Discovery
Hawaii-based telescope detects tiny 'quasi-moon' orbiting Earth
The small asteroid has been orbiting the earth for decades but had escaped detection until recently due to unfavorable visibility windows.
![Newly discovered quasi-moon 2025 PN7 shares a similar orbit with Earth. [NASA]](/gc8/images/2025/10/15/52320-2025-pn7-nasa-370_237.webp)
By Sarah Cope |
Astronomers recently announced the discovery of a new quasi-moon, designated 2025 PN7. Quasi-moons are asteroids that orbit the sun in a pattern so similar to that of our planet they appear to be orbiting Earth, like our moon.
The asteroid was first detected August 2 by the Hawaii-based Pan-STARRS1 (Panoramic Survey Telescope and Rapid Response System) and classified in September after its orbit was identified.
The paths of quasi-moons, also known as Arjunas, are shaped by a resonance with Earth’s orbit. Viewed from Earth, they seem to be conducting a looping circuit around our planet.
Unlike our moon, which is gravitationally bound to Earth, quasi-moons maintain a delicate balance between solar and terrestrial influence, tracing elongated paths that keep them nearby for decades or centuries before drifting away.
![The University of Hawaii's Pan-STARRS Observatory is a 1.8-meter telescope located at the summit of Haleakalā, on Maui, Hawaii. [R. Ratkowski]](/gc8/images/2025/10/15/52317-pan-starrs-observatory-370_237.webp)
The newly identified quasi-moon is small and faint, estimated to measure about 19 meters across. Its size places it at the lower end of objects that can be reliably tracked, which helps explain why it eluded earlier observation.
Researchers believe 2025 PN7 has been orbiting Earth for the last 60 years. Yet its geometry relative to Earth and the sun made it difficult to detect, leaving it hidden until the Pan-STARRS survey captured enough data to model its orbit.
2025 PN7 is one of only a handful of quasi-moons discovered, according to Science X.
Just six others have been identified to date, including 469219 Kamoʻoalewa, discovered in 2016, which is thought to be an ancient lunar fragment, according to CNN.
Another quasi-moon, 2006 RH120, briefly accompanied Earth before moving on to another part of its orbit around the sun.
Quasi-moons provide astronomers opportunities to study orbital dynamics in the Earth-sun system, as well as the long-term behavior of small near-Earth objects.
They are distinct from "mini-moons," or temporary captured objects (TCOs), which enter Earth’s gravity well for a limited period before escaping.
Unlike those transient visitors, a quasi-moon does not circle Earth directly.
Instead, it maintains a synchronized solar orbit that allows it to remain near Earth’s path -- in the case of 2025 PN7, for an anticipated 128 years.
The distinction between different types of orbital objects underscores the complexity of orbital mechanics, where resonance, gravitational perturbations, and relative velocities all combine to produce stable but unusual trajectories.
Tracking near-Earth objects
The discovery of 2025 PN7 contributes to ongoing efforts to track near-Earth objects of all sizes.
Large asteroids have been the focus of planetary defense initiatives, but smaller objects remain difficult to observe despite their potential to enter the atmosphere.
A body of 19 meters, if it were to collide with Earth, would not cause catastrophic damage but could produce a significant airburst.
This happened on February 15, 2013, when an asteroid exploded above Chelyabinsk, Russia, according to the Planetary Society.
Quasi-moons are seen as candidates for future exploration, as their proximity and predictable orbits could make them accessible targets for robotic missions.
China's Tianwen 2 probe, which departed in May, plans to study 469219 Kamoʻoalewa up close and take samples of the quasi-moon when it reaches it in July 2026, according to Space.com.
Sample-return efforts from small bodies have advanced planetary science already, and quasi-moons may offer opportunities to extend that research.
The identification of 2025 PN7 highlights the continued value of wide-field observatories like Pan-STARRS, developed and operated by the University of Hawaii's Institute for Astronomy, which operates telescopes on Maui.
Pan-STARRS is one of the leading discoverers of Near-Earth Objects (NEOs) and newly identified comets.
By scanning large swaths of the sky, it detects faint moving objects that would otherwise escape notice, offering astronomers opportunities to analyze orbital relationships and celestial bodies.