J. Crovisier

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

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Publications (555)1182.41 Total impact

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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).
    05/2014;
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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.
    04/2014;
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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. · 38.60 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.
    01/2014;
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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 01/2014; 238:125–136. · 3.16 Impact Factor
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    ABSTRACT: CBET 3711 available at Central Bureau for Astronomical Telegrams.
    Central Bureau Electronic Telegrams. 11/2013;
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    ABSTRACT: CBET 3686 available at Central Bureau for Astronomical Telegrams.
    Central Bureau Electronic Telegrams. 11/2013;
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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. · 3.16 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.
    10/2013;
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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
    10/2013;
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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.
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    ABSTRACT: 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.
    Planetary and Space Science 09/2013; · 2.11 Impact Factor
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    ABSTRACT: The line emission in the coma was measured in the comets C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR), that were observed on five consecutive nights, 7-11 May 2004, at heliocentric distances of 1.0 and 0.7 AU, respectively, by means of high-resolution spectroscopy using the 10-m Submillimeter Telescope (SMT). We present a search for six parent- and product-volatile species (HCN, H2CO, CO, CS, CH3OH, and HNC) in both comets. Multiline observations of the CH3OH J = 5-4 series allow us to estimate the rotational temperature using the rotation diagram technique. We derive rotational temperatures of 54(9) K for C/2001 Q4 (NEAT) and 119(34) K for C/2002 T7 (LINEAR) that are roughly consistent with observations of other comets at similar distances from the Sun. The gas production rates of material are computed using a spherically symmetric molecular excitation code that includes collisions between neutrals and electrons. We find an HCN production rate of 2.96(5)e26 molec.s-1 for comet C/2001 Q4 (NEAT), corresponding to a mixing ratio with respect to H2O of 1.12(2)e-3. The mean HCN production rate during the observing period is 4.54(10)e26 molec.s-1 for comet C/2002 T7 (LINEAR), which gives a Q_HCN/Q_H2O mixing ratio of 1.51(3)e-3. With systematically lower mixing ratios in comet C/2001 Q4 (NEAT), production rate ratios of the observed species with respect to H2O lie within the typical ranges of dynamically new comets in both objects. We find a relative low abundance of CO in C/2001 Q4 (NEAT) compared to the observed range in other comets based on millimeter/submillimeter observations, and a significant upper limit on the CO production in C/2002 T7 (LINEAR) is derived. Depletion of CO suggests partial evaporation from the surface layers during previous visits to the outer Solar System and agrees with previous measurements of dynamically new comets.
    Astronomy and Astrophysics 08/2013; · 5.08 Impact Factor
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    ABSTRACT: We present Herschel observations of water isotopologues in the atmosphere of the Jupiter-family comet 45P/Honda-Mrkos-Pajdušáková. No HDO emission is detected, with a 3σ upper limit of 2.0 × 10–4 for the D/H ratio. This value is consistent with the earlier Herschel measurement in the Jupiter-family comet 103P/Hartley 2. The canonical value of 3 × 10–4 measured pre-Herschel in a sample of Oort-cloud comets can be excluded at a 4.5σ level. The observations presented here further confirm that a diversity of D/H ratios exists in the comet population and emphasize the need for additional measurements with future ground-based facilities, such as CCAT, in the post-Herschel era.
    The Astrophysical Journal Letters 08/2013; 774(1):L3. · 6.35 Impact Factor
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    ABSTRACT: Little is known about the physical properties of the nuclei of Oort cloud comets. Measuring the thermal emission of a nucleus is one of the few means for deriving its size and constraining some of its thermal properties. We attempted to measure the nucleus size of the Oort cloud comet C/2009 P1 (Garradd). We used the Plateau de Bure Interferometer to measure the millimetric thermal emission of this comet at 157 GHz (1.9 mm) and 266 GHz (1.1 mm). Whereas the observations at 266 GHz were not usable due to bad atmospheric conditions, we derived a 3-sigma upper limit on the comet continuum emission of 0.41 mJy at 157 GHz. Using a thermal model for a spherical nucleus with standard thermal parameters, we found an upper limit of 5.6 km for the radius. The dust contribution to our signal is estimated to be negligible. Given the water production rates measured for this comet and our upper limit, we estimated that Garradd was very active, with an active fraction of its nucleus larger than 50%.
    Astronomy and Astrophysics 07/2013; · 5.08 Impact Factor
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    ABSTRACT: Transneptunian objects (TNOs) are bodies populating the Kuiper Belt and they are believed to retain the most pristine and least altered material of the solar system. The Herschel Open Time Key Program entitled "TNOs are Cool: A survey of the trans-Neptunian region" has been awarded 373 h to investigate the albedo, size distribution and thermal properties of TNOs and Centaurs. Here we focus on the brightest targets observed by both the PACS and SPIRE multiband photometers: the dwarf planet Haumea, six TNOs (Huya, Orcus, Quaoar, Salacia, 2002 UX25, and 2002 TC302), and two Centaurs (Chiron and Chariklo). Flux densities are derived from PACS and SPIRE instruments using optimised data reduction methods. The spectral energy distribution obtained with the Herschel PACS and SPIRE instruments over 6 bands (centred at 70, 100, 160, 250, 350, and 500 $\mu$m), and with Spitzer-MIPS at 23.7 and 71.4 $\mu$m has been modelled with the NEATM thermal model in order to derive the albedo, diameter, and beaming factor. For the Centaurs Chiron and Chariklo and for the 1000 km sized Orcus and Quaoar, a thermophysical model was also run to better constrain their thermal properties. We derive the size, albedo, and thermal properties, including thermal inertia and surface emissivity, for the 9 TNOs and Centaurs. Several targets show a significant decrease in their spectral emissivity longwards of $\sim$300 $\mu$m and especially at 500 $\mu$m. Using our size estimations and the mass values available in the literature, we also derive the bulk densities for the binaries Quaoar/Weywot (2.18$^{+0.43}_{-0.36}$ g/cm$^3$), Orcus/Vanth (1.53$^{+0.15}_{-0.13}$ g/cm$^3$), and Salacia/Actea (1.29$^{+0.29}_{-0.23}$ g/cm$^3$). Quaoar's density is similar to that of the other dwarf planets Pluto and Haumea, and its value implies high contents of refractory materials mixed with ices.
    Astronomy and Astrophysics 05/2013; · 5.08 Impact Factor
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    ABSTRACT: We have obtained production rates of several volatiles (CH3OH, HCN, H13CN, HNC, H2CO, CO, and CS) in comet C/2004 Q2 (Machholz) using the Submillimeter Telescope at the Arizona Radio Observatory. We calculated the synthetic profiles using a radiative transfer code that includes collisions between neutrals and electrons, and the effects of radiative pumping of the fundamental vibrational levels by solar infrared radiation. Furthermore, multiline observations of the CH3OH J = 7-6 series allow us to estimate the rotational temperature using the rotation diagram technique. We find that the CH3OH population distribution of the levels sampled by these lines can be described by a rotational temperature of 40(3) K. Derived mixing ratios relative to hydrogen cyanide are CO/CH3OH/H2CO/CS/HNC/H^{13}CN/HCN = 30.9/24.6/4.8/0.57/0.031/0.013/1 assuming a pointing offset of 8'' due to the uncertain ephemeris at the time of the observations and the telescope pointing error. The measured relative molecular abundances in machholz are between low- to typical values of those obtained in Oort Cloud comets, suggesting that it has visited the inner solar system previously and undergone thermal processing. The HNC/HCN abundance ratio of ∼3.1% is comparable to that found in other comets, accounting for the dependence on the heliocentric distance, and could possibly be explained by ion-molecule chemical processes in the low-temperature atmosphere. From a tentative H^{13}CN detection, the measured value of cratio for the H^{12}CN/H^{13}CN isotopologue pair is consistent with a telluric value. The outgassing variability observed in the HCN production rates over a period of two hours is consistent with the rotation of the nucleus derived using different observational techniques.
    05/2013;
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    ABSTRACT: We obtained high-resolution (λ/Δλ ∼ 28,000) infrared spectra of Comet 103P/Hartley 2 on UT 2010 November 4.6 using the NIRSPEC spectrometer at the W.M. Keck Observatory. Here we present spectra of Hartley 2 between 2.832 and 3.639 μm (3531–2748 cm−1), representing the most complete high-resolution infrared survey of a Jupiter-family comet to date in this wavelength region. We have tabulated rest frequencies, line fluxes, line signal-to-noise ratios and line widths for all detected emissions. Fluorescence models, published line lists and laboratory spectra were used to obtain molecular assignments for detected emissions. Multiple lines of the following species were detected in Hartley 2: H2O, OH, CH3OH, C2H6, HCN, C2H2, H2CO, NH3 and NH2. All identified species seen in this survey have been previously detected in comets. There were 364 distinct emission features present in these spectra, of which 36 were unidentified. We compare the spectrum of Hartley 2 to chemically different Jupiter-family Comets 73P/Schwassmann–Wachmann 3-B and 17P/Holmes in order to obtain additional information on the characteristics of unknown lines through the comparison of relative line fluxes for corresponding emissions in these comets. For the strongest unidentified emissions, additional information was also obtained through a comparison of their spatial distributions in the coma to that of known emission features in Hartley 2. This spectral survey of Hartley 2 provides detailed information about its overall volatile chemistry, provides a comparison to past and future high-resolution infrared datasets, and further characterizes the most promising spectral regions for future molecular searches in comets.
    Icarus 02/2013; 222(2):707–722. · 3.16 Impact Factor
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    ABSTRACT: We conducted high-dispersion spectroscopic observations of Comet 103P/Hartley 2 in the near-infrared wavelength region using the Keck II telescope with NIRSPEC. We obtained observations on four dates, with the last observations performed during the EPOXI closest approach. For this work we focus on the observations performed on UT 2010 October 17 and 21, while observations carried out on UT 2010 September 16 and November 4 have been reported elsewhere. On all dates the spatial distributions in the coma of C2H6, HCN and C2H2 were similar to each other and consistent with the CN-jet morphology observed from optical observations. The spatial distributions in the coma of H2O and CH3OH were also similar to each other, but were generally different from C2H6, HCN and C2H2. There might be two distinct phases of ice in Comet Hartley 2; one is enriched in H2O and CH3OH, and another is enriched in more volatile species (C2H6, C2H2, and HCN). It is possible that highly volatile species like C2H6 were segregated from the H2O matrix when warmer conditions were prevalent. We summarize our spectroscopic observations and report absolute production rates and mixing ratios of parent volatiles. There was no evidence of any significant diversity in the mixing ratios of parent volatiles on different dates. Comet Hartley 2 was normal in CH3OH/H2O, C2H6/H2O, C2H2/H2O, NH3/H2O but depleted in H2CO/H2O and CH4/H2O. OPRs of H2O in Comet Hartley 2 measured in its 2010 apparition were consistent with those observed by the Infrared Satellite Observatory in 1997.
    Icarus 02/2013; 222(2):723–733. · 3.16 Impact Factor

Publication Stats

4k Citations
1,182.41 Total Impact Points

Institutions

  • 1999–2014
    • Paris Diderot University
      Lutetia Parisorum, Île-de-France, France
  • 1995–2013
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, California, United States
  • 2011
    • National Institute of Astrophysics
      • Institute of Physics of Interplanetary Space IFSI
      Roma, Latium, Italy
  • 1970–2009
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France
  • 2005–2007
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
    • University of Hawaiʻi at Mānoa
      • Institute of Astronomy
      Honolulu, HI, United States
  • 2001–2007
    • Johns Hopkins University
      • Applied Physics Laboratory
      Baltimore, Maryland, United States
  • 2003
    • University of Oxford
      Oxford, England, United Kingdom
  • 1995–1998
    • University of Hawaiʻi at Hilo
      Hilo, Hawaii, United States
  • 1981–1991
    • University of Massachusetts Amherst
      • Department of Astronomy
      Amherst Center, Massachusetts, United States
  • 1986
    • University of Granada
      Granata, Andalusia, Spain