J. Crovisier

Paris Diderot University, Lutetia Parisorum, Île-de-France, France

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Publications (557)1248.82 Total impact

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    ABSTRACT: Introduction: Taking advantage of Rosetta's ter-minator orbits around 67P/CG nucleus in December 2014, VIRTIS-M, the mapping channel of the Visible and Infrared Thermal Imaging Spectrometer [1] has carried out systematic observations of the comet limb in the 0.25-5 µm spectral range with the aim to detect fluorescence emissions of gas species like water vapour and carbon dioxide [2]. We report about the first detections of these molecules by VIRTIS-M and correlate them with respect to the nucleus orientation at the time of the observation. These features appear variable in time, depending on numerous parameters like com-et's activity state, relative position of the spacecraft with respect to the nucleus, tangent altitude of the line of sight above the limb, heliocentric distance and solar phase. Water vapour emission at 2.7 µm appears considerably more intense in correspondence of the jets emitted by the active regions in the neck while carbon dioxide emission at 4.25 µm increases in limb observations taken above the head and body regions. Coma observations: In December 2014 VIRTIS has performed an extensive campaign dedicated to 67P/CG coma characterization. These observations consist of repeated limb scans taken on the coma above the illuminated part of the nucleus. From a typical spacecraft altitude above the comet's nucleus of 20 km VIRTIS-M is able to acquire the innermost part of the coma, from the surface up to altitude of about 400-500 m with spatial resolution of about 5 m/pixel. Moreover the 3.7° wide VIRTIS-M field of view allows to image a large region of the sun illuminated coma above the nucleus where the maximum fluorescence emissions of the gasesous species occur. Starting from October 2014, VIRTIS-H channel has detected similar emissions on high-resolution (λ/ Δλ=1300-3000) point spectra in the 2-5 µm range [3]. In the following we describe the first detection of water vapour and carbon dioxide fluorescence emissions detected by VIRTIS-M in two coma observation campaigns carried out in de-cember 2014: 1) session MTP010-STP033, acquired on 2014-12-14 from a spacecraft-comet distance of about 20 km, solar phase of about 91° and spacecraft offnadir angle of 5.4°; 2) session MTP010-STP034 executed on 2014-12-17 from a distance of about 20 km, solar phase 92.7° and spacecraft offnadir angle of 7.1°. The relative position of VIRTIS-M slit and field of view (FOV) at the time of these observations is shown in Fig. 1. On the first half of STP033 sequence VIRTIS has observed the coma above the night hemisphere of the head region (observations I1_00377200411 and I1_00377202271) while on the second half it was pointing above the neck active region (observations I1_00377208511 and I1_00377210370). In MTP010/STP034 VIRTIS-M FOV was spanning across the coma region extending above the neck active area for all the time. At the time of these observations the comet's heliocentric distance was 2.77 AU.
    46th Lunar and Planetary Science Conference, The Woodlands, Texas; 03/2015
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    ABSTRACT: Comparison of their chemical compositions shows, to first order, a good agreement between the cometary and interstellar abundances. However, a complex O-bearing organic molecule, ethylene glycol (CH$_{2}$OH)$_{2}$, seems to depart from this correlation because it was not easily detected in the interstellar medium although it proved to be rather abundant with respect to other O-bearing species in comet Hale-Bopp. Ethylene glycol thus appears, together with the related molecules glycolaldehyde CH$_{2}$OHCHO and ethanol CH$_{3}$CH$_{2}$OH, as a key species in the comparison of interstellar and cometary ices as well as in any discussion on the formation of cometary matter. We focus here on the analysis of ethylene glycol in the nearest and best studied hot core-like region, Orion-KL. We use ALMA interferometric data because high spatial resolution observations allow us to reduce the line confusion problem with respect to single-dish observations since different molecules are expected to exhibit different spatial distributions. Furthermore, a large spectral bandwidth is needed because many individual transitions are required to securely detect large organic molecules. Confusion and continuum subtraction are major issues and have been handled with care. We have detected the aGg' conformer of ethylene glycol in Orion-KL. The emission is compact and peaks towards the Hot Core close to the main continuum peak, about 2" to the south-west; this distribution is notably different from other O-bearing species. Assuming optically thin lines and local thermodynamic equilibrium, we derive a rotational temperature of 145 K and a column density of 4.6 10$^{15}$ cm$^{-2}$. The limit on the column density of the gGg' conformer is five times lower.
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    ABSTRACT: Heat transport and ice sublimation in comets are interrelated processes reflecting properties acquired at the time of formation and during subsequent evolution. The Microwave Instrument on the Rosetta Orbiter (MIRO) acquired maps of the subsurface temperature of comet 67P/Churyumov-Gerasimenko, at 1.6 mm and 0.5 mm wavelengths, and spectra of water vapor. The total H2O production rate varied from 0.3 kg s(-1) in early June 2014 to 1.2 kg s(-1) in late August and showed periodic variations related to nucleus rotation and shape. Water outgassing was localized to the "neck" region of the comet. Subsurface temperatures showed seasonal and diurnal variations, which indicated that the submillimeter radiation originated at depths comparable to the diurnal thermal skin depth. A low thermal inertia (~10 to 50 J K(-1) m(-2) s(-0.5)), consistent with a thermally insulating powdered surface, is inferred. Copyright © 2015, American Association for the Advancement of Science.
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    ABSTRACT: The VIRTIS (Visible, Infrared and Thermal Imaging Spectrometer) instrument on board the Rosetta spacecraft has provided evidence of carbon-bearing compounds on the nucleus of the comet 67P/Churyumov-Gerasimenko. The very low reflectance of the nucleus (normal albedo of 0.060 ± 0.003 at 0.55 micrometers), the spectral slopes in visible and infrared ranges (5 to 25 and 1.5 to 5% kÅ(-1)), and the broad absorption feature in the 2.9-to-3.6-micrometer range present across the entire illuminated surface are compatible with opaque minerals associated with nonvolatile organic macromolecular materials: a complex mixture of various types of carbon-hydrogen and/or oxygen-hydrogen chemical groups, with little contribution of nitrogen-hydrogen groups. In active areas, the changes in spectral slope and absorption feature width may suggest small amounts of water-ice. However, no ice-rich patches are observed, indicating a generally dehydrated nature for the surface currently illuminated by the Sun. Copyright © 2015, American Association for the Advancement of Science.
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    ABSTRACT: Volatile abundances in Jupiter-family Comet 81P/Wild 2 were measured on four dates in February and March 2010 using high-dispersion (λΔλ ∼ 2.5 × 104) infrared spectroscopy with NIRSPEC at the W.M. Keck Observatory. H2O was detected on all dates, including measurements on UT March 29 of lines from the ν2 + ν3 − ν2 hot-band not previously targeted in comets. C2H6 and HCN were detected on three dates, and CH3OH was detected on one date. Tentative detections or upper-limits are reported for CH3OH on other dates, as well as for C2H2, H2CO, and NH3. Abundances of all species relative to H2O are in the typical range with the exception of CH3OH, which is depleted compared to other comets. Gas production was significantly higher in late February than in late March. Rotational temperatures were determined for H2O on UT February 22 and 23 and found to be about 30–40 K. The spatial distributions of H2O, C2H6, and CH3OH are all symmetric and similar to the spatial distribution of the dust continuum. H2O abundances from this work are compared to other measurements from both the 1997 and 2010 apparitions. There is no clear evidence of a change in overall gas productivity between the two apparitions within measurement accuracy. Abundances of C2H2, C2H6, HCN and NH3 are consistent with these species being the primary parents of C2, CN, NH and NH2 as measured at optical wavelengths. Although optically classified as carbon-chain depleted, Wild 2 appears more chemically similar in parent volatile chemistry to carbon-chain typical comets; however, we note that in the small sample of Jupiter-family comets measured to date, each comet is chemically distinct.
    Icarus 08/2014; 238:125–136. DOI:10.1016/j.icarus.2014.05.021 · 2.84 Impact Factor
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    ABSTRACT: This paper reviews the recent findings of the Herschel Solar System Observations Key Program (Hartogh et al. 2009b), as well as ground-based supporting observations, regarding the origin of external oxygen in the environments of Jupiter and Saturn. Herschel-HIFI and PACS observations have been used to shown that the Shoemaker-Levy 9 comet is the source of Jupiter's stratospheric water, and that Enceladus (and its geysers) are most probably the source of water for Saturn and Titan.
    Journées 2014 de la Société Française d’Astronomie & d’Astrophysique (SF2A), Paris; 06/2014
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    ABSTRACT: We performed high-dispersion near-infrared spectroscopic observations of comet C/2010 G2 (Hill) at 2.5 AU from the Sun using NIRSPEC (R 25,000) at the Keck II Telescope on UT 2012 January 9 and 10, about a week after an outburst had occurred. Over the two nights of our observations, prominent emission lines of CH4 and C2H6, along with weaker emission lines of H2O, HCN, CH3OH, and CO were detected. The gas production rate of CO was comparable to that of H2O during the outburst. The mixing ratios of CO, HCN, CH4, C2H6, and CH3OH with respect to H2O were higher than those for normal comets by a factor of five or more. The enrichment of CO and CH4 in comet Hill suggests that the sublimation of these hypervolatiles sustained the outburst of the comet. Some fraction of water in the inner coma might exist as icy grains that were likely ejected from nucleus by the sublimation of hypervolatiles. Mixing ratios of volatiles in comet Hill are indicative of the interstellar heritage without significant alteration in the solar nebula.
    The Astrophysical Journal 05/2014; 788(2):110. DOI:10.1088/0004-637X/788/2/110 · 6.28 Impact Factor
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    ABSTRACT: A spectral survey in the 1 mm wavelength range was undertaken in the long-period comets C/2012 F6 (Lemmon) and C/2013 R1 (Lovejoy) using the 30 m telescope of the Institut de radioastronomie millim\'etrique (IRAM) in April and November-December 2013. We report the detection of ethylene glycol (CH$_2$OH)$_2$ (aGg' conformer) and formamide (NH$_2$CHO) in the two comets. The abundances relative to water of ethylene glycol and formamide are 0.2-0.3% and 0.02% in the two comets, similar to the values measured in comet C/1995 O1 (Hale-Bopp). We also report the detection of HCOOH and CH$_3$CHO in comet C/2013 R1 (Lovejoy), and a search for other complex species (methyl formate, glycolaldehyde).
    Astronomy and Astrophysics 05/2014; 566. DOI:10.1051/0004-6361/201423890 · 4.48 Impact Factor
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    ABSTRACT: We aimed to measure the H2O and dust production rates in C/2006 W3 (Christensen) with the Herschel Space Observatory at a heliocentric distance of ~ 5 AU. We have searched for emission in the H2O and NH3 ground-state rotational transitions at 557 GHz and 572 GHz, simultaneously, with HIFI onboard Herschel on UT 1.5 September 2010. Photometric observations of the dust coma in the 70 and 160 {\mu}m channels were acquired with the PACS instrument on UT 26.5 August 2010. A tentative 4-{\sigma} H2O line emission feature was found in the spectra obtained with the HIFI wide-band and high-resolution spectrometers, from which we derive a water production rate of $2.0(5) \times 10^{27}$ molec. s$^{-1}$. A 3-{\sigma} upper limit for the ammonia production rate of <$1.5 \times 10^{27}$ molec. s$^{-1}$ is obtained taking into account the contribution from all hyperfine components. The blueshift of the water line detected by HIFI suggests preferential emission from the subsolar point. However, it is also possible that water sublimation occurs in small ice-bearing grains that are emitted from an active region on the nucleus surface at a speed of ~ 0.2 km s$^{-1}$. The dust thermal emission was detected in the 70 and 160 {\mu}m filters, with a more extended emission in the blue channel. The dust production rates, obtained for a dust size distribution index that explains the fluxes at the photocenters of the PACS images, lie in the range 70-110 kg s$^{-1}$. Scaling the CO production rate measured post-perihelion at 3.20 and 3.32 AU, these values correspond to a dust-to-gas production rate ratio in the range 0.3-0.4. The dust production rates derived in August 2010 are roughly one order of magnitude lower than in September 2009, suggesting that the dust-to-gas production rate ratio remained approximately constant during the period when the activity became increasingly dominated by CO outgassing.
    Astronomy and Astrophysics 04/2014; 564. DOI:10.1051/0004-6361/201423427 · 4.48 Impact Factor
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    ABSTRACT: The 'snowline' conventionally divides Solar System objects into dry bodies, ranging out to the main asteroid belt, and icy bodies beyond the belt. Models suggest that some of the icy bodies may have migrated into the asteroid belt. Recent observations indicate the presence of water ice on the surface of some asteroids, with sublimation a potential reason for the dust activity observed on others. Hydrated minerals have been found on the surface of the largest object in the asteroid belt, the dwarf planet (1) Ceres, which is thought to be differentiated into a silicate core with an icy mantle. The presence of water vapour around Ceres was suggested by a marginal detection of the photodissociation product of water, hydroxyl (ref. 12), but could not be confirmed by later, more sensitive observations. Here we report the detection of water vapour around Ceres, with at least 10(26) molecules being produced per second, originating from localized sources that seem to be linked to mid-latitude regions on the surface. The water evaporation could be due to comet-like sublimation or to cryo-volcanism, in which volcanoes erupt volatiles such as water instead of molten rocks.
    Nature 01/2014; 505(7484):525-7. DOI:10.1038/nature12918 · 42.35 Impact Factor
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    ABSTRACT: HCl and HF are expected to be the main reservoirs of fluorine and chlorine wherever hydrogen is predominantly molecular. They are found to be strongly depleted in dense molecular clouds, suggesting freeze-out onto grains in such cold environments. We can then expect that HCl and HF were also the major carriers of Cl and F in the gas and icy phases of the outer solar nebula, and were incorporated into comets. We aimed to measure the HCl and HF abundances in cometary ices as they can provide insights on the halogen chemistry in the early solar nebula. We searched for the J(1-0) lines of HCl and HF at 626 and 1232 GHz, respectively, using the HIFI instrument on board the Herschel Space Observatory. HCl was searched for in comets 103P/Hartley 2 and C/2009 P1 (Garradd), whereas observations of HF were conducted in comet C/2009 P1. In addition, observations of H$_2$O and H$_2^{18}$O lines were performed in C/2009 P1 to measure the H$_2$O production rate. Three lines of CH$_3$OH were serendipitously observed in the HCl receiver setting. HCl is not detected, whereas a marginal (3.6-$\sigma$) detection of HF is obtained. The upper limits for the HCl abundance relative to water are 0.011% and 0.022%, for 103P and C/2009 P1, respectively, showing that HCl is depleted with respect to the solar Cl/O abundance by a factor more than 6$^{+6}_{-3}$ in 103P, where the error is related to the uncertainty in the chlorine solar abundance. The marginal HF detection obtained in C/2009 P1 corresponds to an HF abundance relative to water of (1.8$\pm$0.5) $\times$ 10$^{-4}$, which is approximately consistent with a solar photospheric F/O abundance. The observed depletion of HCl suggests that HCl was not the main reservoir of chlorine in the regions of the solar nebula where these comets formed. HF was possibly the main fluorine compound in the gas phase of the outer solar nebula.
    Astronomy and Astrophysics 01/2014; 562. DOI:10.1051/0004-6361/201322939 · 4.48 Impact Factor
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    ABSTRACT: CBET 3711 available at Central Bureau for Astronomical Telegrams.
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    ABSTRACT: CBET 3686 available at Central Bureau for Astronomical Telegrams.
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    ABSTRACT: Comet 103P/Hartley 2 made a close approach to the Earth in October 2010. It was the target of an extensive observing campaign and was visited by the Deep Impact spacecraft (mission EPOXI). We present observations of HCN and CH3OH emission lines conducted with the IRAM Plateau de Bure interferometer on 22-23, 28 October and 4, 5 November 2010 at 1.1, 1.9 and 3.4 mm wavelengths. The thermal emission from the dust coma and nucleus is detected simultaneously. Interferometric images with unprecedented spatial resolution are obtained. A sine-wave variation of the thermal continuum is observed in the 23 October data, that we associate with the nucleus thermal light curve. The nucleus contributes up to 30-55 % of the observed continuum. The large dust-to-gas ratio (in the range 2-6) can be explained by the unusual activity of the comet for its size, which allows decimeter size particles and large boulders to be entrained by the gas. The rotational temperature of CH3OH is measured. We attribute the increase from 35 to 46 K with increasing beam size (from 150 to 1500 km) to radiative processes. The HCN production rate displays strong rotation-induced variations. The HCN production curve, as well as those of CO2 and H2O measured by EPOXI, are interpreted with a geometric model which takes into account the rotation and the shape of the comet. The HCN and H2O production curves are in phase, showing common sources. The 1.7h delay, in average, of HCN and H2O with respect to the CO2 production curve suggests that HCN and H2O are mainly produced by subliming icy grains. The scale length of production of HCN is determined to be on the order of 500-1000 km, implying a mean velocity of 100-200 m/s for the icy grains producing HCN. The modulation of the CO2 prouction and of the velocity offset of the HCN lines are interpreted in terms of localized sources of gas on the nucleus surface.
    Icarus 10/2013; 228. DOI:10.1016/j.icarus.2013.10.010 · 2.84 Impact Factor
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    ABSTRACT: Cometary ices contain material left over from the birth of the solar system, and studying their composition provides an important source of information regarding the physical and chemical conditions of the early Solar Nebula. Previous observations have been unable to ascertain the precise origin of fundamental coma species H2CO, HCN and HNC, and details regarding their possible formation in the coma are currently not well understood. In order to ascertain the chemical origin of these molecules and to place constraints on their coma release mechanisms, spatially and spectrally-resolved molecular emission maps of comets at mm and sub-mm wavelengths are required. In 2013, as part of our Director's Discretionary Time program, observations of the unusually-bright, gas-rich comet F6 (Lemmon) were executed using ALMA in the frequency range 339-362 GHz, covering emission lines from CH3OH, H2CO, HCN and HNC. We will present full details of these unique observations, and an analysis of the observed spectra.
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    ABSTRACT: The two bright comets of the spring of 2013, C/2011 L4 (Pan-STARRS) and C/2012 F6 (Lemmon) were observed on 14-18 March and 5-8 April with the IRAM-30m radiotelescope in Spain. Despite adverse observing conditions we conducted wide frequency surveys (85-93, 166-170, 210-272 GHz) of the two comets using the EMIR receivers and high resolution FTS spectrometer. The wide instantaneous frequency coverage (12-16 GHz dual polarization) enables the coverage of many lines of the same molecular species, making the detection faster. We detected HCN, HNC, CS, HCO+, CH3OH, HC3N, HNCO in comet PanSTARRS and HCN, HNC, HC3N, CH3CN, HNCO, CH3OH, H2CO, H2S, CS, C34S, SO, OCS, H2CS, HCO+ and HDO in comet Lemmon. We present derived production rates and their time evolution. Relative molecular abundances will be discussed in the context of our taxonomic study of Oort-cloud comets [1,2,3]. Comet Lemmon appears intrinsically much more gaseous than comet PanSTARRS and relatively rich in volatiles. [1] Biver et al. (2002), Earth, Moon and Planets 90, 32 [2] Crovisier et al. (2009), Earth, Moon Planet 105, 267 [3] Biver et al. (2011), A&A 528, A142
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    ABSTRACT: We present sub-millimeter observations of the ground-state rotational transition (110-101) of water vapour from comet C/2002 T7 (LINEAR) obtained with the MIRO Instrument on the ESA Rosetta Spacecraft (s/c) Orbiter on April 30, 2004, which is about 7.5 days after its perihelion. The comet was at a distance of 0.63 AU from the Sun and 0.68 AU from the s/c at the time of the observations. The Doppler velocity of the comet relative to the s/c was -72.585 km/s. The ground state rotation transition of ortho-water at 556.936 GHz was observed and integrated for ~ 8 hours using a frequency switched radiometer to provide short and long term stability. MIRO beam size is 7.5 arcmin in terms of full width half maximum, corresponding to a width of 2.2x105 km at the location of the comet. The observed signal line area of the water line spectrum is 4.26 ± 1.17 K km/s, leading to the signal to noise ratio of 3.64. Using a molecular excitation and radiative transfer model and assuming the spherically symmetric and constant radial expansion of gas in the coma, we estimate that the production rate of water is (7.0 ± 0.2)x1E29 molecules/s and the expansion velocity is 1.0 ± 0.2 km/s at the time of the MIRO observation. The present estimation of the water outgassing rate of the comet is in good agreement with other observation-based estimations when the outgassing rates with respect to the time after perihelion are compared.
    Icarus 10/2013; 239. DOI:10.1016/j.icarus.2014.05.004 · 2.84 Impact Factor

Publication Stats

5k Citations
1,248.82 Total Impact Points

Institutions

  • 2011–2015
    • Paris Diderot University
      Lutetia Parisorum, Île-de-France, France
    • National Institute of Astrophysics
      • Institute of Physics of Interplanetary Space IFSI
      Roma, Latium, Italy
    • Max Planck Institute for Solar System Research
      Göttingen, Lower Saxony, Germany
  • 1970–2011
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France
  • 2010
    • Durham University
      Durham, England, United Kingdom
  • 2003–2010
    • Institut de Radioastronomie Millimétrique
      Grenoble, Rhône-Alpes, France
  • 1995–2007
    • Johns Hopkins University
      • Applied Physics Laboratory
      Baltimore, Maryland, United States
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, California, United States
  • 1986–2007
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
    • University of Granada
      Granata, Andalusia, Spain
  • 2005
    • University of Hawaiʻi at Mānoa
      • Institute of Astronomy
      Honolulu, HI, United States
  • 2001
    • European Space Agency
      Lutetia Parisorum, Île-de-France, France
  • 1999
    • Netherlands Institute for Space Research, Utrecht
      Utrecht, Utrecht, Netherlands
    • The Ecological Society of America
      ISO, North Carolina, United States
  • 1998
    • University of Hawaiʻi at Hilo
      Hilo, Hawaii, United States
    • University of Michigan
      Ann Arbor, Michigan, United States
    • Pennsylvania State University
      University Park, Maryland, United States
    • Honolulu University
      Honolulu, Hawaii, United States
  • 1991
    • Institut d'astrophysique de Paris
      Lutetia Parisorum, Île-de-France, France
  • 1981–1991
    • University of Massachusetts Amherst
      • Department of Astronomy
      Amherst Center, Massachusetts, United States
  • 1985
    • University of Minnesota Duluth
      Duluth, Minnesota, United States
  • 1981–1985
    • National Radio Astronomy Observatory
      Charlottesville, Virginia, United States