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In a new article published on Astronomical Journal, astronomers from the United States, Canada and Europe provide a detailed characterization of the physical properties and orbital evolution of asteroid 2020 CD3, Earth’s second temporary natural satellite, or minimaon. Their results show that 2020 CD3 is a natural body and not a human-made space junk relic.
This image, taken with the 8m Gemini North telescope on Hawaii’s Maunakea, shows Earth’s minimaon 2020 CD3 (center, point source). The image combines three images, each obtained using different filters to produce this composite of color. Image credit: International Gemini Observatory / NOIRLab / NSF / AURA / G. Fedorets.
Asteroids and comets can be temporarily captured by planets as natural satellites. Theoretical models predict that the Earth is also surrounded by a cloud of such temporarily captured asteroids, colloquially called minimaons.
Minimaons possess a number of attributes that make them objects of particular interest.
Because they spend a lot of time near the Earth, they can provide several windows of opportunity for observing the little-studied population of metro-class asteroids.
Due to their relatively long capture duration, accessibility and small size, minima are viable targets for taking the first practical steps in the emerging field of asteroid resource utilization.
Until 2020, only a minimaon had been discovered: 2006 RH120, a tiny near-Earth asteroid with a diameter of about 2-3 m (6.6-9.8 feet).
The second unknown minimum, 2020 CD3, was discovered on February 15, 2020 by the 1.5m Catalina Sky Survey telescope on Mt. Lemmon.
A day later, an alert sent automatically by NASA’s Scout system announced that he had probably been temporarily captured in the Earth-Moon system.
The discovery of an object on a geocentric orbit always raises the suspicion of an artificial origin, but during the 2.5 weeks following its discovery 2020 CD3 cannot be linked to any known artificial object nor can a natural origin be excluded .
On February 26, 2020, the Minor Planet Center then added 2020 CD3 to the asteroid catalog as a temporarily captured object with the request for further follow-up observations to establish its nature.
“The February discovery was significant as the only other documented minimaon astronomers were recorded in 2006, spending about a year in Earth orbit,” said Dr Grigori Fedorets, an astronomer at Queen’s University Belfast.
“We couldn’t miss such a rare opportunity!”
To characterize the minimaon potential, Dr. Fedorets and colleagues obtained high-precision follow-up astrometric observations in February-May 2020 with the Lowell Discovery Telescope (LDT) and several other ground-based observatories.
By measuring the 2020 CD3’s variable brightness over time with the Large Monolithic Imager (LMI) on the LDT, they determined that its rotation speed was about 3 min.
“The turnover rate was probably the biggest unanswered question in this research,” said Dr. Fedorets.
“Our team has shown that it rotates slower than expected for objects in this size range.”
The researchers also used the LMI / LDT combination to precisely measure the position of the 2020 CD3 to refine its orbit.
This information, combined with the physical characteristics of the minimaon – such as an inferred silicate composition – indicate that this is certainly a natural object.
This sets it apart from another minimaon, the recently discovered 2020 SO, which astronomers believe may be the Centaur upper stage rocket booster that helped lift NASA’s Surveyor 2 spacecraft to the moon in 1966.
Dr Fedorets and co-authors also found that 2020 CD3 is between 1 and 1.5 m (3.3-4.9 ft) in diameter and was approximately 13,000 km (8,100 miles) from Earth at the closest approach. .
“This object wasn’t bright enough to be studied for a long time,” said Dr Nick Moskovitz, an astronomer at the Lowell Observatory.
“The fact that we have this telescope in our backyard and we were able to respond quickly made a real difference.”
“The minimums are expected to be discovered in large numbers in the following decade, with the opening of the Vera C. Rubin Observatory scheduled for 2023,” said Dr. Fedorets.
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Grigori Fedorets et al. 2020. Establishing the Minimoon population of the Earth through the characterization of the asteroid 2020 CD3. AJ 160, 277; doi: 10.3847 / 1538-3881 / abc3bc
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