Our home planet, Earth, appears to be a solitary haven in our solar system. Yet, we’re far from truly alone, constantly receiving visits from celestial wanderers, most notably asteroids. While often harmless, some of these rocky guests decide to linger, adopting a temporary, moon-like role.
The latest addition to this cosmic entourage is an asteroid officially named 2025 PN7. Discovered just this summer, it remarkably mirrors Earth’s path around the sun. Imagine our planet as a car cruising in a highway lane; 2025 PN7 is driving right beside us! This phenomenon earns it the classification of a ‘quasi-moon.’ What makes this particular discovery even more fascinating is its diminutive size – possibly less than 52 feet long, making it potentially the smallest quasi-moon ever observed. To put that into perspective, it’s shorter than a standard bowling lane!
Where do these space rocks come from? Some asteroids orbiting Earth originate from the vast main asteroid belt nestled between Mars and Jupiter. Others are fragments of our own moon, flung into space by powerful meteorite impacts. Given the limited telescopic observations of 2025 PN7 so far, its exact origins remain a mystery, open only to speculation, as noted by Carlos de la Fuente Marcos, an astronomer at the Complutense University of Madrid and a co-author of the study announcing this discovery in the journal Research Notes of the American Astronomical Society.
However, one fact about this asteroid is clear: its visit is strictly temporary.
2025 PN7 is part of a small, intriguing group of space rocks that either briefly follow, precede, or journey alongside Earth in its solar orbit. Like its fellow travelers, this asteroid will eventually drift away, continuing its voyage through the cosmos, likely within the next 60 years.
Earth actually hosts several such celestial companions, including both ‘mini-moons’ and ‘quasi-moons.’ Mini-moons are transient objects that truly orbit our planet, but their loyalty is short-lived, usually lasting only a few months. A recent example was 2024 PT5, which joined us last autumn before gracefully departing by the end of November.
To visualize its journey, imagine 2025 PN7 gracefully orbiting Earth, a dance captured in simulations that predict its eventual departure in about 60 years.
In contrast to mini-moons, quasi-moons don’t orbit Earth directly; they orbit the sun, maintaining a synced relationship with our planet’s path. These are far more persistent companions, sometimes staying locked in Earth’s orbital embrace for hundreds or even thousands of years. Their prolonged proximity makes them prime candidates for scientific exploration. For instance, another quasi-moon, Kamoʻoalewa, is the target of China’s Tianwen-2 mission, which aims to collect and bring back a geological sample for in-depth study.
Astronomers first caught sight of 2025 PN7 on August 2, using the Pan-STARRS observatory at the University of Hawaii. Subsequent examination of archival images revealed its presence extending back several years, enabling scientists to precisely map its unique orbit.
Interestingly, 2025 PN7 appears to have settled into its quasi-moon orbit around 1957 — just in time to witness humanity’s pioneering step into space with the launch of Sputnik 1, Earth’s very first artificial satellite.
According to astronomical estimations, 2025 PN7 made its closest approach to Earth in August 1980, coming within 2.5 million miles – a distance approximately ten times greater than that between Earth and our familiar moon. At its furthest point, this quasi-moon may venture as far as 11 million miles away.
Current simulations suggest that 2025 PN7 will remain in Earth’s orbital vicinity for an impressive 126 years. However, its ‘quasi-moon’ designation will cease in 2083, when it finally breaks away.
The title of ‘tiniest quasi-moon’ for 2025 PN7 is still provisional. Astronomers typically gauge an asteroid’s size by observing how much sunlight its surface reflects. However, 2025 PN7 has proven elusive, making its surface properties, and thus its true dimensions, hard to ascertain. Dr. de la Fuente Marcos admits, “We cannot really tell its true size.” It could potentially be as large as 160 feet. Future observations, whenever possible, will be crucial in confirming whether it retains its claim as the smallest known quasi-moon.
Regardless of its exact size, the discovery of 2025 PN7 is a welcome event. Near-Earth asteroids, particularly those not posing a threat of collision, offer invaluable insights into the formation and evolution of our inner solar system.
As Federica Spoto, an asteroid dynamics researcher at the Harvard-Smithsonian Center for Astrophysics, who was not part of this study, aptly puts it: “It is even cooler when they get captured and they stay close to the Earth for quite some time.”