A groundbreaking study in Nature Communications Earth & Environment identifies near-Earth asteroid Kamoʻoalewa as the first known space rock resembling a piece of the Moon. Researchers propose it broke off during an ancient collision on our satellite.
Earth's quasi-satellites are small Solar System bodies that orbit the Sun while staying near our planet. These faint objects are challenging to study. Discovered in 2016, Kamoʻoalewa—the most stable of Earth's five known quasi-satellites—drew scrutiny from University of Arizona astronomers seeking to determine its composition and links to other near-Earth objects.
Visible only briefly each April due to its orbit, this 45- to 58-meter-wide asteroid requires the world's largest telescopes. The team used Arizona's Large Binocular Telescope for precise observations.
Analysis revealed a reddened reflectance spectrum from 0.4 to 2.2 microns, signaling a silicate composition but "with redness beyond what is typically seen among inner Solar System asteroids."
Strikingly, its spectrum closely matched lunar samples returned by NASA's Apollo missions, after comparisons with various analogs.
The asteroid likely entered its current orbit around 500 years ago and will linger for another 300 before departing. Its lunar-like traits point to ejection from the Moon during an ancient asteroid strike.
"If you look at the Moon through a telescope, you see thousands of craters," notes lead author Vishnu Reddy, University of Arizona astronomer. "Material ejected during these impact events should be everywhere." Though over 480 lunar meteorites have reached Earth, "none of these materials have been isolated in space yet," Reddy adds. Kamoʻoalewa may be the first such discovery.
Confirmation could come soon: China plans a 2024 mission to sample a near-Earth object.
