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Mapping the Release of Volatiles in the Inner Comae of Comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) Using the Atacama Large Millimeter/Submillimeter Array

Cordiner, M. A. and Remijan, A. J. and Boissier, J. and Milam, S. N. and Mumma, M. J. and Charnley, S. B. and Paganini, L. and Villanueva, G. and Bockelée-Morvan, D. and Kuan, Y.-J and Chuang, Y.-L. and Lis, D. C. and Biver, N. and Crovisier, J. and Minniti, D. and Coulson, I. M. (2014) Mapping the Release of Volatiles in the Inner Comae of Comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) Using the Atacama Large Millimeter/Submillimeter Array. Astrophysical Journal Letters, 792 (1). Art. No. L2. ISSN 2041-8205.

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Results are presented from the first cometary observations using the Atacama Large Millimeter/Submillimeter Array (ALMA), including measurements of the spatially resolved distributions of HCN, HNC, H_2CO, and dust within the comae of two comets: C/2012 F6 (Lemmon) and C/2012 S1 (ISON), observed at heliocentric distances of 1.5 AU and 0.54 AU, respectively. These observations (with angular resolution ≈0."5), reveal an unprecedented level of detail in the distributions of these fundamental cometary molecules, and demonstrate the power of ALMA for quantitative measurements of the distributions of molecules and dust in the inner comae of typical bright comets. In both comets, HCN is found to originate from (or within a few hundred kilometers of) the nucleus, with a spatial distribution largely consistent with spherically symmetric, uniform outflow. By contrast, the HNC distributions are clumpy and asymmetrical, with peaks at cometocentric radii ~500-1000 km, consistent with release of HNC in collimated outflow(s). Compared to HCN, the H_2CO distribution in comet Lemmon is very extended. The interferometric visibility amplitudes are consistent with coma production of H_2CO and HNC from unidentified precursor material(s) in both comets. Adopting a Haser model, the H_2CO parent scale length is found to be a few thousand kilometers in Lemmon and only a few hundred kilometers in ISON, consistent with the destruction of the precursor by photolysis or thermal degradation at a rate that scales in proportion to the solar radiation flux.

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URLURL TypeDescription Paper
Lis, D. C.0000-0002-0500-4700
Additional Information:© 2014 American Astronomical Society. Received 2014 June 17; accepted 2014 July 9; published 2014 August 11. This work was supported by the NASA Astrobiology Institute through the Goddard Center for Astrobiology, and NASA’s Planetary Atmospheres and Planetary Astronomy Programs. It makes use of the following ALMA data: ADS/JAO.ALMA #2012.A.00020.S and #2012.A.00033.S. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. D.C.L. is supported by NASA through JPL/Caltech. D.M. is supported by Basal CATA PFB-06 and the ICM MAS. Y.J.K. is supported by NSC grants 99-2112-M-003-003-MY3 and 100-2119-M-003-001-MY3.
Funding AgencyGrant Number
National Science Council (Taipei)99-2112-M-003-003-MY3
National Science Council (Taipei)100-2119-M-003-001-MY3
Subject Keywords:comets: individual (C/2012 S1 (ISON), C/2012 F6 (Lemmon)); techniques: interferometric
Issue or Number:1
Record Number:CaltechAUTHORS:20141006-081141376
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Official Citation:Mapping the Release of Volatiles in the Inner Comae of Comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) Using the Atacama Large Millimeter/Submillimeter Array M. A. Cordiner et al. 2014 ApJ 792 L2
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50196
Deposited By: Ruth Sustaita
Deposited On:06 Oct 2014 15:53
Last Modified:03 Oct 2019 07:21

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