimination of inorganic mass peaks from organic ones in the mass spectra. We have evaluated the identification capabilities of the reference model of COSIMA for inorganic compounds using a suite of terrestrial minerals that are relevant for cometary science. Ground calibration demonstrated that the performances of the flight model were similar to that of the reference model. The list of minerals used in this study was chosen based on the mineralogy of meteorites, interplanetary dust particles and Stardust samples. It contains anhydrous and hydrous ferromagnesian silicates, refractory silicates and oxides (present in meteoritic Ca-Al-rich inclusions), carbonates, and Fe-Ni sulfides. From the analyses of these minerals, we have calculated relative sensitivity factors for a suite of major and minor elements in order to provide a basis for element quantification for the possible identification of major mineral classes present in the cometary grains

Multiscale correlated analysis of the Aguas Zarcas CM chondrite

In this paper, we report the results of a campaign of measurements on four fragments of the CM Aguas Zarcas (AZ) meteorite, combining X‐ray computed tomography analysis and Fourier‐transform infrared (FT‐IR) spectroscopy. We estimated a petrologic type for our sampled CM lithology using the two independent techniques, and obtained a type CM2.5, in agreement with previous estimations. By comparing the Si‐O 10‐µm signature of the AZ average FT‐IR spectra with other well‐studied CMs, we place AZ in the context of aqueous alteration of CM parent bodies. Morphological characterization reveals that AZ has heterogeneous distribution of pores and a global porosity of 4.5 ± 0.5 vol%. We show that chondrules have a porosity of 6.3 ± 1 vol%. This larger porosity could be inherited due to various processes such as temperature variation during the chondrule formation and shocks or dissolution during aqueous alteration. Finally, we observed a correlation between 3D distributions of organic matter and mineral at micrometric scales, revealing a link between the abundance of organic matter and the presence of hydrated minerals. This supports the idea that aqueous alteration in AZ’s parent body played a major role in the evolution of the organic matter

Carbon-rich dust in comet 67P/Churyumov-Gerasimenko measured by COSIMA/Rosetta

Cometary ices are rich in CO2, CO and organic volatile compounds, but the carbon content of cometary dust was only measured for the Oort Cloud comet 1P/Halley, during its flyby in 1986. The COmetary Secondary Ion Mass Analyzer (COSIMA)/Rosetta mass spectrometer analysed dust particles with sizes ranging from 50 to 1000 μm, collected over 2 yr, from 67P/Churyumov-Gerasimenko (67P), a Jupiter family comet. Here, we report 67P dust composition focusing on the elements C and O. It has a high carbon content (atomic |${\rm{C}}/{\rm{Si}} = 5.5{\rm{\ }}_{ - 1.2}^{ + 1.4}\ \ {\rm{on\ average}}$ |⁠) close to the solar value and comparable to the 1P/Halley data. From COSIMA measurements, we conclude that 67P particles are made of nearly 50 per cent organic matter in mass, mixed with mineral phases that are mostly anhydrous. The whole composition, rich in carbon and non-hydrated minerals, points to a primitive matter that likely preserved its initial characteristics since the comet accretion in the outer regions of the protoplanetary disc.</p

Nitrogen-to-carbon atomic ratio measured by COSIMA in the particles of comet 67P/Churyumov–Gerasimenko

The COmetary Secondary Ion Mass Analyzer (COSIMA) on board the Rosetta mission has analysed numerous cometary dust particles collected at very low velocities (a few m s−1) in the environment of comet 67P/Churyumov–Gerasimenko (hereafter 67P). In these particles, carbon and nitrogen are expected mainly to be part of the organic matter. We have measured the nitrogen-to-carbon (N/C) atomic ratio of 27 cometary particles. It ranges from 0.018 to 0.06 with an averaged value of 0.035 ± 0.011. This is compatible with the measurements of the particles of comet 1P/Halley and is in the lower range of the values measured in comet 81P/Wild 2 particles brought back to Earth by the Stardust mission. Moreover, the averaged value found in 67P particles is also similar to the one found in the insoluble organic matter extracted from CM, CI and CR carbonaceous chondrites and to the bulk values measured in most interplanetary dust particles and micrometeorites. The close agreement of the N/C atomic ratio in all these objects indicates that their organic matters share some similarities and could have a similar chemical origin. Furthermore, compared to the abundances of all the detected elements in the particles of 67P and to the elemental solar abundances, the nitrogen is depleted in the particles and the nucleus of 67P as was previously inferred also for comet 1P/Halley. This nitrogen depletion could constrain the formation scenarios of cometary nuclei.</p

Etude spectroscopique et chimique de la surface du satellite Io

The aim of this study is to contribute to a better understanding of Io's surface chemical composition. For this purpose, we combined a thermochemical model of Ionian volcanic gases with a spectroscopic and chemical experimental study of low temperature condensed molecules.The thermochemical study is carried out using an improved volcanic gases model, in order to predict the most probable molecules ejected by Io's volcanoes and to follow them during their cooling and the condensation of some of them.The experimental study concerns disulfur monoxide, S2O, a major component predicted by the thermochemical model, and its polymer, polysulfur oxide. We reproduced S2O low temperature condensation, followed its polymerization and measured its infrared spectra in laboratory, under conditions of temperature, pressure, mixing with SO2 and UV-visible radiation simulating Ionian ones.On the one hand, this study improves our knowledge of S2O and of its polymerization mechanism and gives a better idea of polysulfur oxide's structure. On the other hand, our experiments and our spectroscopic results compared to Io's infrared and visible spectra lead us to the conclusion that S2O can not be responsible for red volcanic deposits on Io and that Io's surface is probably mainly composed of sulfur dioxide and a mixture of sulfur S8 and sulfur polymer. To these dominant components, some polysulfur oxide could be added, possibly localized in more restricted volcanic areas.Cette étude a pour but de contribuer aux travaux menés jusqu'ici pour déterminer la composition chimique de la surface du satellite Io. A cette fin, nous avons choisi d'allier modélisation thermochimique des gaz volcaniques ioniens et étude expérimentale spectroscopique et chimique de molécules condensées à basse température. Ainsi, la modélisation thermochimique appliquée au volcanisme ionien permet de suivre le refroidissement des gaz volcaniques émis et met en évidence les séquences de condensation de certaines molécules.A l'issue de cette première partie de l'étude, le monoxyde de disoufre, S2O, apparaissant comme gaz majeur émis par les volcans, est sélectionné pour une étude expérimentale détaillée. Il s'agit là de reproduire en laboratoire la condensation à basse température d'un gaz chargé de S2O et de suivre par spectroscopie infrarouge, son évolution physico-chimique et sa polymérisation, dans des conditions de température, de pression, de mélange avec SO2 et d'irradiation solaire, imitant au mieux celles qui règnent à la surface de Io. Les expériences menées permettent d'approfondir les connaissances chimiques que l'on avait jusque là de S2O et du mécanisme de sa polymérisation en oxyde de polysoufre ainsi que de la structure de ce dernier. De plus, elles conduisent à rejeter la possibilité d'attribuer la couleur rouge de certains dépôts volcaniques à la condensation de S2O à la surface de Io et amènent à penser que cette dernière est très probablement majoritairement composée de dioxyde de soufre et d'un mélange de soufre S8 et de polymère de soufre, auxquels de l'oxyde de polysoufre s'adjoint en plus faible quantité

Etude spectroscopique et chimique de la surface du satellite Io

Cette étude a pour but de contribuer aux travaux menés jusqu'ici pour déterminer la composition chimique de la surface du satellite Io. A cette fin, nous avons choisi d'allier modélisation thermochimique des gaz volcaniques ioniens et étude expérimentale spectroscopique et chimique de molécules condensées à basse température. Ainsi, la modélisation thermochimique appliquée au volcanisme ionien permet de suivre le refroidissement des gaz volcaniques émis et met en évidence les séquences de condensation de certaines molécules. A l'issue de cette première partie de l'étude, le monoxyde de disoufre, S2O, apparaissant comme gaz majeur émis par les volcans, est sélectionné pour une étude expérimentale détaillée. Il s'agit là de reproduire en laboratoire la condensation à basse température d'un gaz chargé de S2O et de suivre par spectroscopie infrarouge, son évolution physico-chimique et sa polymérisation, dans des conditions de température, de pression, de mélange avec SO2 et d'irradiation solaire, imitant au mieux celles qui règnent à la surface de Io. Les expériences menées permettent d'approfondir les connaissances chimiques que l'on avait jusque là de S2O et du mécanisme de sa polymérisation en oxyde de polysoufre ainsi que de la structure de ce dernier. De plus, elles conduisent à rejeter la possibilité d'attribuer la couleur rouge de certains dépôts volcaniques à la condensation de S2O à la surface de Io et amènent à penser que cette dernière est très probablement majoritairement composée de dioxyde de soufre et d'un mélange de soufre S8 et de polymère de soufre, auxquels de l'oxyde de polysoufre s'adjoint en plus faible quantité.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

S2O, polysulfuroxide and sulfur polymer on Io's surface?

International audienceTo settle the question of disulfur monoxide and sulfur monoxide deposition and occurrence on Io's surface, we performed series of laboratory experiments reproducing the condensation of S2O at low temperature. Its polymerization has been monitored by recording infrared spectra under conditions of temperature, pressure, mixing with SO2 and UV–visible radiation simulating that of Io's surface. Our experiments show that S2O condensates are not chemically stable under ionian conditions. We also demonstrate that SO and S2O outgassed by Io's volcanoes and condensing on Io's surface should lead to yellow polysulfuroxide deposits or to white deposits of S2O diluted in sulfur dioxide frost (i.e., S2O/SO2 < 0.1%). Thus S2O condensation cannot be responsible for the red volcanic deposits on Io. Comparison of the laboratory infrared spectra of S2O and polysulfuroxide with NIMS/Galileo infrared spectra of Io's surface leads us to discuss the possible identification of polysulfuroxide. We also recorded the visible transmission spectra of sulfur samples resulting from polysulfuroxide decomposition. These samples consist in a mixture of sulfur polymer and orthorhombic sulfur. Using the optical constants extracted from these measurements, we show that a linear combination of the reflectance spectra of our samples, the reflectance spectrum of orthorhombic S8 sulfur and SO2 reflectance spectrum, leads to a very good matching of Io's visible spectrum between 330 and 520 nm. We conclude then that Io's surface is probably mainly composed of sulfur dioxide and a mixture of sulfur S8 and sulfur polymer. Some polysulfuroxide could also co-exist with these dominant components, but is probably restricted to some volcanic areas

More ion irradiated meteorites: expanding the space weathering view of dark asteroids

International audienceWe performed ion irradiation of dark meteorites as a simulation of slow solar wind irradiation of dark asteroid surfaces. As a follow-up of the reflectance spectroscopy study of several ion-irradiated carbonaceous chondrites from different petrologic groups (CO, CV, CM, CI, C2), we performed new ion irradiation of CK, CR, and CM meteorites to test composition effects. The results of these experiments are used to support current sample return missions Hayabusa2/JAXA and OSIRIS-REx/NASA