Didier Despois

Bio: Didier Despois is an academic researcher from University of Bordeaux. The author has contributed to research in topics: Comet & Plateau de Bure Interferometer. The author has an hindex of 25, co-authored 65 publications receiving 2936 citations. Previous affiliations of Didier Despois include Centre national de la recherche scientifique.

New molecules found in comet C/1995 O1 (Hale-Bopp) Investigating the link between cometary and interstellar material

Abstract: We present millimetre and submillimetre observations of comet C/1995 O1 (Hale-Bopp) undertaken near perihelion with the Caltech Submillimeter Observatory and the 30-m telescope and Plateau-de-Bure interferometer of the Institut de Radioastronomie Millimetrique. From a spectral molecular survey, six new cometary molecular species have been identified for the first time in a comet: SO, SO2, HC3N, NH2CHO, HCOOH, and HCOOCH3. Relative abundances with respect to water are 0.3% (SO), 0.2% (SO2), 0.02% (HC3N), 0.01-0.02% (NH2CHO), 0.09% (HCOOH), and 0.08% (HCOOCH3). Several rotational transitions of OCS and HNCO, whose first identifications were made previously in comet C/1996 B2 (Hyakutake), have also been detected, confirming that these molecular species are ubiquitous compounds of cometary atmospheres. Inferred abundances of OCS and HNCO relative to water in comet Hale-Bopp are 0.4% and 0.1%, respectively. During this observational campaign, we also observed rotational lines of HCN, HNC, CH3CN, CO, CH3OH, H2CO, H2S, and CS. In combination with results of other observations, a comprehensive view of the volatile composition of the coma of comet Hale-Bopp is obtained. A quantitative comparison shows that chemical abundances in comet Hale-Bopp parallel those inferred in interstellar ices, hot molecular cores and bipolar flows around protostars. This suggests that the processes at work in the interstellar medium, in particular grain surface chemistry, played a major role in the formation of cometary ices. It supports models in which cometary volatiles formed in the interstellar medium and suffered little processing in the Solar Nebula.

The composition of ices in comet C/1995 O1 (Hale-Bopp) from radio spectroscopy - Further results and upper limits on undetected species

Abstract: From radio spectroscopic observations of comets, more than 22 molecules, radicals and ions, plus several iso- topologues, were detected, the majority of them being recently revealed in comets C/1996 B2 (Hyakutake) and C/1995 O1 (Hale-Bopp). Among them, 6 molecules were detected for the first time (Bockelee-Morvan et al. 2000) in the course of a spectral survey conducted at radio wavelengths in comet Hale-Bopp with the CSO, the IRAM 30-m telescope and Plateau de Bure interferometer. In addition, many species were searched for unsuccessfully, some of them with stringent upper limits. We present here a review of these observations and further analysis of their results. This include: (i) confirmed detection of acetaldehyde (CH3CHO); (ii) limits on small molecules such as ketene (H2CCO) or methanimine (CH2NH); (iii) limits on the abundance ratios in homologous series such as HC5N/HC3N, ethanol/methanol, acetic acid/formic acid; (iv) searches for precursors of key cometary species such as atomic Na and HNC; (v) constraints on more exotic species ranging from water dimer (H2O)2 to glycine; (vi) detection of the H 34 S isotopic species and independent observations of HDO and DCN; (vii) lim- its on several other deuterated species; (viii) limits on several radicals and ions and a tentative detection of the C2H radical; (ix) the presence of unidentified lines. Typical abundance upper limits of 2-5 ×10 −4 relative to water are achieved for many species. Better upper limits are obtained for some linear molecules with high dipole moments. But more complex molecules such as dimethyl ether or glycine are poorly constrained. These results should give important clues to the chemical composition of cometary ices, to the formation mechanisms of cometary material, and to the chemical processes which occur in the inner coma.

MIRO: Microwave instrument for Rosetta orbiter

Abstract: The European Space Agency Rosetta Spacecraft, launched on March 2, 2004 toward Comet 67P/Churyumov-Gerasimenko, carries a relatively small and lightweight millimeter-submillimeter spectrometer instrument, the first of its kind launched into deep space. The instrument will be used to study the evolution of outgassing water and other molecules from the target comet as a function of heliocentric distance. During flybys of the asteroids (2867) Steins and (21) Lutetia in 2008 and 2010 respectively, the instrument will measure thermal emission and search for water vapor in the vicinity of these asteroids. The instrument, named MIRO (Microwave Instrument for the Rosetta Orbiter), consists of a 30-cm diameter, offset parabolic reflector telescope followed by two heterodyne receivers. Center-band operating frequencies of the receivers are near 190 GHz (1.6 mm) and 562 GHz (0.5 mm). Broadband continuum channels are implemented in both frequency bands for the measurement of near surface temperatures and temperature gradients in Comet 67P/Churyumov-Gerasimenko and the asteroids (2867) Steins and (21) Lutetia. A 4096 channel CTS (Chirp Transform Spectrometer) spectrometer having 180 MHz total bandwidth and 44 kHz resolution is, in addition to the continuum channel, connected to the submillimeter receiver. The submillimeter radiometer/spectrometer is fixed tuned to measure four volatile species – CO, CH3OH, NH3 and three, oxygen-related isotopologues of water, H2 16O, H2 17O and H2 18O. The basic quantities measured with the MIRO instrument are surface temperature, gas production rates and relative abundances, and velocity and excitation temperature of each species, along with their spatial and temporal variability. This paper provides a short discussion of the scientific objectives of the investigation, and a detailed discussion of the MIRO instrument system.

Spectroscopic Monitoring of Comet C/1996 B2 (Hyakutake) with the JCMT and IRAM Radio Telescopes

Abstract: Molecular radio lines were monitored in comet C/1996 B2 (Hyakutake) from 1996 February 10 to June 23, using the James Clerk Maxwell Telescope and the 30 m telescope and the Plateau de Bure interferometer of the Institut de Radioastronomie Millimetrique. We report on observations of HCN, CH3OH, CO, H2CO, CS, and H2S and on the evolution of their production rates with heliocentric distance (rh), from 1.86 down to 0.24 AU at perihelion. Most production rates increased roughly as r down to 0.6 AU preperihelion. Closer to the Sun, they stalled before decreasing beyond 0.6 AU postperihelion, when observations resumed. The CS/HCN ratio varied as r from 1.2 to 0.24 AU. A rapid increase of the mean gas temperature in the coma is measured, and the gas expansion velocity increased from 0.55 to 1.6 km s-1, as the comet approached the Sun from 1.6 to 0.3 AU. Molecular abundances of the minor species around 1 AU are similar to those observed in other comets, while the CO abundance relative to water is high (≈22%). Coarse mapping was used to check the comet's position and to investigate the density distribution of the molecules within the coma. It provides constraints on the size of the extended source of formaldehyde, found to be between 1.2 and 2 times the scale length of H2CO itself. The density distribution of CS is compatible with its production from the photodissociation of a short-lived molecule such as CS2. The density distribution observed for CO can be mostly explained by a nuclear source.

Organic Molecules in the Interstellar Medium, Comets, and Meteorites: A Voyage from Dark Clouds to the Early Earth

Abstract: ▪ Abstract Our understanding of the evolution of organic molecules, and their voyage from molecular clouds to the early solar system and Earth, has changed dramatically. Incorporating recent observ...

The Chemical Composition of Comets—Emerging Taxonomies and Natal Heritage

Abstract: Cometary nuclei contain the least modified material from the formative epoch of our planetary system, and their compositions reflect a range of processes experienced by material prior to its incorporation in the cometary nucleus. Dynamical models suggest that icy bodies in the main cometary reservoirs (Kuiper Belt, Oort Cloud) formed in a range of environments in the protoplanetary disk, and (for the Oort Cloud) even in disks surrounding neighboring stars of the Sun's birth cluster. Photometric and spectroscopic surveys of more than 100 comets have enabled taxonomic groupings based on free radical species and on crystallinity of rocky grains. Since 1985, new surveys have provided emerging taxonomies based on the abundance ratios of primary volatiles. More than 20 primary chemical species are now detected in bright comets. Measurements of nuclear spin ratios (in water, ammonia, and methane) and of isotopic ratios (D/H in water and HCN; 14N/15N in CN and HCN) have provided critical insights on factors affec...

Meteorites and the early solar system II

Abstract: They range in size from microscopic particles to masses of many tons. The geologic diversity of asteroids and other rocky bodies of the solar system are displayed in the enormous variety of textures and mineralogies observed in meteorites. The composition, chemistry, and mineralogy of primitive meteorites collectively provide evidence for a wide variety of chemical and physical processes. This book synthesizes our current understanding of the early solar system, summarizing information about processes that occurred before its formation. It will be valuable as a textbook for graduate education in planetary science and as a reference for meteoriticists and researchers in allied fields worldwide.

Source regions and timescales for the delivery of water to the Earth

Abstract: — In the primordial solar system, the most plausible sources of the water accreted by the Earth were in the outer asteroid belt, in the giant planet regions, and in the Kuiper Belt. We investigate the implications on the origin of Earth's water of dynamical models of primordial evolution of solar system bodies and check them with respect to chemical constraints. We find that it is plausible that the Earth accreted water all along its formation, from the early phases when the solar nebula was still present to the late stages of gas-free sweepup of scattered planetesimals. Asteroids and the comets from the Jupiter-Saturn region were the first water deliverers, when the Earth was less than half its present mass. The bulk of the water presently on Earth was carried by a few planetary embryos, originally formed in the outer asteroid belt and accreted by the Earth at the final stage of its formation. Finally, a late veneer, accounting for at most 10% of the present water mass, occurred due to comets from the Uranus-Neptune region and from the Kuiper Belt. The net result of accretion from these several reservoirs is that the water on Earth had essentially the D/H ratio typical of the water condensed in the outer asteroid belt. This is in agreement with the observation that the D/H ratio in the oceans is very close to the mean value of the D/H ratio of the water inclusions in carbonaceous chondrites.