Earth's mini-moon was the moon all along

Asteroid 2024 PT5, which almost became a temporary mini-moon to Earth, was recently found to be a broken-off part of the moon itself. This discovery has led scientists to believe there are many more lunar-sourced space rocks waiting to be discovered. Studying these could provide new insight into the moon and its composition.

A moon of Earth's own

While 2024 PT5 never officially joined Earth's orbit, the almost-moon still became a topic of interest and is now understood to very likely be a piece of the actual moon, according to a study published in The Astrophysical Journal Letters. The rock was probably "flung into space by an impact on the lunar surface that occurred sometime within the past tens of thousand years," said The New York Times. "This is a story about the moon as told by asteroid scientists," said Teddy Kareta, a postdoctoral associate at Lowell Observatory in Arizona and the lead author of the study, in a NASA news release. "It's a rare situation where we've gone out to study an asteroid but then strayed into new territory in terms of the questions we can ask of 2024 PT5."

Researchers deduced the object's true nature by observing its movement through space, ruling out that it was human-made space debris. Then they "studied how the sunlight reflected off the small rock" and found it "didn't match that of any known asteroid type" — instead, the "reflected light more closely matched rocks from the moon," said USA Today. While this is convincing evidence that 2024 PT5 was once a piece of the moon, "unless you go and bring a sample back, you cannot tell for sure," said Vishnu Reddy, a professor of planetary science at the University of Arizona, to the Times.

The Week

Escape your echo chamber. Get the facts behind the news, plus analysis from multiple perspectives.

SUBSCRIBE & SAVE

Sign up for The Week's Free Newsletters

From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox.

From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox.

Sign up

Rock the world

Past lunar missions "have provided precious samples for laboratory study, but space rocks chipped off the moon could add another dimension to our understanding," said Earth.com. Locating moon-sourced asteroids may allow researchers to study samples from deeper in the moon, which would otherwise be difficult to extract. Also, "if a lunar asteroid can be directly linked to a specific impact crater on the moon, studying it could lend insights into cratering processes on the pockmarked lunar surface," said the NASA release.

"Mini-moon" is a misnomer for 2024 PT5 because it approached the Earth from the inside, had its "orbit slightly altered by a very close approach with the Earth-moon system" and then receded "away from us on the 'outside' in an overall horseshoe trajectory," Kareta said to CNN. Thus it never truly became a second moon to the Earth. The asteroid is only the second one ever discovered to have lunar origins; scientists predict there may be many more. "As telescopes become more sensitive to smaller asteroids, more potential moon boulders will be discovered, creating an exciting opportunity not only for scientists studying a rare population of asteroids, but also for scientists studying the moon," said the NASA release.