Astronomers have confirmed the discovery of Earth’s seventh quasilunar moon, designated as 2025 PN7. This small Apollo-type asteroid was detected in August using the brightness measurements from the Pan-STARRS 1 telescope located in Hawaii. Analysis of its trajectory indicates that 2025 PN7 maintains a 1:1 resonance with Earth, meaning it orbits the sun simultaneously alongside our planet.
This unique synchronization gives the appearance of an additional moon accompanying Earth. Unlike traditional moons, quasilunar moons are not gravitationally tethered to our planet. They act as temporary companions, following their own paths around the sun. For 2025 PN7, its closest approach to Earth is at a distance of 299,000 km, while its farthest point can extend to 17 million km. In contrast, the moon orbits at an average distance of 384,000 km.
Characteristics and Future of 2025 PN7
According to findings published in the Research Notes of the AAS, 2025 PN7 has been in a quasi-satellite phase since 1965 and is expected to maintain this status for another 128 years. Researchers project that it will drift away from this phase by 2083.
This discovery adds to the growing list of bodies identified as quasilunar moons. Currently, there are seven known objects sharing this classification, all belonging to the Arjuna group of asteroids. This group comprises near-Earth rocks that orbit the sun similarly to Earth, leading to occasional close encounters. The classification of a body as a quasilunar moon depends on its orbital dynamics, distinguishing it from mini-moons, which exhibit different orbital behaviors.
Mini-moons orbit Earth in a horseshoe pattern and are typically visible for brief periods, lasting weeks or months before departing. In contrast, the seven confirmed quasilunar moons, including 164207 Cardea, 277810, 2013 LX28, 2014 OL339, 469219 Kamoʻoalewa, and 2023 FW13, share the characteristic 1:1 resonance with Earth.
The Role of Pan-STARRS in Asteroid Detection
The Pan-STARRS observatory has established itself as a leading facility in the detection of near-Earth objects. Equipped with a 1.4 billion pixel digital camera, the largest of its kind globally, it has contributed to the discovery of various quasilunar moons, comets, and even supernovae. This capability enhances our understanding of the celestial bodies that share our solar system.
Understanding how moons form is crucial in astronomy. Some planets, such as Jupiter and Saturn, capture nearby bodies, while others, like Earth, form their satellites through collisions in the early solar system. To be classified as a true moon, a satellite must be permanently bound by a planet’s gravity, a rule that differentiates traditional moons from quasilunar and mini-moons.
As research continues, astronomers anticipate the discovery of more quasilunar bodies, potentially expanding our knowledge of these fascinating celestial companions. Earth’s orbit, resembling that of certain nearby asteroids, positions it as a natural reservoir for quasilunar moons. The ongoing study of the Arjuna group will likely yield further insights into the dynamics of these unique objects.
