A New Celestial Neighbor in Earth’s Orbit
Astronomers have made a groundbreaking discovery in our solar system, identifying a previously unknown quasi-moon that has been orbiting near Earth for decades. This small celestial object, designated as 2025 PN7, is an asteroid that follows a path around the sun but maintains a close proximity to our planet. Unlike temporary mini-moons that occasionally orbit Earth, 2025 PN7 has likely been in an Earth-like orbit for about 60 years without being detected by telescopes.
The discovery of 2025 PN7 was made possible through observations captured by the Pan-STARRS observatory located on the Haleakala volcano in Hawaii. Archival data revealed that the object has been in an Earth-like orbit for decades, suggesting that it has been a silent companion to our planet for a significant period.
Understanding Quasi-Moons
Quasi-moons are a unique category of near-Earth asteroids that orbit the sun but remain in close proximity to Earth. These objects differ from temporary mini-moons, such as 2024 PT5, which circled the planet for two months in 2024 and could be an ancient fragment blasted off from our moon. 2025 PN7 is one of a handful of known quasi-moons, including Kamo‘oalewa, which is also thought to be an ancient lunar fragment. Kamo‘oalewa is a destination for China’s Tianwen-2 mission, which aims to collect and return samples from the space rock in 2027.
The research on 2025 PN7 was published in the journal Research Notes of the American Astronomical Society on September 2. The paper was authored by Carlos de la Fuente Marcos, a researcher at the Complutense University of Madrid. He explained that the space rock has managed to escape the notice of astronomers for so long due to its small size and faintness.
Characteristics of 2025 PN7
The asteroid 2025 PN7 swings within 186,000 miles (299,337 kilometers) of Earth during its closest pass, according to de la Fuente Marcos. On average, it is 238,855 miles (384,400 kilometers) away from Earth, according to NASA. The space rock can only be detected by currently available telescopes when it gets close to our planet, as its visibility windows are few and far between.
De la Fuente Marcos noted that finding and studying quasi-moons can reveal more about our corner of the universe. He emphasized that the Solar System is full of surprises, and the existence of 2025 PN7 suggests that there may not exist a lower limit to the size of a quasi-satellite.
Size and Orbit of 2025 PN7
Astronomers are still trying to determine the exact size of 2025 PN7. A reasonable estimate is about 98 feet (30 meters) across, with the potential to be 62 feet (19 meters) in diameter, according to EarthSky. The space rock is currently the smallest-known quasi-moon to have orbited near Earth.
Over time, 2025 PN7 switches between a closer, more circular Earth-like orbit and a horseshoe orbit, similar to Kamoʻoalewa’s. During the horseshoe orbit, the space rock can reach a distance of 185 million miles (297 million kilometers) from Earth. The quasi-moon is expected to remain in its current near-Earth orbit for about another 60 years before the gravitational tug of the sun pulls it back into a horseshoe orbit.
Composition and Origin
Questions remain about the composition of 2025 PN7, which is currently unknown. Based on what little is known so far, it is almost certainly a rocky and natural object. Dr. Teddy Kareta, assistant professor in the department of astrophysics and planetary science at Villanova University, explained that while some old satellites and rocket junk end up in these very-near-Earth kinds of orbits, it is often possible to distinguish between natural and artificial objects based on how their orbits evolve on short timescales.
Kareta, who has studied mini-moons and quasi-moons, was not involved in the research and mentioned that bad weather has interfered with his plans to observe 2025 PN7.
Possible Lunar Origins
While 2025 PN7, like Kamoʻoalewa, may also be a piece of the moon, more data is needed to confirm this, according to de la Fuente Marcos. He believes that 2025 PN7 came from the Arjuna asteroid belt. Unlike the main asteroid belt, located between the orbits of Mars and Jupiter, the Arjuna asteroid is not a distinct belt. Instead, they are a group of small space rocks that have orbits around the sun similar to Earth’s.
Previously, de la Fuente Marcos had proposed that mini-moon 2024 PT5 was also an Arjuna asteroid that could have come from Earth’s moon before becoming part of the belt. He now believes that material ejected during lunar impacts may contribute members to the Arjuna secondary asteroid belt.
Impact Risk and Future Exploration
Even though quasi-moons and mini-moons can closely approach our planet, they don’t typically pose an impact risk for Earth, according to de la Fuente Marcos. Therefore, 2025 PN7 is no threat. Sending missions to investigate quasi-moons, as Tianwen-2 is expected to do with Kamoʻoalewa, could reveal the true origin and history of these intriguing space rocks.
“These asteroids are relatively easy to access for unmanned missions and can be used to test planetary exploration technologies with a relatively modest investment,” de la Fuente Marcos said. Such missions could provide valuable insights into the origins of these celestial objects and the broader dynamics of our solar system.
