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Multiple Outbursts of Asteroid (6478) Gault

Ye, Quanzhi and Kelley, Michael S. P. and Bodewits, Dennis and Bolin, Bryce and Jones, Lynne and Lin, Zhong-Yi and Bellm, Eric C. and Dekany, Richard and Duev, Dmitry A. and Groom, Steven and Helou, George and Kulkarni, Shrinivas R. and Kupfer, Thomas and Masci, Frank J. and Prince, Thomas A. and Soumagnac, Maayane T. (2019) Multiple Outbursts of Asteroid (6478) Gault. Astrophysical Journal Letters, 874 (2). Art. No. L16. ISSN 2041-8213.

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Main-belt asteroid (6478) Gault unexpectedly sprouted two tails in late 2018 and early 2019, identifying it as a new active asteroid. Here we present observations obtained by the 1.2 m Zwicky Transient Facility survey telescope that provide detailed time-series coverage of the onset and evolution of Gault's activity. Gault exhibited two brightening events, with the first one starting on 2018 October 18 ± 5 days and a second one starting on 2018 December 24 ± 1 days. The amounts of mass released are 2 × 10^7 kg and 1 × 10^6 kg, respectively. Based on photometric measurements, each event persisted for about a month. Gault's color has not changed appreciably over time, with a pre-outburst color of g_(PS1) − r_(PS1) = 0.50 ± 0.04 and g_(PS1) − r_(PS1) = 0.46 ± 0.04 during the two outbursts. Simulations of dust dynamics shows that the ejecta consists of dust grains of up to 10 μm in size that are ejected at low velocities below 1 m s^(-1) regardless of particle sizes. This is consistent with non-sublimation-driven ejection events. The size distribution of the dust exhibits a broken power law, with particles at 10–20 μm following a power law of −2.5 to −3.0, while larger particles follow a steeper slope of −4.0. The derived properties can be explained by either rotational excitation of the nucleus or a merger of a near-contact binary, with the latter scenario to be statistically more likely.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Ye, Quanzhi0000-0002-4838-7676
Kelley, Michael S. P.0000-0002-6702-7676
Bodewits, Dennis0000-0002-2668-7248
Bolin, Bryce0000-0002-4950-6323
Jones, Lynne0000-0001-5916-0031
Lin, Zhong-Yi0000-0003-3827-8991
Bellm, Eric C.0000-0001-8018-5348
Duev, Dmitry A.0000-0001-5060-8733
Groom, Steven0000-0001-5668-3507
Helou, George0000-0003-3367-3415
Kulkarni, Shrinivas R.0000-0001-5390-8563
Kupfer, Thomas0000-0002-6540-1484
Masci, Frank J.0000-0002-8532-9395
Prince, Thomas A.0000-0002-8850-3627
Soumagnac, Maayane T.0000-0001-6753-1488
Additional Information:© 2019. The American Astronomical Society. Received 2019 February 20; revised 2019 March 6; accepted 2019 March 8; published 2019 March 29. We thank the referee for a prompt and helpful review, as well as Charles Bell and Man-To Hui for proofreading and comments. Q.-Z. Ye is supported by the GROWTH project funded by the National Science Foundation under grant No. 1545949. Bryce Bolin and Lynne Jones acknowledge support from the DIRAC Institute in the Department of Astronomy at the University of Washington. The DIRAC Institute is supported through generous gifts from the Charles and Lisa Simonyi Fund for Arts and Sciences, and the Washington Research Foundation. Funding for the Asteroid Institute program is provided by B612 Foundation, W.K. Bowes Jr. Foundation, P. Rawls Family Fund, and two anonymous donors in addition to general support from the B612 Founding Circle ( This work is based on observations obtained with the Samuel Oschin Telescope 48 inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. Major funding has been provided by the U.S. National Science Foundation under grant No. AST-1440341 and by the ZTF partner institutions: the California Institute of Technology, the Oskar Klein Centre, the Weizmann Institute of Science, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron, the University of Wisconsin-Milwaukee, and the TANGO Program of the University System of Taiwan. This work made use of sbpy (, a community-driven Python package for small-body planetary astronomy supported by NASA PDART Grant 80NSSC18K0987. Facility: PO:1.2 m. - Software: Astropy (Astropy Collaboration et al. 2018), Jupyter Notebooks (Kluyver et al. 2016), Matplotlib (Hunter 2007), MERCURY6 (Chambers & Migliorini 1997), sbpy (NASA-Planetary-Science/sbpy), ZChecker (mkelley/zchecker). Note added: During the proofreading stage of this Letter, we learned of an independent paper by Kleyna et al. (2019) describing the original ATLAS detection of the event, as well as the Hubble Space Telescope and ground-based observations from a follow-up campaign. They independently reaches conclusions similar to those presented in this Letter.
Group:Infrared Processing and Analysis Center (IPAC), Zwicky Transient Facility, Astronomy Department
Funding AgencyGrant Number
Charles and Lisa Simonyi Fund for Arts and SciencesUNSPECIFIED
Washington Research FoundationUNSPECIFIED
B612 FoundationUNSPECIFIED
William K. Bowes, Jr. FoundationUNSPECIFIED
P. Rawls Family FundUNSPECIFIED
ZTF partner institutionsUNSPECIFIED
Subject Keywords: comets: individual ((6478 Gault) ; minor planets, asteroids: individual ((6478 Gault)
Issue or Number:2
Record Number:CaltechAUTHORS:20190329-083647975
Persistent URL:
Official Citation:Quanzhi Ye et al 2019 ApJL 874 L16
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:94288
Deposited By: George Porter
Deposited On:29 Mar 2019 16:01
Last Modified:18 Nov 2019 20:47

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