Precovery Observations Confirm the Capture Time of Asteroid 2020 CD3 as Earth's Minimoon

Asteroid 2020 CD3 was discovered on 2020 February 15 by the Catalina Sky Survey while it was temporarily captured in a geocentric orbit before escaping Earth's Hill sphere on 2020 March 7. We searched archival images and found precoveries of 2020 CD3 from the Dark Energy Camera and Catalina Sky survey. The Dark Energy Camera images yielded three observations on 2019 January 17, while the Catalina Sky Survey images yielded four observations on 2019 January 24 from the Mt. Lemmon telescope and four observations on 2018 May 9 from the Mt. Bigelow telescope. These precovery observations allowed us to refine the orbit of 2020 CD3 and determine that it was captured in a geocentric orbit on 2017 September 15 after a close approach to the Moon at a distance of 11,974 ± 10 km. We analyzed the trajectory of 2020 CD3 to look for potential Earth impacts within the next 100 years and find a ≳1% probability of an impact between 2061 and 2120 depending on nongravitational force model assumptions. The small size of 2020 CD3, about 1 to 2 m, makes any potential impact harmless.