Solar wind sputtering of dust on the surface of 67P/Churyumov-Gerasimenko

International audienceFar away from the Sun, at around 3 AU, the activity of comet 67P/Churyumov-Gerasimenko is low and changes with local time (solar insolation), with location (chemical heterogeneity of the surface), and with season. When the activity is very low because the total cross section of the comet against the Sun is small, the solar wind has access to the surface of the comet and causes ion-induced sputtering of surface material, which we wish to observe.Methods. We used the Double Focussing Mass Spectrometer (DFMS) of the ROSINA experiment on ESA’s Rosetta mission to search for mass spectrometric evidence of sputtered refractory species. In high-resolution mode, DFMS can separate some of the mass peaks of refractory elements from the many volatile species present in the coma.Results. At present, the locations of solar wind surface access are in the southern hemisphere of the comet (the local winter). Of particular interest is sputtering of dust grains on the surface. We observe global averages over the winter hemisphere of the refractory elements Na, K, Si, and Ca, presumably sputtered from grains residing on the surface. Compared to carbonaceous chondrites, the comet has the same Na abundance, is depleted in Ca, and has an excess of K. In addition, for Si the signal strength is strong enough to compile a coarse compositional map of the southern hemisphere. Most, perhaps all, of the observed variation can be explained by the solar wind being affected by the atmosphere of the comet

Sulphur-bearing species in the coma of comet 67P/Churyumov–Gerasimenko

Several sulphur-bearing species have already been observed in different families of comets. However, the knowledge on the minor sulphur species is still limited. The comet’s sulphur inventory is closely linked to the pre-solar cloud and holds important clues to the degree of reprocessing of the material in the solar nebula and during comet accretion. Sulphur in pre-solar clouds is highly depleted, which is quite puzzling as the S/O ratio in the diffuse interstellar medium is cosmic. This work focuses on the abundance of the previously known species H2S, OCS, SO, S2, SO2 and CS2 in the coma of comet 67P/Churyumov–Gerasimenko measured by Rosetta Orbiter Spectrometer for Ion and Neutral Analysis/Double Focusing Mass Spectrometer between equinox and perihelion 2015. Furthermore, we present the first detection of S3, S4, CH3SH and C2H6S in a comet, and we determine the elemental abundance of S/O in the bulk ice of (1.47 ± 0.05) × 10−2. We show that SO is present in the coma originating from the nucleus, but not CS in the case of 67P, and for the first time establish that S2 is present in a volatile and a refractory phase. The derived total elemental sulphur abundance of 67P is in agreement with solar photospheric elemental abundances and shows no sulphur depletion as reported for dense interstellar clouds. Also the presence of S2 at heliocentric distances larger than 3 au indicates that sulphur-bearing species have been processed by radiolysis in the pre-solar cloud and that at least some of the ice from this cloud has survived in comets up the present

Halogens as tracers of protosolar nebula material in comet 67P/Churyumov–Gerasimenko

We report the first in situ detection of halogens in a cometary coma, that of 67P/ChuryumovGerasimenko. Neutral gas mass spectra collected by the European Space Agency’s Rosetta spacecraft during four periods of interest from the first comet encounter up to perihelion indicate that the main halogen-bearing compounds are HF, HCl and HBr. The bulk elemental abundances relative to oxygen are ~8.9 × 10⁻⁵ for F/O, ~1.2 × 10⁻⁴ for Cl/O and ~2.5 × 10⁻⁶ for Br/O, for the volatile fraction of the comet. The cometary isotopic ratios for ³⁷Cl/³⁵Cl and ⁸¹Br/⁷⁹Br match the Solar system values within the error margins. The observations point to an origin of the hydrogen halides in molecular cloud chemistry, with frozen hydrogen halides on dust grains, and a subsequent incorporation into comets as the cloud condensed and the Solar system formed

Novel Time-of-Flight Residual Gas Analyzer (TOF-RGA) for in situ Real-time Process Monitoring

Sensitive gas analyses, in particular in industrial processes, are nowadays performed either via spectroscopy or using quadrupole mass spectrometers; the first method provides a fast but indirect measurement, whereas the second provides in situ measurements of only one species at a time. In this article, we present a novel time-of-flight residual gas analyzer (TOF-RGA) built by the Swiss company Spacetek Technology AG, and show the results of measurements such as the characterization of the FC5311 calibration compound, the detection of naturally abundant noble gases in air, the measurement of a noble gas mixture in the ultra-high vacuum facilities of CERN, and measurements acquired in a X-ray Photoelectron Spectroscopy facility in Germany, to demonstrate the capability of this new TOF-RGA to compete with already existing techniques for the monitoring of the composition of gases in real time (10 times per second), at high resolution (m/?m = 1 200 measured at m/z 132), and with a high sensitivity at ppb level

From Visigoths to Umayyads (672-852) : Coins and monetary circulation in the North of al-Andalus

Le haut Moyen Âge ibérique se caractérise par un changement brutal initié en 711 avec la conquête musulmane du royaume wisigothique. Cet évènement qui bouleversa l’histoire de l’Espagne n’est éclairé que de manière très lacunaire par les sources latines et arabes. Au cours des dernières années, le développement de l’archéologie a néanmoins contribué à une meilleure connaissance de la fin de la monarchie de Tolède et du début d’al-Andalus. Parmi le matériel exhumé, les monnaies sont souvent privilégiées dans les travaux scientifiques et la numismatique bénéficie pour ces périodes d’une bibliographie abondante. Cela permet aujourd’hui une approche plus exhaustive et une meilleure compréhension de leur rôle, de leur utilisation et de leur circulation. Mais les monnaies représentent également un précieux témoignage des difficultés de la fin du royaume wisigothique qui facilitèrent l’entrée et les avancées des troupes arabo-berbères en Hispanie. De même, elles sont les vestiges matériels presqu’exclusifs de la conquête, en particulier pour les régions du Nord du royaume au sujet desquelles les textes se montrent très lacunaires. Enfin, elles furent un outil administratif des Omeyyades au sein d’un émirat dont la centralisation s’accentua avec les réformes réalisées sous ‘Abd al-Raḥmān II (822-852). Cette évolution est perceptible dans la nature même du numéraire employé : alors que les Wisigoths perpétuèrent un monnayage sur le modèle antique en frappant une division du solidus, les musulmans privilégièrent le dirham, rattachant la Péninsule au « monométallisme » argentifère caractéristique du haut Moyen Âge occidental.The Iberian Early Middle Ages are generally characterized by a rough change began in 711 with the Muslim conquest of the Visigothic kingdom. Latin and Arabic textual sources throw few lights on this event that profoundly marked the history of Spain. During the last years, archaeology’s development contributed to a better knowledge about the last years of Toledo Kingdom and beginning of al-Andalus. Among the exhumed material, coins are generally very used in historical studies and numismatic benefits from a large bibliography for this period. That’s why it allows a more exhaustive approach and a better understanding of their role, utilization and circulation. These coins represent an invaluable evidence of the kingdom’s difficulties before the conquest that make easier the Arabic progress in this territory. They are nearly exclusive traces about the conquest, especially for the North part of the kingdom which is little informed by the sources. Finally, they were an administrative tool for Umayyad in the Emirate’s construction and centralization in effect under ‘Abd al-Raḥmān II (822-852). This evolution could be symbolized by monetary changes: Visigoths perpetuated antique coinage with the emission of parts of solidus, Muslims preferred dirham, bringing the Iberian Area under “monometallic” plate zone characteristic of High Middle Ages Occident

Les découvertes de fulûs des fouilles archéologiques de Saragosse

Au regard des trouvailles monétaires fortuites, le nombre de monnaies dont les conditions de découverte peuvent être définies avec précision semble réduit et le contexte stratigraphique demeure bien souvent inconnu. Malgré une bibliographie abondante et une dense couverture scientifique des découvertes, anciennes ou récentes, les monnaies arabo-andalouses ne semblaient pas échapper à ce constat, en particulier en ce qui concerne les monnaies de cuivre (fulûs), qui représentent pourtant la maj..

Ruth Pliego Vázquez, La moneda visigoda (2 vol.)

La singularité des monnaies wisigothiques a suscité l’intérêt des chercheurs et des numismates espagnols dès le xve siècle. Malgré une historiographie relativement abondante et l’utilisation de cette source par les historiens spécialistes du royaume de Tolède, peu de nouveaux travaux avaient vu le jour depuis la publication du catalogue de G. C. Miles en 1952. Après cette période moins prolifique, deux catalogues récents sont à mettre en avant : le Corpus Numorum Visigothorum (2006), adressé ..

Sensitivity and Fragmentation Calibration of the ROSINA Reflectron-type Time-Of-Flight Mass Spectrometer

The goal of this work was to increase the performance and to calibrate one of the ROSINA sensors, the Reflectron-type Time-Of-Flight mass spectrometer, currently flying aboard the ESA Rosetta spacecraft. Different optimization techniques were applied to both the lab and space models, and a static calibration was performed using different gas species expected to be detected in the vicinity of comet 67P/Churyumov-Gerasimenko. The database thus created was successfully applied to space data, giving consistent results with the other ROSINA sensors