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In a new article published in the 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 discovered, or minimoon. Their results prove that 2020 CD3 is a natural body and not a relic of human-made space debris.
This image, taken with the 8m Gemini North Telescope over Maunakea in Hawaii, shows Earth’s 2020 CD3 mini-moon (center, point source). The image combines three images, each obtained using different filters to produce this color composite. Image credit: Gemini International Observatory / NOIRLab / NSF / AURA / G. Fedorets.
Asteroids and comets can be temporarily captured by planets as natural satellites. Theoretical models predict that Earth is also surrounded by a cloud of these temporarily captured asteroids, colloquially called minimoons.
Minimoons have a number of attributes that make them objects of particular interest.
As they spend an extended time close to Earth, they can provide several windows of opportunity for obtaining observations of the poorly studied population of metric class asteroids.
Due to their relatively long capture time, accessibility, and small size, minimoons are viable targets for taking practical first steps in the emerging field of asteroid resource use.
Until 2020, only one minimoon had been discovered – 2006 RH120, a tiny near-Earth asteroid with a diameter of about 2-3 m (6.6 to 9.8 feet).
The second known minimoon, 2020 CD3, was discovered on February 15, 2020 by the 1.5m Catalina Sky Survey Telescope on Mt. Lemmon.
A day later, an alert automatically sent by NASA’s Scout System announced that she had likely been temporarily captured in the Earth-Moon system.
The discovery of an object in a geocentric orbit still raises suspicions of an artificial origin, but for 2.5 weeks after its discovery, the CD3 2020 could not be linked to any known artificial object or rule out a natural origin.
On February 26, 2020, the Minor Planet Center therefore added 2020 CD3 to the asteroid catalog as a temporarily captured object with a request for additional follow-up observations to establish its nature.
“The discovery in February was significant because the only other documented minimoon astronomers were recorded in 2006, spending about a year orbiting the Earth,” said Dr. Grigori Fedorets, astronomer at Queen’s University. from Belfast.
“We couldn’t miss such a rare opportunity!”
To characterize the potential minimoon, Dr Fedorets and his colleagues obtained high precision astrometric tracking observations in February-May 2020 with the Lowell Discovery Telescope (LDT) and several other ground observatories.
By measuring the changing brightness of the CD3 2020 over time with the Large Monolithic Imager (LMI) on the LDT, they established its rotational speed at around 3 min.
“Turnover rate was probably the biggest unanswered question in this research,” said Dr. Fedorets.
“Our team has shown that it spins slower than expected for objects in this size range.”
The researchers also used the LMI / LDT combination to accurately measure the position of the 2020 CD3 to refine its orbit.
This information, combined with the physical characteristics of the minimoon – such as an inferred silicate composition – indicates that it is certainly a natural object.
This sets it apart from another recently discovered minimoon, 2020 SO, which astronomers believe could be the Centaur upper stage rocket thruster that helped lift NASA’s Surveyor 2 spacecraft to the moon in 1966. .
Dr Fedorets and his co-authors also found that the 2020 CD3 is between 1 and 1.5 m (3.3 to 4.9 feet) in diameter and that it approaches at around 13,000 km (8,100 miles). ) from Earth to the nearest approach.
“This object was not bright enough to be studied for very long,” said Dr Nick Moskovitz, astronomer at Lowell Observatory.
“The fact that we have this telescope in our backyard and were able to respond quickly has really made a difference.”
“Minimoons are expected to be discovered in large numbers within the next decade, with the Vera C. Rubin Observatory scheduled to open in 2023,” said Dr Fedorets.
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Fedorets Grigori et al. 2020. Establishment of the Earth’s Minimoon population through the characterization of the asteroid 2020 CD3. A J 160, 277; doi: 10.3847 / 1538-3881 / abc3bc
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