24 research outputs found

    Water in Comet 2/2003 K4 (LINEAR) with Spitzer

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    We present sensitive 5.5 to 7.6 micron spectra of comet C/2003 K4 (LINEAR) obtained on 16 July 2004 (r_{h} = 1.760 AU, Delta_{Spitzer} = 1.409 AU, phase angle 35.4 degrees) with the Spitzer Space Telescope. The nu_{2} vibrational band of water is detected with a high signal-to-noise ratio (> 50). Model fitting to the best spectrum yields a water ortho-to-para ratio of 2.47 +/- 0.27, which corresponds to a spin temperature of 28.5^{+6.5}_{-3.5} K. Spectra acquired at different offset positions show that the rotational temperature decreases with increasing distance from the nucleus, which is consistent with evolution from thermal to fluorescence equilibrium. The inferred water production rate is (2.43 +/- 0.25) \times 10^{29} molec. s^{-1}. The spectra do not show any evidence for emission from PAHs and carbonate minerals, in contrast to results reported for comets 9P/Tempel 1 and C/1995 O1 (Hale-Bopp). However, residual emission is observed near 7.3 micron the origin of which remains unidentified.Comment: 33 pages, including 11 figures, 2 tables, ApJ 2007 accepte

    Observations of OH in comet Levy with the Nancay radio telescope

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    Due to extremely favorable excitation conditions, comet Levy (1990c) exhibited in August-September 1990 the strongest OH 18-cm signal ever recorded in a comet at the Nancay radio telescope. This unique opportunity was used to measure the OH satellite lines at 1612 and 1721 MHz, to perform extensive mapping of the OH radio emission and to make a sensitive evaluation of the cometary magnetic field, of the H2O outflow velocity and of the OH production rate

    Deuterium Fractionation: the Ariadne's Thread from the Pre-collapse Phase to Meteorites and Comets today

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    The Solar System formed about 4.6 billion years ago from a condensation of matter inside a molecular cloud. Trying to reconstruct what happened is the goal of this chapter. For that, we put together our understanding of Galactic objects that will eventually form new suns and planetary systems, with our knowledge on comets, meteorites and small bodies of the Solar System today. Our specific tool is the molecular deuteration, namely the amount of deuterium with respect to hydrogen in molecules. This is the Ariadne's thread that helps us to find the way out from a labyrinth of possible histories of our Solar System. The chapter reviews the observations and theories of the deuterium fractionation in pre-stellar cores, protostars, protoplanetary disks, comets, interplanetary dust particles and meteorites and links them together trying to build up a coherent picture of the history of the Solar System formation. We emphasise the interdisciplinary nature of the chapter, which gathers together researchers from different communities with the common goal of understanding the Solar System history.Comment: Accepted for publication as a chapter in Protostars and Planets VI, University of Arizona Press (2014), eds. H. Beuther, R. Klessen, C. Dullemond, Th. Hennin

    Model of Dust Thermal Emission of Comet 67p-Churyumov-Gerasimenko for the Rosetta-MIRO Instrument

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    The ESA's Rosetta spacecraft will arrive at comet 67P/Churyumov-Gerasimenko in 2014. The study of gas and dust emission is primary objective of several instruments on the Rosetta spacecraft, including the Microwave Instrument for the Rosetta Orbiter (MIRO). We developed a model of dust thermal emission to estimate the detectability of dust in the vicinity of the nucleus with MIRO. Our model computes the power received by the MIRO antenna in limb viewing as a function of the geometry of the observations and the physical properties of the grains. We show that detection in the millimeter and submillimeter channels can be achieved near perihelion

    The Composition of Comets

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    This paper is the result of the International Cometary Workshop, held in Toulouse, France in April 2014, where the participants came together to assess our knowledge of comets prior to the ESA Rosetta Mission. In this paper, we look at the composition of the gas and dust from the comae of comets. With the gas, we cover the various taxonomic studies that have broken comets into groups and compare what is seen at all wavelengths. We also discuss what has been learned from mass spectrometers during flybys. A few caveats for our interpretation are discussed. With dust, much of our information comes from flybys. They include {\it in situ} analyses as well as samples returned to Earth for laboratory measurements. Remote sensing IR observations and polarimetry are also discussed. For both gas and dust, we discuss what instruments the Rosetta spacecraft and Philae lander will bring to bear to improve our understanding of comet 67P/Churyumov-Gerasimenko as "ground-truth" for our previous comprehensive studies. Finally, we summarize some of the initial Rosetta Mission findings.Comment: To appear in Space Science Review

    Investigating the correlations between water coma emissions and active regions in comet 67P/ Churyumov-Gerasimenko

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    Vibrational emission lines of H2O and CO2 at 2.67 and 4.27 ÎŒm, respectively, were identified by the VIRTIS spectrometer (BockelĂ©e-Morvan et al., 2015; Migliorini et al., 2016; Fink et al., 2016) and mapped from the surface up to about 10 km altitude with a spatial resolution on the order of tens of meters per pixel (Migliorini et al., 2016).Data acquired in April 2015 with the VIRTIS spectrometer on board the Rosetta mission, provided information on the possible correlation between the H2O emission in the inner coma and the exposed water deposits detected in the Hapi region on the 67P/Churyumov-Gerasimenko surface (Migliorini et al., 2106; De Sanctis et al., 2015). Further bright spots attributed to exposed water ice have been identified in other regions by OSIRIS at visible wavelengths (Pommerol, et al., 2015) and confirmed in the infrared by VIRTIS-M in the Imothep region (Filacchione et al., 2016). The small dimensions of these icy spots - approximately 100x100 m (Filacchione et al., 2016) - and the relatively small amount of water ice (about 5%) make uncertain the correlation with the strong emissions in the coma.However, VIRTIS data show that the distribution of jet-like emissions seems to follow the distribution of cliffs and exposed areas identified in the North hemisphere with OSIRIS camera (Vincent et al., 2015). These areas are mainly concentrated in correspondence of comet's rough terrains, while a lack of active regions is observed in the comet's neck. Nevertheless, strong H2O emission is observed above the neck with VIRTIS. This might be a consequence of gas jets that are originated in the surrounding of the neck but converging towards the neck itself. This gaseous activity is the main driver of the dust upwelling (Migliorini et al, 2016; Rinaldi et al., in preparation)In this paper, we investigate the relationship between H2O vapour observed with VIRTIS within 5 km from the 67P/C-G nucleus and the exposed regions identified by OSIRIS on the surface (in the timeframe March to April 2015) with an attempt to address possible variations with the heliocentric distance

    Mapping of thermal properties of comet 67P/C-G and temporal variations

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    The long-term evolution of the surfaces of comets depends mainly on the erosion rate that is driven by the thermal properties of the regolith and the sub-surface material. Following the diurnal and the seasonal thermal cycles, dust and gas are released progressively, increasing the erosion process. The amount of dust released depends on the surface and subsurface temperatures and thus on thermal inertia and bulk composition.The ESA's Rosetta spacecraft has followed the comet 67P/Churyumov-Gerasimenko over several months from 4 AU to 1.28 AU heliocentric distance, and the VIRTIS/Rosetta imaging infrared spectrometer was capable of detecting the thermal emission of the surface longward of 3 microns.The surface temperature was mapped over a large fraction of the nucleus and was previously used to derive thermal inertia of the main geomorphological units.In this presentation, we now focus on two different aspects: (1) We aim to present a complete detailed map of the thermal inertia by combining measurements of similar areas obtained at different viewing angles ; and (2) we track the evolution of the local thermal properties derived over months when the comet was moving towards perihelion. We then discuss and compare our results with the textural features observed at the surface

    Water in small bodies of the Solar System

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    LARGE MOLECULES IN COMETS

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    {D. Bockelee-Morvan, D.C. Lis, J. Wink, et al.,\textit{Astron.\ Astrophys.{J. Crovisier, D. Bockelee-Morvan, N. Biver, etal., \textit{Astron.\ Astrophys.{J. Crovisier, D. Bockelee-Morvan, P. Colom, e t al., \textit{Astron.\ Astrophys.Author Institution: Observatoire de Paris, LESIA, Meudon, F-92195, FranceA fundamental goal of cometary science is to determine the composition of cometary nuclei. Indeed, it provide clues to the origin of cometary material, to the physical/chemical conditions and processes which occurred in the early Solar Nebula and led to the formation of planets, and to the role of cometary impacts in delivering prebiotic molecules to the early Earth. In the absence of a direct analysis of cometary material, the most efficient way to study comet composition is through spectroscopic observations of the comet atmosphere in the radio and infrared domains. I will review the decisive progress obtained in the last decade concerning the composition of cometary volatiles. In the microwave domain, about twenty molecules were detected, the majority of them in comets C/1996 B2 (Hyakutake) and C/1995 O1 (Hale-Hopp) using the IRAM 30-m and Plateau de Bure telescopes, and the Caltech Submillimeter Observatory. Among the most complex ones, are formic acid, formamide, methyl formate and ethylene glycol}, \underline{\textbf{353}}, 1101--1114,2000}}, \underline{\textbf{418}}, L35--L38,2004}. In addition, upper limits were obtained for several species, including complex organic molecules such as ethanol, acetic acid, glycolaldehyde, glycine...}, \underline{\textbf{418}}, 1141--1157, 2004}. In the infrared domain, identified species include hydrocarbons CH4_4, C2_2H2_2, and C2_2H6_6. There are still many unidentified lines in infrared and microwave cometary spectra, showing that available molecular data are still insufficient to analyse these spectra. Several species (e.g., CO, HNC and H2_2CO) exhibit spatial distributions and/or heliocentric behaviors suggesting that they are produced in the coma by the degradation of complex organic material. The presence of complex, still unidentified, species was indicated in the exploration of comet Halley from mass spectroscopy. While detailed studies of composition diversity between comets are going on with the current instrumentation, the detection of new cometary molecules will probably have to await for more sensitive instruments, such as ALMA and large infrared telescopes, or new spectral windows, as the submillimeter domain covered by the Herschel Space Observatory
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