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Characterization of Temporarily Captured Minimoon 2020 CD₃ by Keck Time-resolved Spectrophotometry

Bolin, Bryce T. and Fremling, Christoffer and Holt, Timothy R. and Hankins, Matthew J. and Ahumada, Tomás and Anand, Shreya and Bhalerao, Varun and Burdge, Kevin B. and Copperwheat, Chris M. and Coughlin, Michael and Deshmukh, Kunal P. and De, Kishalay and Kasliwal, Mansi M. and Morbidelli, Alessandro and Purdum, Josiah N. and Quimby, Robert and Bodewits, Dennis and Chang, Chan-Kao and Ip, Wing-Huen and Hsu, Chen-Yen and Laher, Russ R. and Lin, Zhong-Yi and Lisse, Carey M. and Masci, Frank J. and Ngeow, Chow-Choong and Tan, Hanjie and Zhai, Chengxing and Burruss, Rick and Dekany, Richard and Delacroix, Alexandre and Duev, Dmitry A. and Graham, Matthew and Hale, David and Kulkarni, Shrinivas R. and Kupfer, Thomas and Mahabal, Ashish and Mróz, Przemyslaw J. and Neill, James D. and Riddle, Reed and Rodriguez, Hector and Smith, Roger M. and Soumagnac, Maayane T. and Walters, Richard and Yan, Lin and Zolkower, Jeffry (2020) Characterization of Temporarily Captured Minimoon 2020 CD₃ by Keck Time-resolved Spectrophotometry. Astrophysical Journal Letters, 900 (2). Art. No. L45. ISSN 2041-8213.

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We present time-resolved visible spectrophotometry of 2020 CD₃, the second known minimoon. The spectrophotometry was taken with the Keck I/Low Resolution Imaging Spectrometer between wavelengths 434 and 912 nm in the B, g, V, R, I, and RG850 filters as it was leaving the Earth–Moon system on 2020 March 23 UTC. The spectrum of 2020 CD₃ resembles V-type asteroids and some lunar rock samples with a 434–761 nm reddish slope of ~18%/100 nm (g–r = 0.62 ± 0.08 and r–i = 0.21 ± 0.06) with an absorption band at ~900 nm corresponding to i–z = −0.54 ± 0.10. Combining our measured H of 31.9 ± 0.1 with an albedo of 0.35 typical for V-type asteroids, we determine 2020 CD₃'s diameter to be ~0.9 ± 0.1 m, making it the first minimoon and one of the smallest asteroids to be spectrally studied. We use our time-series photometry to detect significant periodic light-curve variations with a period of ~573 s and amplitude of ~1. In addition, we extend the observational arc of 2020 CD₃ to 37 days, to 2020 March 23 UTC. From the improved orbital solution for 2020 CD₃, we estimate the likely duration of its capture to be ~2 yr and the nongravitational perturbation on its orbit due to radiation pressure with an area-to-mass ratio of (6.9 ± 2.4) × 10⁻⁴ m² kg⁻¹ implying a density of 2.3 ± 0.8 g cm⁻³, broadly compatible with other meter-scale asteroids and lunar rock. We searched for prediscovery detections of 2020 CD₃ in the Zwicky Transient Facility archive as far back as 2018 October but were unable to locate any positive detections.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Bolin, Bryce T.0000-0002-4950-6323
Fremling, Christoffer0000-0002-4223-103X
Hankins, Matthew J.0000-0001-9315-8437
Ahumada, Tomás0000-0002-2184-6430
Anand, Shreya0000-0003-3768-7515
Bhalerao, Varun0000-0002-6112-7609
Burdge, Kevin B.0000-0002-7226-836X
Copperwheat, Chris M.0000-0001-7983-8698
Coughlin, Michael0000-0002-8262-2924
Deshmukh, Kunal P.0000-0001-5253-3480
De, Kishalay0000-0002-8989-0542
Kasliwal, Mansi M.0000-0002-5619-4938
Morbidelli, Alessandro0000-0001-8476-7687
Quimby, Robert0000-0001-9171-5236
Bodewits, Dennis0000-0002-2668-7248
Chang, Chan-Kao0000-0003-1656-4540
Ip, Wing-Huen0000-0002-3140-5014
Laher, Russ R.0000-0003-2451-5482
Lin, Zhong-Yi0000-0003-3827-8991
Lisse, Carey M.0000-0002-9548-1526
Masci, Frank J.0000-0002-8532-9395
Ngeow, Chow-Choong0000-0001-8771-7554
Zhai, Chengxing0000-0002-0291-4522
Dekany, Richard0000-0002-5884-7867
Duev, Dmitry A.0000-0001-5060-8733
Graham, Matthew0000-0002-3168-0139
Kulkarni, Shrinivas R.0000-0001-5390-8563
Kupfer, Thomas0000-0002-6540-1484
Mahabal, Ashish0000-0003-2242-0244
Mróz, Przemyslaw J.0000-0001-7016-1692
Neill, James D.0000-0002-0466-1119
Riddle, Reed0000-0002-0387-370X
Smith, Roger M.0000-0001-7062-9726
Soumagnac, Maayane T.0000-0001-6753-1488
Walters, Richard0000-0002-1835-6078
Yan, Lin0000-0003-1710-9339
Additional Information:© 2020 The American Astronomical Society. Received 2020 July 24; revised 2020 August 11; accepted 2020 August 12; published 2020 September 15. This work was supported by the GROWTH project, funded by the National Science Foundation under PIRE grant No. 1545949. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. C.F. gratefully acknowledges support of his research by the Heising-Simons Foundation (No. 2018-0907). M.W.C. acknowledges support from the National Science Foundation with grant No. PHY-2010970. Based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. The 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 COO, IPAC, and UW. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC; Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Facilities: Keck I Telescope - , P48 Oschin Schmidt telescope/Zwicky Transient Facility. -
Group:Astronomy Department, Infrared Processing and Analysis Center (IPAC), Zwicky Transient Facility
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Heising-Simons Foundation2018-0907
ZTF partner institutionsUNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Subject Keywords:Asteroids ; Near-Earth objects ; Meteoroids
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Asteroids (72); Near-Earth objects (1092); Meteoroids (1040)
Record Number:CaltechAUTHORS:20200908-080643358
Persistent URL:
Official Citation:Bryce T. Bolin et al 2020 ApJL 900 L45
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105264
Deposited By: Tony Diaz
Deposited On:08 Sep 2020 16:09
Last Modified:23 Oct 2020 17:56

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