Earth’s Recent Mini-Moon Has Lunar Origin, New Study Suggests

The near-Earth asteroid 2024 PT5 is on an Earth-like orbit that remained in the immediate vicinity of our planet for several months at the end of 2024.

2024 PT was first detected on August 7, 2024, by the NASA-funded Sutherland, South Africa, telescope of the University of Hawai’i’s Asteroid Terrestrial-impact Last Alert System (ATLAS).

The asteroid does not pose a hazard to Earth, but its orbit around the Sun closely matches that of our planet.

About 10 m (33 feet) wide, the object appears to be composed of rock broken off from the Moon’s surface and ejected into space after a large impact.

“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,” said Dr. Teddy Kareta, an astronomer at Lowell Observatory.

“It looks like it hasn’t been in space for very long, maybe just a few thousand years or so, as there’s a lack of space weathering that would have caused its spectrum to redden.”

Dr. Kareta and his colleagues used observations from the Lowell Discovery Telescope and the NASA Infrared Telescope Facility (IRTF) at the Mauna Kea Observatory in Hawai’i to show that the spectrum of reflected sunlight from the surface of 2024 PT didn’t match that of any known asteroid type. Instead, the reflected light more closely matched lunar rocks.

This discovery doubles the number of known asteroids thought to originate from the Moon.

“Asteroid 469219 Kamo’oalewa was found in 2016 with an Earth-like orbit around the Sun, indicating that it may also have been ejected from the lunar surface after a large impact,” the astronomers said.

“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.”

“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.”

“Also, material from deep below the lunar surface — in the form of asteroids passing close to Earth — may be accessible to future scientists to study.”

“This is a story about the Moon as told by asteroid scientists,” Dr. Kareta said.

“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.”

The findings were published January 14, 2025 in the Astrophysical Journal Letters.

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Theodore Kareta et al. 2025. On the Lunar Origin of Near-Earth Asteroid 2024 PT5. ApJL 979, L8; doi: 10.3847/2041-8213/ad9ea8