Astronomers have identified a new quasilunar moon, designated 2025 PN7, which is the seventh confirmed object of its kind to accompany Earth. This small Apollo-type asteroid was detected in August by the Pan-STARRS 1 telescope in Hawaii, primarily through its brightness.
Upon analyzing its trajectory, researchers determined that 2025 PN7 maintains a 1:1 resonance with Earth, meaning it orbits the sun simultaneously with our planet. This alignment creates the illusion that Earth is accompanied by an additional moon, even though quasilunar moons like 2025 PN7 are not gravitationally tethered to Earth. Rather, they are transient companions that follow their own solar orbit. At its closest approach, 2025 PN7 comes within 299,000 kilometers of Earth, while its farthest distance can reach up to 17 million kilometers. For context, the actual moon orbits Earth at an average distance of approximately 384,000 kilometers.
According to a study published in the Research Notes of the AAS, 2025 PN7 has been in its current quasi-satellite phase since 1965 and is expected to continue in this state for 128 years. Some scientists project that it will drift away from this phase by 2083.
So far, seven bodies have been confirmed as quasilunar moons orbiting in tandem with Earth. Researchers believe that additional quasilunar moons may be discovered in the future. Earth serves as a natural reservoir for these celestial bodies due to its orbital dynamics, which resemble those of certain nearby objects in the Arjuna group of asteroids. This group, recently subjected to more detailed study, consists of near-Earth rocks that share similar orbits with our planet.
Unlike the asteroid belt found between Mars and Jupiter, the Arjuna group does not form a ring structure. Instead, it comprises a collection of asteroids that occasionally intersect with Earth”s orbit. Depending on their orbital characteristics, these objects may be classified as quasilunar moons or mini-moons. The distinction lies in their behavior: quasilunar moons orbit the sun together with Earth, while mini-moons typically engage in horseshoe-like orbital motions around Earth and only appear for brief periods, lasting weeks or months.
The seven known quasilunar moons, all part of the Arjuna group, include 164207 Cardea, 277810, 2013 LX28, 2014 OL339, 469219 Kamoʻoalewa, 2023 FW13, and now 2025 PN7. The Pan-STARRS observatory has established itself as a leading facility for detecting near-Earth objects, contributing to the discovery of quasilunar moons, comets, and even supernovae. This is made possible by its advanced 1.4 billion pixel digital camera, recognized as the largest of its kind globally.
In the realm of astronomy, the formation of moons can occur through various mechanisms. Some planets, such as Jupiter and Saturn, capture nearby celestial bodies, while Earth”s satellites originated from collisions during the early history of the solar system. A crucial criterion for an object to be classified as a true moon is that it must be permanently bound by the gravity of its parent planet.
