The <i>Rosetta</i> Mission and the Chemistry of Organic Species in Comet 67P/Churyumov–Gerasimenko

Comets are regarded as probably the most primitive of solar system objects, preserving a record of the materials from which the solar system aggregated. Key amongst their components are organic compounds – molecules that may trace their heritage to the interstellar medium from which the protosolar nebula eventually emerged. The most recent cometary space mission, Rosetta, carried instruments designed to characterize, in unprecedented detail, the organic species in comet 67P/Churyumov–Gerasimenko (67P). Rosetta was the first mission to match orbits with a comet and follow its evolution over time, and also the first mission to land scientific instruments on a comet surface. Results from the mission revealed a greater variety of molecules than previously identified and indicated that 67P contained both primitive and processed organic entities

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

Similarities in element content between comet 67P/Churyumov–Gerasimenko coma dust and selected meteorite samples

We have analysed the element composition and the context of particles collected within the coma of 67P/Churyumov–Gerasimenko with Rosetta’s COmetary Secondary Ion Mass Analyzer (COSIMA). A comparison has been made between on board cometary samples and four meteorite samples measured in the laboratory with the COSIMA reference model. Focusing on the rock-forming elements, we have found similarities with chondrite meteorites for some ion count ratios. The composition of 67P/Churyumov–Gerasimenko particles measured by COSIMA shows an enrichment in volatile elements compared to that of the investigated Renazzo (CR2) carbonaceous meteorite sample.</p

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

A far-ultraviolet-driven photoevaporation flow observed in a protoplanetary disk

Most low-mass stars form in stellar clusters that also contain massive stars, which are sources of far-ultraviolet (FUV) radiation. Theoretical models predict that this FUV radiation produces photo-dissociation regions (PDRs) on the surfaces of protoplanetary disks around low-mass stars, impacting planet formation within the disks. We report JWST and Atacama Large Millimetere Array observations of a FUV-irradiated protoplanetary disk in the Orion Nebula. Emission lines are detected from the PDR; modelling their kinematics and excitation allows us to constrain the physical conditions within the gas. We quantify the mass-loss rate induced by the FUV irradiation, finding it is sufficient to remove gas from the disk in less than a million years. This is rapid enough to affect giant planet formation in the disk

On the origin and evolution of the material in 67P/Churyumov-Gerasimenko

International audiencePrimitive objects like comets hold important information on the material that formed our solar system. Several comets have been visited by spacecraft and many more have been observed through Earth- and space-based telescopes. Still our understanding remains limited. Molecular abundances in comets have been shown to be similar to interstellar ices and thus indicate that common processes and conditions were involved in their formation. The samples returned by the Stardust mission to comet Wild 2 showed that the bulk refractory material was processed by high temperatures in the vicinity of the early sun. The recent Rosetta mission acquired a wealth of new data on the composition of comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) and complemented earlier observations of other comets. The isotopic, elemental, and molecular abundances of the volatile, semi-volatile, and refractory phases brought many new insights into the origin and processing of the incorporated material. The emerging picture after Rosetta is that at least part of the volatile material was formed before the solar system and that cometary nuclei agglomerated over a wide range of heliocentric distances, different from where they are found today. Deviations from bulk solar system abundances indicate that the material was not fully homogenized at the location of comet formation, despite the radial mixing implied by the Stardust results. Post-formation evolution of the material might play an important role, which further complicates the picture. This paper discusses these major findings of the Rosetta mission with respect to the origin of the material and puts them in the context of what we know from other comets and solar system objects

PDRs4All: A JWST Early Release Science Program on Radiative Feedback from Massive Stars

22 pags., 8 figs., 1 tab.Massive stars disrupt their natal molecular cloud material through radiative and mechanical feedback processes. These processes have profound effects on the evolution of interstellar matter in our Galaxy and throughout the universe, from the era of vigorous star formation at redshifts of 1-3 to the present day. The dominant feedback processes can be probed by observations of the Photo-Dissociation Regions (PDRs) where the far-ultraviolet photons of massive stars create warm regions of gas and dust in the neutral atomic and molecular gas. PDR emission provides a unique tool to study in detail the physical and chemical processes that are relevant for most of the mass in inter-and circumstellar media including diffuse clouds, proto-planetary disks, and molecular cloud surfaces, globules, planetary nebulae, and star-forming regions. PDR emission dominates the infrared (IR) spectra of star-forming galaxies. Most of the Galactic and extragalactic observations obtained with the James Webb Space Telescope (JWST) will therefore arise in PDR emission. In this paper we present an Early Release Science program using the MIRI, NIRSpec, and NIRCam instruments dedicated to the observations of an emblematic and nearby PDR: the Orion Bar. These early JWST observations will provide template data sets designed to identify key PDR characteristics in JWST observations. These data will serve to benchmark PDR models and extend them into the JWST era. We also present the Science-Enabling products that we will provide to the community. These template data sets and Science-Enabling products will guide the preparation of future proposals on star-forming regions in our Galaxy and beyond and will facilitate data analysis and interpretation of forthcoming JWST observations.Support for JWST-ERS program ID 1288 was provided through grants from the STScI under NASA contract NAS5-03127 to STScI (K.G., D.V.D.P., M.R.), Univ. of Maryland (M.W., M.P.), Univ. of Michigan (E.B., F.A.), and Univ. of Toledo (T.S.-Y.L.). O.B. and E.H. are supported by the Programme National “Physique et Chimie du Milieu Interstellaire” (PCMI) of CNRS/INSU with INC/INP co-funded by CEA and CNES, and through APR grants 6315 and 6410 provided by CNES. E. P. and J.C. acknowledge support from the National Science and Engineering Council of Canada (NSERC) Discovery Grant program (RGPIN-2020-06434 and RGPIN-2021-04197 respectively). E.P. acknowledges support from a Western Strategic Support Accelerator Grant (ROLA ID 0000050636). J.R.G. and S.C. thank the Spanish MCINN for funding support under grant PID2019-106110GB-I00. Work by M.R. and Y.O. is carried out within the Collaborative Research Centre 956, subproject C1, funded by the Deutsche Forschungsgemeinschaft (DFG)—project ID 184018867. T.O. acknowledges support from JSPS Bilateral Program, grant No. 120219939. M.P. and M.W. acknowledge support from NASA Astrophysics Data Analysis Program award #80NSSC19K0573. C.B. is grateful for an appointment at NASA Ames Research Center through the San José State University Research Foundation (NNX17AJ88A) and acknowledges support from the Internal Scientist Funding Model (ISFM) Directed Work Package at NASA Ames titled: “Laboratory Astrophysics—The NASA Ames PAH IR Spectroscopic Database.”Peer reviewe

Micrométéorites Concordia : Des Neiges Antarctiques aux Glaces Cométaires

L'étude des micrométéorites CONCORDIA, collectées dans les neiges des régions centrales antarctiques, ouvre une fenêtre pour l'étude de la formation du système solaire. Les micrométéorites ont également pu jouer un rôle dans l'apparition de la vie sur Terre

Micrométéorites Concordia : Des Neiges Antarctiques aux Glaces Cométaires

L'étude des micrométéorites CONCORDIA, collectées dans les neiges des régions centrales antarctiques, ouvre une fenêtre pour l'étude de la formation du système solaire. Les micrométéorites ont également pu jouer un rôle dans l'apparition de la vie sur Terre