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

September 2020 • 2020ApJ...900L..45B

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

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.

Links

• PDF https://iopscience.iop.org/article/10.3847/2041-8213/abae69/pdf
• PDF https://stacks.iop.org/2041-8205/900/L45/pdf
• PREPRINT http://arxiv.org/abs/2008.05384
• ELECTR https://doi.org/10.3847%2F2041-8213%2Fabae69