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

Boissier, Jérémie and Bockelée-Morvan, Dominique and Biver, Nicholas and Colom, Pierre and Crovisier, Jacques and Moreno, Raphael and Zakharov, Vladimir and Groussin, Olivier and Jorda, Laurent and Lis, Darek C. (2014) Gas and dust productions of Comet 103P/Hartley 2 from millimetre observations: Interpreting rotation-induced time variations. Icarus, 228 . pp. 197-216. ISSN 0019-1035. doi:10.1016/j.icarus.2013.10.010.

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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.

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Lis, Darek C.0000-0002-0500-4700
Additional Information:© 2013 Elsevier Inc. Received 19 March 2013. Revised 8 October 2013. Accepted 8 October 2013. Available online 18 October 2013. We thank M. Drahus, for providing us his data set, and M. Belton for useful discussions concerning the complex rotational state of 103P’s nucleus. P. Thomas provided us the shape model and is greatly acknowledged. We also thank S. Besse for providing us unpublished information on H_2O and CO_2 light curves recorded by EPOXI, and M.R. Combi and N. Fougere who kindly communicated to us unpublished results of their 103P’s model. This work is based on observations carried out with the Plateau de Bure Interferometer operated by the IRAM which is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). CSO is supported by the NSF, Award AST-0540882. The research leading to these results received funding from the European Community’s Seventh Framework Programme (FP7/2007–2013) under Grant Agreement No. 229517.
Funding AgencyGrant Number
Institut national des sciences de l'Univers (INSU)UNSPECIFIED
Instituto Geográfico Nacional (IGN)UNSPECIFIED
European Research Council (ERC)229517
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Subject Keywords:Comets, coma; Comets, dust; Radio observations
Record Number:CaltechAUTHORS:20140123-101941464
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Official Citation:Jérémie Boissier, Dominique Bockelée-Morvan, Nicolas Biver, Pierre Colom, Jacques Crovisier, Raphael Moreno, Vladimir Zakharov, Olivier Groussin, Laurent Jorda, Darek C. Lis, Gas and dust productions of Comet 103P/Hartley 2 from millimetre observations: Interpreting rotation-induced time variations, Icarus, Volume 228, 15 January 2014, Pages 197-216, ISSN 0019-1035, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43490
Deposited By: Ruth Sustaita
Deposited On:23 Jan 2014 19:00
Last Modified:10 Nov 2021 16:38

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