Menu

Near-Earth Asteroid Could Be Lost Piece Of The Moon, Say Experts

Astronomers have theorized that the mysterious space rock was formed from the moon, and a new study provides the first evidence.

Astronomers believe that a near-Earth asteroid is a long-lost fragment that broke off the moon, according to a new study.

The asteroid known as Kamo`oalewa is a quasi-satellite: a subcategory of asteroids that orbit the sun but stay near our planet. Discovered in 2016 by the Pan-STARRS telescope in Hawaii, Kamo`oalewa is about 150 to 190 feet in diameter and most closely approaches the Earth at approximately 9 million miles. It bears a name taken from native Hawaiian creation myths and alludes to an offspring that travels alone.

In a paper published in the journal Nature, University of Arizona graduate student Ben Sharkey and his team determined that the asteroid’s spectrum, or pattern of reflected light, matches the rocks brought back to Earth by NASA’s Apollo missions to the moon.

From Earth, Kamo`oalewa can only be observed during April because of its orbit. Because it is small, only one of the largest telescopes on Earth can see it. A research team can spot it from the Large Binocular Telescope on Mount Graham in southern Arizona, which is managed by the University of Arizona.

The Large Binocular Telescope, managed by the University of Arizona, consists of a set of two identical 28-foot mirrors, side by side and operating on a common, steerable mount. Located in southeastern Arizona’s Pinaleño Mountains, the telescope is part of the Mount Graham International Observatory. (Courtesy University of Arizona)

Kamo`oalewa is about 4 million times fainter than the faintest star the human eye can see in a dark sky. The tremendous power of the twin telescopes of the Large Binocular Telescope to gather light made the observations possible.

While the reflected light suggests a lunar origin for Kamo`oalewa, the researchers are not certain how it broke away from the moon. There are no other asteroids known to have come from the moon.

“I looked through every near-Earth asteroid spectrum we had access to, and nothing matched,” said Sharkey. Astronomers have previously theorized that the asteroid may have formed from material thrown into orbit by a meteorite strike on the lunar surface.

A bright, young ray impact crater blasted in the eroded wall of the partly buried crater Hedin on the lunar surface. The unnamed crater, just over a mile across, is too small to see from Earth with unaided eyes. The Lunar Reconnaissance Orbiter Camera imaged this crater on Nov. 3, 2018. (NASA/GSFC/Arizona State University)

University of Arizona Professor Vishnu Reddy and Sharkey searched for an explanation for Kamo`oalewa for years. “We doubted ourselves to death,” said study co-author Reddy. Having started the hunt in 2016 and after missing an opportunity to observe the asteroid in April 2020 due to a COVID-19 shutdown, the astronomers got a glimpse of the puzzle in April this year.

“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.”

Kamo`oalewa’s orbit is similar to Earth’s, but has a little tilt. According to study co-author Renu Malhotra, its orbit is not typical of other near-Earth asteroids. “It is very unlikely that a garden-variety near-Earth asteroid would spontaneously move into a quasi-satellite orbit like Kamo`oalewa’s,” she said.

“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,” said Malhotra, a professor of planetary science who led orbit analysis for the study. Her team is conducting further investigation of Kamo`oalewa’s mysterious origins.

Edited by Richard Pretorius and Kristen Butler