A quasi-moon is an asteroid that orbits the Sun in almost exactly the same amount of time as a planet, causing it to appear to loop around that planet like a satellite. But unlike a true moon, it isn’t gravitationally bound to the planet at all. It’s bound to the Sun. Earth currently has seven known quasi-moons, the most studied being a small rocky body called Kamoʻoalewa, which may actually be a chunk of our own Moon blasted into space by an ancient impact.
How a Quasi-Moon Orbit Works
Every planet exerts a gravitational pull on nearby objects, but a quasi-moon never falls under that control. Instead, it circles the Sun on its own independent path that happens to take the same amount of time as the planet’s orbit. Because both the planet and the asteroid complete one trip around the Sun in roughly the same period, they stay near each other year after year. Astronomers call this a 1:1 mean-motion resonance.
From the planet’s perspective, the quasi-moon traces a slow, oblong loop that makes it look like it’s circling the planet. But that’s an illusion created by the shared orbital timing. If you could watch from above the solar system, you’d see two objects independently orbiting the Sun on slightly different paths, drifting closer and farther apart in a repeating pattern. The quasi-moon never settles into a stable circle around the planet the way our Moon does.
This type of orbit isn’t permanent, either. Quasi-moons can transition into other co-orbital arrangements over time. There are three main types of co-orbital motion: Trojan orbits, where an asteroid sits near a stable point 60 degrees ahead of or behind a planet; horseshoe orbits, where an object traces a wide arc along the planet’s orbital path; and quasi-satellite orbits, where the object stays in the planet’s general neighborhood. An asteroid can shift between horseshoe and quasi-satellite motion and back again over thousands of years as gravitational nudges accumulate.
How Quasi-Moons Differ From True Moons
The distinction comes down to which object holds the gravitational leash. A true moon orbits a planet, held in place by the planet’s gravity within a region called the Hill sphere. Our Moon, for example, is firmly locked to Earth and travels with it through space. A quasi-moon orbits the Sun, not the planet. It simply shares a similar orbital period, which keeps it loosely associated with the planet but never captured by it.
This means quasi-moons are far less stable companions. They drift in and out of their quasi-satellite configuration over centuries or millennia, sometimes wandering millions of kilometers away before looping back. One of Earth’s quasi-moons, known as 2023 FW13, has been in Earth’s vicinity since roughly 100 B.C. and is expected to stick around until at least A.D. 3700. That’s a long time by human standards but a blink compared to our actual Moon, which has orbited Earth for over four billion years.
Earth’s Known Quasi-Moons
As of mid-2025, astronomers have identified seven quasi-moons associated with Earth. The most famous is 469219 Kamoʻoalewa, first spotted in 2016 by the Pan-STARRS observatory in Hawaii. Others include one named Cardea, along with 2023 FW13 and the most recently discovered, 2025 PN7, found on August 29, 2025.
These are small objects. The newest, 2025 PN7, is roughly 20 meters (66 feet) wide. Kamoʻoalewa is estimated to be in a similar size range. For comparison, Earth’s actual Moon is about 3,474 kilometers across. Quasi-moons are essentially tiny asteroids that happen to share our orbital neighborhood, and they’re so faint that discovering them requires powerful survey telescopes scanning the sky repeatedly.
Kamoʻoalewa: A Piece of the Moon?
Kamoʻoalewa stands out among Earth’s quasi-moons because its surface doesn’t look like a typical asteroid. When astronomers analyzed the light reflected off its surface across a wide range of wavelengths, they found a composition rich in silicate minerals with an unusually reddened spectrum. That reddening is a signature of extreme space weathering, the slow bombardment by solar wind and micrometeorites that darkens and reddens a rocky surface over time.
The closest match for Kamoʻoalewa’s spectrum isn’t any common asteroid type. It’s lunar soil. The reflectance pattern aligns better with Moon samples than with the silicate asteroids that make up most of the near-Earth population. This has led researchers to propose that Kamoʻoalewa is a fragment of the Moon, launched into space by a large impact on the lunar surface. If true, it would mean a piece of our Moon has been quietly looping around Earth’s orbit for an unknown stretch of time.
Kamoʻoalewa also spins fast, completing one rotation roughly every 28 minutes. That rapid spin is consistent with a small, solid fragment rather than a loosely held rubble pile, which would fly apart at that speed.
A Mission to Visit One
China’s Tianwen-2 mission aims to settle the question of Kamoʻoalewa’s origin by visiting it directly. The spacecraft is designed to collect samples from the asteroid’s surface and return them to Earth about 2.5 years after launch. If those samples confirm a lunar composition, it would provide direct evidence of a major impact event on the Moon and offer a natural laboratory for studying how ejected material behaves after a collision.
Planetary scientists Li Chunlai and Liu Jianjun of China’s National Astronomical Observatories have described Kamoʻoalewa’s unique orbit, unknown origin, and undetermined characteristics as making it “highly valuable for scientific exploration.” The mission could answer broader questions about how quasi-satellites form and how their orbits evolve over time. After releasing its sample return capsule, the Tianwen-2 probe will continue on to comet 311P/PANSTARRS, arriving about seven years later to study clues about the early solar system, including whether comets delivered water and organic building blocks to Earth.
Even if Kamoʻoalewa turns out not to be lunar material, the samples would still represent the first laboratory analysis of a quasi-moon, giving scientists a close look at one of Earth’s most unusual neighbors.