Establishing Earth's Minimoon Population through Characterization of Asteroid 2020 CD3
2020
We report on our detailed characterization of Earth's second known temporary
natural satellite, or minimoon, asteroid 2020 CD3. An artificial origin can be
ruled out based on its area-to-mass ratio and broadband photometry, which
suggest that it is a silicate asteroid belonging to the S or V complex in
asteroid taxonomy. The discovery of 2020 CD3 allows for the first time a
comparison between known minimoons and theoretical models of their expected
physical and dynamical properties. The estimated diameter of 1.2+0.4-0.2 m and
geocentric capture approximately a decade after the first known minimoon, 2006
RH120, are in agreement with theoretical predictions. The capture duration of
2020 CD3 of at least 2.7 yr is unexpectedly long compared to the simulation
average, but it is in agreement with simulated minimoons that have close lunar
encounters, providing additional support for the orbital models. 2020 CD3's
atypical rotation period, significantly longer than theoretical predictions,
suggests that our understanding of meter-scale asteroids needs revision. More
discoveries and a detailed characterization of the population can be expected
with the forthcoming Vera C. Rubin Observatory Legacy Survey of Space and Time.
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