Astronomers Identify Small Quasi‑Moon 2025 PN7 That Likely Hid in Near‑Earth Space for Decades
62‑foot asteroid appears to be a temporary quasi‑satellite of Earth, researchers report in Research Notes of the American Astronomical Society
Astronomers report the discovery of a tiny quasi‑moon of Earth, an asteroid designated 2025 PN7 that appears to have shared Earth's neighborhood for decades while remaining largely undetected.
The object, measured at about 62 feet (19 meters) across, was described in a study published Sept. 2 in Research Notes of the American Astronomical Society. Lead author Carlos de la Fuente Marcos of the Complutense University of Madrid called 2025 PN7 "the smallest and the least stable known quasi‑satellite of Earth." French journalist Adrien Coffinet first publicized the object Aug. 30 on the Minor Planet Mailing List after calculating that it would behave as a quasi‑satellite of Earth for about the next 60 years, based on observations made July 30 with the Haleakalā Observatory's Pan‑STARRS1 telescope in Maui, Hawaii.
Quasi‑moons, sometimes called quasi‑satellites, do not orbit Earth the way the moon does. Instead, they orbit the sun in a path that keeps them in a 1:1 orbital resonance with Earth, appearing from a terrestrial vantage point to trace looped or kidney‑shaped tracks relative to the planet. The Planetary Society has cataloged a small number of such co‑orbital companions; 2025 PN7 joins a handful of previously identified quasi‑satellites that can be described as a "gravitational sleight of hand." De la Fuente Marcos and others said the object’s small size and faintness make it visible only with high‑quality telescopes during narrow observation windows, accounting for why it likely escaped detection for so long.
De la Fuente Marcos told Live Science that 2025 PN7’s limited brightness and unfavorable visibility windows make it unsurprising that it remained unnoticed. Coffinet’s calculations, which drew on Pan‑STARRS1 data, indicate the object will maintain a quasi‑satellite configuration with Earth for roughly six decades before dynamical interactions change its orbit.
The discovery process reflects the growing role of survey telescopes and amateur and professional collaboration in finding near‑Earth objects. Pan‑STARRS1, operated by the University of Hawai‘i, routinely scans the sky for faint moving objects; follow‑up analyses and orbital integrations by researchers and community observers refine assessments of how such bodies move relative to Earth.
Scientists classify quasi‑satellites differently from temporarily captured natural satellites, sometimes called minimoons, which can enter brief bound orbits around Earth. 2025 PN7’s trajectory indicates it is a co‑orbital asteroid rather than a true moon: it is bound primarily to the sun but remains in a relative configuration with Earth for an extended interval. De la Fuente Marcos said such objects can be "full of surprises," and that more quasi‑moons could be identified as survey coverage and detection capabilities improve.
Because 2025 PN7 is small and currently on an orbit that keeps it near Earth only in a relative sense, researchers treating it as a quasi‑satellite do not characterize it as a long‑term or permanent moon and have not reported any immediate impact threat. The finding underscores both the dynamic structure of near‑Earth space and the limits of past surveys in detecting faint, small bodies whose orbital geometries produce infrequent favorable viewing windows.
The authors and other observers plan to continue monitoring 2025 PN7 to refine orbital predictions and to improve understanding of how such co‑orbital objects are captured into and released from quasi‑satellite states. Continued improvements in wide‑field surveys and follow‑up capabilities are expected to yield additional discoveries of small, transient companions in Earth’s orbital neighborhood.