Characterization of Temporarily Captured Minimoon 2020 CD3by Keck Time-resolved Spectrophotometry

Bryce T. Bolin, Christoffer Fremling, Timothy R. Holt, Matthew J. Hankins, Tomás Ahumada, Shreya Anand, Varun Bhalerao, Kevin B. Burdge, Chris M. Copperwheat, Michael Coughlin, Kunal P. Deshmukh, Kishalay De, Mansi M. Kasliwal, Alessandro Morbidelli, Josiah N. Purdum, Robert Quimby, Dennis Bodewits, Chan Kao Chang, Wing Huen Ip, Chen Yen HsuRuss R. Laher, Zhong Yi Lin, Carey M. Lisse, Frank J. Masci, Chow Choong Ngeow, Hanjie Tan, Chengxing Zhai, Rick Burruss, Richard Dekany, Alexandre Delacroix, Dmitry A. Duev, Matthew Graham, David Hale, Shrinivas R. Kulkarni, Thomas Kupfer, Ashish Mahabal, Przemyslaw J. Mróz, James D. Neill, Reed Riddle, Hector Rodriguez, Roger M. Smith, Maayane T. Soumagnac, Richard Walters, Lin Yan, Jeffry Zolkower

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3 Scopus citations

Abstract

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.

Original languageEnglish (US)
Article numberL45
JournalAstrophysical Journal Letters
Volume900
Issue number2
DOIs
StatePublished - Sep 10 2020

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