Earth Had a Tiny Second Moon for a Few Months. It Might Be A Chunk of the Moon
For a few months, Earth had a second moon — a tiny asteroid that may have been a piece of our own Moon
Last year, Earth briefly gained a second moon. Not a grand, glowing orb like the one we know, but a modest space rock, just 33 feet across, that lingered in our planet’s vicinity for a few months. Astronomers named it 2024 PT5, and for a fleeting moment, it captured the imagination of scientists and skywatchers alike. Now, a new study suggests this tiny visitor wasn’t just any asteroid — it might be a piece of the Moon itself, ejected into space thousands of years ago after a violent impact on the lunar surface.
The discovery offers a surprising glimpse into the dynamic history of our Moon and the hidden population of lunar fragments that may be drifting through space, waiting to be found.
A Mini-Moon with a Lunar Connection
2024 PT5 was first spotted on August 7, 2024, by the Asteroid Terrestrial-impact Last Alert System (ATLAS), a network of telescopes designed to detect near-Earth objects. The asteroid’s orbit around the Sun closely matched Earth’s, hinting that it might have originated nearby. But it wasn’t until astronomers analyzed the light reflecting off its surface that they began to suspect its true origins.
“We had a general idea that this asteroid may have come from the Moon, but the smoking gun was when we found out that it was rich in silicate minerals — not the kind that are seen on asteroids but those that have been found in lunar rock samples,” Teddy Kareta, an astronomer at Lowell Observatory in Arizona and lead author of the study, said in a press release.
The asteroid’s spectral signature — the pattern of light it reflects — closely matched that of lunar rocks brought back by Apollo missions and Soviet robotic landers. This, combined with its unusual orbit, led researchers to conclude that 2024 PT5 was likely a fragment of the Moon, ejected into space after a powerful impact.
But how did it end up back near Earth? The answer lies in the complex dance of gravity and orbital mechanics. Unlike most asteroids, which originate in the belt between Mars and Jupiter, 2024 PT5 appears to have been flung into space by a lunar impact, eventually finding its way into an orbit that brought it close to Earth. Like salmon that navigate back to their spawning site after years in the ocean, this tiny moonlet periodically circles back home after spending some time traveling the inner solar system.
Not a Space Junk, but A Piece of Lunar History
One of the first challenges for the research team was ruling out the possibility that 2024 PT5 was human-made space debris. In 2020, Earth briefly captured another “mini-moon” that turned out to be an old rocket booster. To confirm that 2024 PT5 was a natural object, scientists studied how it moved through space.
“Human-made debris is usually relatively light and gets pushed around by the pressure of sunlight,” said Oscar Fuentes-Muñoz, a NASA postdoctoral fellow and co-author of the study. “That 2024 PT5 doesn’t move this way indicates it is much denser than [human-made] space debris.”
The team also noted a lack of space weathering on the asteroid’s surface, suggesting it hadn’t been exposed to the harsh environment of space for long — perhaps just a few thousand years. This further supported the idea that it was a relatively recent fragment of the Moon.
A Growing Family of Lunar Asteroids
2024 PT5 is only the second asteroid to be linked to the Moon. The first, 469219 Kamoʻoalewa, was identified in 2021 and is also thought to be a piece of lunar ejecta. Together, these discoveries suggest that there may be a hidden population of Moon fragments orbiting near Earth, waiting to be discovered.
“We knew that lunar ejecta were potentially hiding in these kinds of really near-Earth orbits,” Kareta told the NY Times. “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.”
If more of these lunar asteroids are found, they could help scientists piece together the Moon’s history. By tracing their origins to specific impact craters, researchers could learn more about the processes that shape the lunar surface.
For now, 2024 PT5 has moved on, continuing its journey around the Sun. But its brief visit has left a lasting impression, reminding us that even the smallest objects in space can tell big stories.
“It’s good to see the public interested in asteroids that aren’t going to kill us,” Kareta said. “What a pleasure.”
The findings appeared in the Astrophysical Journal Letters.
