Observations of the 18-cm OH lines of comet 103P/Hartley 2 at Nan\c{c}ay in support to the EPOXI and Herschel missions

The 18-cm radio lines of the OH radical were observed in comet 103P/Hartley 2 with the Nan\c{c}ay radio telescope in support to its flyby by the EPOXI mission and to observations with the Herschel Space Observatory. The OH lines were detected from 24 September to 15 December 2010. These observations are used to estimate the gas expansion velocity within the coma to 0.83 \pm 0.08 km/s in October 2010. The water production increased steeply but progressively before perihelion, and reached 1.9 \pm 0.3 X 10E28 s-1 just before the EPOXI flyby.Comment: Accepted for publication in Icarus (6 pages, 4 figures

Gas and dust productions of Comet 103P/Hartley 2 from millimetre observations: Interpreting rotation-induced time variations

Comet 103P/Hartley 2 made a close approach to the Earth in October 2010. It was the target of an extensive observing campaign including ground- and orbit-based observatories and was visited by the Deep Impact spacecraft in the framework of its mission extension EPOXI. We present observations of HCN and CH_3OH 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 of ∼100 to ∼500 km are obtained. A sine–wave like 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 emission. The dust thermal emission is used to measure the dust production rate. The inferred 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 due to the small nucleus gravity. The rotational temperature of CH_3OH is measured with beam radii from ∼150 km to ∼1500 km. We attribute the increase from ∼35 K to ∼46 K with increasing beam size to radiative processes. The HCN production rate displays strong rotation-induced temporal variations, varying from ∼0.3 × 10^(25) s^(−1) to ∼2.0 × 10^(25) s^(−1) in the 4–5 November period. The HCN production curve, as well as the CO_2 and H_2O production curves measured by EPOXI, are interpreted with a geometric model which takes into account the complex rotational state of 103P/Hartley 2 and its shape. The HCN and H_2O production curves are in phase, showing that these molecules have common sources. The ∼1.7 h delay, in average, of the HCN and H_2O production curves with respect to the CO_2 production curve suggests that HCN and H_2O 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^(−1) for the icy grains producing HCN. From the time evolution of the insolation of the nucleus, we show that the CO_2 production is modulated by the insolation of the small lobe of the nucleus. The three-cycle pattern of the production curves reported earlier is best explained by an overactivity of the small lobe in the longitude range 0–180°. The good correlation between the insolation of the small lobe and CO_2 production is consistent with CO_2 being produced from small depths below the surface. The time evolution of the velocity offset of the HCN lines, as well as the displacement of the HCN photocenter in the interferometric maps, are overall consistent with this interpretation. Other localized sources of gas on the nucleus surface are also suggested

The chemical diversity of comets

A fundamental question in cometary science is whether the different dynamical classes of comets have different chemical compositions, which would reflect different initial conditions. From the ground or Earth orbit, radio and infrared spectroscopic observations of a now significant sample of comets indeed reveal deep differences in the relative abundances of cometary ices. However, no obvious correlation with dynamical classes is found. Further results come, or are expected, from space exploration. Such investigations, by nature limited to a small number of objects, are unfortunately focussed on short-period comets (mainly Jupiter-family). But these in situ studies provide "ground truth" for remote sensing. We discuss the chemical differences in comets from our database of spectroscopic radio observations, which has been recently enriched by several Jupiter-family and Halley-type comets.Comment: In press in Earth, Moon and Planets (proceedings of the workshop "Future Ground-based Solar System Research: Synergies with Space Probes and Space Telescopes", Portoferraio, Isola d'Elba, Livorno (Italy), 8-12 September 2008). 6 pages with 2 figure

Ethyl alcohol and sugar in comet C/2014 Q2 (Lovejoy)

The presence of numerous complex organic molecules (COMs; defined as those containing six or more atoms) around protostars shows that star formation is accompanied by an increase of molecular complexity. These COMs may be part of the material from which planetesimals and, ultimately, planets formed. Comets represent some of the oldest and most primitive material in the solar system, including ices, and are thus our best window into the volatile composition of the solar protoplanetary disk. Molecules identified to be present in cometary ices include water, simple hydrocarbons, oxygen, sulfur, and nitrogen-bearing species, as well as a few COMs, such as ethylene glycol and glycine. We report the detection of 21 molecules in comet C/2014 Q2 (Lovejoy), including the first identification of ethyl alcohol (ethanol, C_2H_5OH) and the simplest monosaccharide sugar glycolaldehyde (CH_2OHCHO) in a comet. The abundances of ethanol and glycolaldehyde, respectively 5 and 0.8% relative to methanol (0.12 and 0.02% relative to water), are somewhat higher than the values measured in solar-type protostars. Overall, the high abundance of COMs in cometary ices supports the formation through grain-surface reactions in the solar system protoplanetary disk

Leveraging the ALMA Atacama Compact Array for Cometary Science: An Interferometric Survey of Comet C/2015 ER61 (PanSTARRS) and Evidence for a Distributed Source of Carbon Monosulfide

We report the first survey of molecular emission from cometary volatiles using standalone Atacama Compact Array (ACA) observations of the Atacama Large Millimeter/Submillimeter Array (ALMA) toward comet C/2015 ER61 (PanSTARRS) carried out on UT 2017 April 11 and 15, shortly after its April 4 outburst. These measurements of HCN, CS, CH$_3$OH, H$_2$CO, and HNC (along with continuum emission from dust) probed the inner coma of C/2015 ER61, revealing asymmetric outgassing and discerning parent from daughter/distributed source species. This work presents spectrally integrated flux maps, autocorrelation spectra, production rates, and parent scale lengths for each molecule, and a stringent upper limit for CO. HCN is consistent with direct nucleus release in C/2015 ER61, whereas CS, H$_2$CO, HNC, and potentially CH$_3$OH are associated with distributed sources in the coma. Adopting a Haser model, parent scale lengths determined for H$_2$CO (L$_p$ $\sim$ 2200 km) and HNC (L$_p$ $\sim$ 3300 km) are consistent with previous work in comets, whereas significant extended source production (L$_p$ $\sim$ 2000 km) is indicated for CS, suggesting production from an unknown parent in the coma. The continuum presents a point-source distribution, with a flux density implying an excessively large nucleus, inconsistent with other estimates of the nucleus size. It is best explained by the thermal emission of slowly-moving outburst ejectas, with total mass 5--8 $\times$ 10$^{10}$ kg. These results demonstrate the power of the ACA for revealing the abundances, spatial distributions, and locations of molecular production for volatiles in moderately bright comets such as C/2015 ER61

Photodissociation rates of cometary molecules: constraints from interferometric radio observations

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Photodissociation rates of cometary molecules: constraints from interferometric radio observations

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Spatial Distribution Of Molecules Observed In Comet Hale-bopp With The Iram Plateau De Bure Interferometer

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