The new temporary satellite of Earth turned out to be a fragment of the Moon.

Sometimes, Earth can capture small near-Earth asteroids with its gravity. This occurs when such objects are located close enough to our planet (within the Hill sphere) and pass by at a suitable speed, allowing Earth's gravity to alter their orbit. Scientists refer to these bodies as “mini-moons”. They can become either quasi-satellites, capable of remaining in orbit for centuries, or temporary satellites, staying near the planet for several hours to several days or even months.

The majority of “captured” near-Earth asteroids are too small to pose a threat to humans. However, they are convenient targets for scientists, as they are closer than other near-Earth objects.

During astronomical observations, researchers have discovered dozens of temporary satellites of Earth. Among the latest is 2024 PT5, which has a diameter of 10-11 meters and was detected in August 2024 thanks to the ground-based telescope system ATLAS. It remained in the status of a temporary satellite for 56 days, from September to November, and will only regain that status in 2055.

Initial observations indicated that 2024 PT5 is likely a representative of the near-Earth asteroid family Arjuna, whose orbits are very similar to Earth's in nature, exhibiting low inclination and orbital periods close to one year.

A team of astronomers from the USA, led by Teddy Kareta from the Lowell Observatory in Arizona, re-studied 2024 PT5 and found that its appearance is unlike most other known near-Earth asteroids. This research was discussed in a paper published on the electronic preprint archive arXiv.org.

The chemical composition of 2024 PT5 is similar to that of lunar rock samples collected by the Apollo 14 mission in 1971. Furthermore, the solar radiation pressure observed on the asteroid's trajectory is significantly lower than would be expected for an artificial object. Therefore, it is highly likely that 2024 PT5 is not an artificial object or a cosmic wanderer formed in the outskirts of the Solar System, but rather a piece of the Moon—a rock that broke off from the surface of our natural satellite as a result of a collision with a large body.

Kareta and his colleagues studied the reflection spectrum of 2024 PT5 using two ground-based telescopes: the Lowell Discovery Telescope and NASA's IRTF infrared telescope located on the summit of Mauna Kea volcano in Hawaii. The scientists concluded that the asteroid's composition is rich in pyroxene—a mineral commonly found on the Moon, typically found in basaltic rocks formed from lava in the lunar maria.

For instance, pyroxene is abundant in samples collected by astronauts Alan Shepard and Edgar Mitchell on the near side of the Moon in the Fra Mauro formation—a hilly area believed to be composed of ejecta. This means it consists of material that originated from depth but was ejected to the surface as a result of an impact event.

“The astronauts primarily collected samples from the highlands—brighter regions of the Moon visible from Earth. We hypothesize that relatively recently—perhaps 200,000 years ago—something large collided with this region and ejected lunar rocks into space, including 2024 PT5. If asked which part of the Moon this asteroid originated from, I would say from the highlands,” explained Kareta.

If 2024 PT5 is indeed a fragment of lunar rock, it will be the second known asteroid formed in this way. In 2021, a group of astronomers concluded that a previously discovered small near-Earth asteroid (469219) Kamo`oalewa was ejected from the Moon's surface. Its spectra resemble those of lunar soil samples returned by the Apollo 14 and Luna 24 missions. Specifically, studies of the reflected light spectrum showed that the asteroid's chemical composition is reminiscent of the mineral anorthosite—the primary component of the lunar crust.

In 2025, China plans to send the “Tianwen-2” mission to the near-Earth asteroid (469219) Kamo`oalewa to return samples of its soil. If the mission is successful, scientists will have valuable material that will shed light not only on the composition and origin of these objects but also help better understand the processes of lunar formation and the interactions between Earth and its satellite.

According to the researchers who made the discovery, there may be around 16 near-Earth asteroids near our planet that originated from lunar rocks. However, detecting them is quite challenging because they are small and very faint.

Other researchers believe that such objects are unlikely to be encountered too frequently, as “the right conditions” are required for their formation. If insufficient energy is released during a collision with the lunar surface, the resulting fragments will simply fall back to the surface. Conversely, if too much energy is released, the fragments will overcome the Moon's gravity and escape the gravitational influence of the Earth-Moon system.