Earth often hosts small, transient companions in addition to its single large Moon. PN7, a building‑sized rock spotted by Pan‑STARRS, has shadowed Earth since the 1960s and joins at least six other known quasi‑moons—objects that orbit the Sun on looping paths that can appear to circle Earth. Mini‑moons are briefly captured by Earth’s gravity and are even harder to detect; only four have been observed. Improved telescopes and upcoming missions, including a planned sample‑return to Kamoʻoalewa, should clarify where these visitors come from.
Earth Has More 'Moons' Than You Think — Meet PN7 and the Solar System’s Quasi‑Moons
Earth often hosts small, transient companions in addition to its single large Moon. PN7, a building‑sized rock spotted by Pan‑STARRS, has shadowed Earth since the 1960s and joins at least six other known quasi‑moons—objects that orbit the Sun on looping paths that can appear to circle Earth. Mini‑moons are briefly captured by Earth’s gravity and are even harder to detect; only four have been observed. Improved telescopes and upcoming missions, including a planned sample‑return to Kamoʻoalewa, should clarify where these visitors come from.
09:59 PM, 11/13/2025Science
Earth Has More 'Moons' Than You Think
A small, mysterious rock roughly the size of a building has been traveling alongside Earth as both circle the Sun. Astronomers only recognized the object — now designated PN7 — this summer, but it has been shadowing our planet for decades in a configuration researchers call a quasi‑moon.
When Ben Sharkey, an astronomer at the University of Maryland, first learned of PN7, their reaction was simple: “Oh cool, another one.” PN7 is the latest example in a steady procession of tiny, moon‑like companions near Earth.
Quasi‑moons vs. mini‑moons
Quasi‑moons do not orbit Earth the way our Moon does. Instead, they orbit the Sun on looping paths that sometimes carry them ahead of Earth and sometimes behind it, producing the appearance that they are circling the planet. By contrast, mini‑moons are small objects that Earth temporarily captures into actual orbits before they escape again.
None of these compare to the Moon, Earth’s one enduring natural satellite. Quasi‑moons and mini‑moons are detectable only with powerful telescopes that can catch faint sunlight glinting off small, fast‑moving rocks. Still, each new discovery is a reminder that our immediate cosmic neighborhood is busier — and more dynamic — than it appears.
“They really make you reconsider a nice, orderly, static view of the solar system,” Sharkey says.
What we know about PN7 and other companions
PN7 was spotted by the Pan‑STARRS observatory in Hawaii in late August. Models suggest it synchronized with Earth’s motion sometime in the mid‑1960s and will likely drift into a different solar orbit around 2083. With PN7’s discovery, researchers now count at least seven known quasi‑moons for Earth, though many more probably remain undetected.
Observed quasi‑moons range in size from roughly 30 feet to about 1,000 feet; PN7 may be among the smallest. Some quasi‑moons, like Kamoʻoalewa (discovered by Pan‑STARRS in 2016), can remain in a quasi‑orbital dance with Earth for centuries—Kamoʻoalewa has been in such an arrangement for about a century and is expected to remain so for hundreds more.
Mini‑moons are even rarer in observations: astronomers have recorded only four so far. These captured rocks usually remain bound to Earth for less than a year because their orbits are highly unstable; the most recent mini‑moon, roughly the size of a school bus, left Earth’s vicinity after a few months.
“Most mini‑moons are quite small, like boulders,” says Grigori Fedorets, an astronomer at the University of Turku in Finland. While none are currently known to be orbiting Earth, Fedorets’ analysis predicts that a mini‑moon a few feet across is typically present at any given time, and other studies suggest there could be several similar boulders around Earth at once.
Where do they come from?
Researchers are still debating the origins of these transient companions. Possibilities include:
- Near‑Earth asteroids nudged inward from the main asteroid belt by Jupiter’s gravity.
- Fragments blasted from the Moon by impacts — some studies of Kamoʻoalewa found a composition more lunar‑like than typical asteroids.
- Survivors of an ancient population of near‑Earth objects formed during the solar system’s early, chaotic days.
Sharkey suggests the answer may be a combination of these sources: Earth's extra moons—past, present, and future—could have multiple origins.
Why this matters
Improved telescope technology is making tiny objects like PN7 visible. Upcoming facilities, especially the Vera C. Rubin Observatory, are expected to uncover many more such companions. There is also active spacecraft interest: a Chinese mission launched this spring is scheduled to reach Kamoʻoalewa next summer and plans to collect surface samples for return to Earth, which should help pin down its origin.
Studying quasi‑moons and mini‑moons is a modern exercise in celestial mechanics—the same field that reshaped humanity’s understanding of the cosmos centuries ago. While these small companions won’t trigger another Copernican revolution, they are vivid reminders that gravity continually reshapes the neighborhood right around our planet.
One likely constant remains: Earth cannot permanently capture a large, stable second moon without an encounter with a massive body, which is not possible in the solar system’s current state, Fedorets says. But transient travel companions like PN7 are probably common enough to provide an ongoing supply of close‑by targets for observation and study—little counterpoints to Earth’s cosmic solitude.