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UA astronomers find key to mysterious near earth objects may be the moon

A team of UA astronomers have discovered a near-Earth object could be made up of moon parts, which would make the tiny object the first of its kind to be discovered.

Using the University of Arizona-managed Large Binocular Telescope on Mount Graham in Southern Arizona, a team of astronomers led by UA planetary sciences graduate student Ben Sharkey found the tiny "quasi-satellite" named  Kamo`oalewa reflected a pattern of light that matched the spectrum of lunar rocks.

Researchers aren't yet be sure how the asteroid may have broken loose from the moon. That's partly because there are no other known asteroids with lunar origins.

So Sharkey didn't think to look there for origins, opting for more traditional reference points when looking at reflected light to find a match.

"I looked through every near-Earth asteroid spectrum we had access to, and nothing matched," said Sharkey.

A debate over Kamo`oalewa's origins between Sharkey and his adviser, UA associate professor of lunar and planetary sciences Vishnu Reddy, led to another three years of hunting for a plausible explanation.

"We doubted ourselves to death," said Reddy, a co-author who started the project in 2016. After missing the chance to observe the asteroid in April 2020 due to a COVID-19 shutdown of the Large Binocular Telescope, the team found the final piece of the puzzle in 2021.

"This spring, we got much needed follow-up observations and went, 'Wow it is real,'" Sharkey said. "It's easier to explain with the moon than other ideas."

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The quasi-satellite is tiny — 150 to 200 feet in diameter — and basically tags along with the Earth on its trip around the sun. That orbital path means Kamo`oalewa can only be seen for a few weeks in April by the largest Earth-bound telescopes.

Kamo`oalewa is about 4 million times fainter than the faintest star the human eye can see in a dark sky.

Little is known about quasi-orbital bodies, but the paper published by the UA team in Nature Communications Earth and Environment provides insight into one such objects composition and possible history.

Kamo`oalewa's orbit is another clue to its lunar origins. Its orbit is similar to the Earth's, but with the slightest tilt. Its orbit is also not typical of near-Earth asteroids, according to study co-author Renu Malhotra, a University of Arizona planetary sciences professor who led the orbit analysis portion of the study.

"It is very unlikely that a garden-variety near-Earth asteroid would spontaneously move into a quasi-satellite orbit like Kamo`oalewa's," said Malhotra, whose lab is working on a paper to further investigate the asteroid's origins. "It will not remain in this particular orbit for very long, only about 300 years in the future, and we estimate that it arrived in this orbit about 500 years ago."

The research was funded by NASA's Near-Earth Object Observations Program and was almost entirely an Arizona production.

It included data from the Lowell Discovery Telescope in Flagstaff. Other co-authors on the paper include Olga Kuhn, Christian Veillet, Barry Rothberg and David Thompson from the Large Binocular Telescope; Audrey Thirouin from Lowell Observatory; and Juan Sanchez from the Planetary Science Institute in Tucson. 

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The construction of the Large Binocular Telescope used in the discovery of Kamo`oalewa's origins.