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Pre-discovery Activity of New Interstellar Comet 2I/Borisov Beyond 5 AU

Ye, Quanzhi and Kelley, Michael S. P. and Bolin, Bryce T. and Bodewits, Dennis and Farnocchia, Davide and Masci, Frank J. and Meech, Karen J. and Micheli, Marco and Weryk, Robert and Bellm, Eric C. and Christensen, Eric and Dekany, Richard and Delacroix, Alexandre and Graham, Matthew J. and Kulkarni, Shrinivas R. and Laher, Russ R. and Rusholme, Ben and Smith, Roger M. (2020) Pre-discovery Activity of New Interstellar Comet 2I/Borisov Beyond 5 AU. Astronomical Journal, 159 (2). Art. No. 77. ISSN 1538-3881.

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Comet 2I/Borisov, the first unambiguous interstellar comet ever found, was discovered in 2019 August at ~3 au from the Sun on its inbound leg. No pre-discovery detection beyond 3 au has yet been reported, mostly due to the comet's proximity to the Sun as seen from the Earth. Here we present a search for pre-discovery detections of comet Borisov using images taken by the Catalina Sky Survey, Pan-STARRS, and the Zwicky Transient Facility (ZTF), with a further comprehensive follow-up campaign being presented in Bolin et al. We identified comet Borisov in ZTF images taken in 2019 May and use these data to update its orbit. This allowed us to identify the comet in images acquired as far back as 2018 December, when it was 7.8 au from the Sun. The comet was not detected in 2018 November when it was 8.6 au from the Sun, possibly implying an onset of activity around this time. This suggests that the activity of the comet is either driven by a more volatile species other than H₂O, such as CO or CO₂, or by exothermic crystallization of amorphous ice. We derive the radius of the nucleus to be <7 km using the non-detection in 2018 November, and estimate an area of ~0.5–10 km² has been active between 2018 December and 2019 September, though this number is model-dependent and is highly uncertain. The behavior of comet Borisov during its inbound leg is observationally consistent with dynamically new comets observed in our solar system, suggesting some similarities between the two.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Ye, Quanzhi0000-0002-4838-7676
Kelley, Michael S. P.0000-0002-6702-7676
Bolin, Bryce T.0000-0002-4950-6323
Bodewits, Dennis0000-0002-2668-7248
Farnocchia, Davide0000-0003-0774-884X
Masci, Frank J.0000-0002-8532-9395
Meech, Karen J.0000-0002-2058-5670
Micheli, Marco0000-0001-7895-8209
Weryk, Robert0000-0002-0439-9341
Bellm, Eric C.0000-0001-8018-5348
Dekany, Richard0000-0002-5884-7867
Graham, Matthew J.0000-0002-3168-0139
Kulkarni, Shrinivas R.0000-0001-5390-8563
Laher, Russ R.0000-0003-2451-5482
Rusholme, Ben0000-0001-7648-4142
Smith, Roger M.0000-0001-7062-9726
Additional Information:© 2020 The American Astronomical Society. Received 2019 November 6; revised 2019 December 5; accepted 2019 December 23; published 2020 January 31. The authors thank Man-To Hui and David Jewitt for discussions of the CO model, as well as George Helou, Matthew Knight, Zhong-Yi Lin, Ralph Roncoli, Qicheng Zhang, and the anonymous referee for comments. M.S.P.K. acknowledges support from NASA grant NNX17AK15G. D.F. conducted this research at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This work is based on observations obtained with the Samuel Oschin 48-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen–Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by Caltech Optical Observatories, the Infrared Processing and Analysis Center, and the University of Washington. Pan-STARRS is supported by the National Aeronautics and Space Administration under grant No. 80NSSC18K0971 issued through the SSO Near Earth Object Observations Program. Facilities: PO:1.2 m - , PS1 - , SO:1.5m - . Software: ZChecker (Kelley et al. 2019).
Group:Infrared Processing and Analysis Center (IPAC), Zwicky Transient Facility, Astronomy Department
Funding AgencyGrant Number
Infrared Processing and Analysis Center (IPAC)UNSPECIFIED
Weizmann Institute of ScienceUNSPECIFIED
Stockholm UniversityUNSPECIFIED
University of MarylandUNSPECIFIED
University of WashingtonUNSPECIFIED
Deutsches Elektronen-SynchrotronUNSPECIFIED
Humboldt UniversityUNSPECIFIED
Los Alamos National LaboratoryUNSPECIFIED
University of Wisconsin-MilwaukeeUNSPECIFIED
Lawrence Berkeley National LaboratoryUNSPECIFIED
Subject Keywords:Comets; Small solar system bodies; Solar system astronomy
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Comets (280); Small solar system bodies (1469); Solar system astronomy (1529)
Record Number:CaltechAUTHORS:20191121-083851194
Persistent URL:
Official Citation:Quanzhi Ye et al 2020 AJ 159 77
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:99978
Deposited By: Tony Diaz
Deposited On:21 Nov 2019 17:31
Last Modified:12 Feb 2021 18:57

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