A tiny “quasi-moon” called Kamoʻoalewa shadows Earth’s orbit and may be a piece of the actual Moon blasted into space by an ancient impact — and China’s Tianwen-2 spacecraft is now closing in to bring a sample back to Earth.

Earth has one Moon, but it does not travel entirely alone. A small asteroid called Kamoʻoalewa loops along beside our planet as a “quasi-moon,” and there is real evidence that it may be a fragment of the actual Moon, flung into space by an ancient impact. China’s Tianwen-2 spacecraft has now reached it and is preparing to bring a piece of it home.

Two parts of that description are settled. Kamoʻoalewa genuinely is a quasi-moon of Earth, and a spacecraft genuinely is now alongside it. The lunar origin is the intriguing part that is not yet proven, which is exactly why the sample matters.

A companion that is not quite a moon

Kamoʻoalewa was discovered in 2016 by the Pan-STARRS survey telescope on Haleakala in Hawaii, which is where its Hawaiian name comes from. It is small, somewhere in the range of 40 to 100 metres across, closer to the size of a large building than a world.

It is called a quasi-moon because of the odd path it traces. It does not orbit the Earth the way the Moon does. Instead it orbits the Sun on a track so similar to our own, taking about a year to go around, that from Earth’s point of view it appears to make slow loops around us as the two of us travel along together. It is not gravitationally bound to Earth and could drift away over long timescales, but for now it is the steadiest of the seven known quasi-moons of Earth, and it is expected to keep pace with us for centuries. It also spins quickly, turning once every 28 minutes or so.

The clue in its colour

The reason anyone suspects a lunar origin is the way Kamoʻoalewa reflects sunlight. In 2021, a team led by Ben Sharkey, then at the University of Arizona, used the Large Binocular Telescope to measure its spectrum and found that it did not look like a normal near-Earth asteroid. Instead it closely matched weathered silicate rock from the Moon, the kind of material returned by past lunar missions.

That raised an obvious possibility: that Kamoʻoalewa is a piece of the Moon itself, blasted off by a meteorite strike and left in an orbit near Earth. Later modelling work pointed to a specific culprit, a relatively young crater on the Moon’s far side called Giordano Bruno, about 22 kilometres wide and thought to have formed within the last several million years. More recent studies have argued that a different crater, Tycho, fits the evidence better.

This is where caution is needed. A spectral match is a strong hint, not a verdict. It is drawn from reflected light rather than from the rock itself, and some researchers still argue that Kamoʻoalewa came from the main asteroid belt and merely drifted into its current orbit. The lunar story is the leading idea, but it remains a hypothesis.

Why a sample would settle it

Reflected light can only reveal so much. A physical sample, examined in a laboratory, would show the object’s exact minerals and isotopic makeup, the chemical fingerprints that separate lunar rock from ordinary asteroid material. If the sample matches the Moon, the case is effectively closed. If it looks like a common asteroid, the lunar idea falls away. Either result would be worth having, which is much of why the object was chosen as a target in the first place.

China’s Tianwen-2 arrives

Tianwen-2, run by the China National Space Administration, launched on 28 May 2025 and spent about 13 months crossing to its target. It reached Kamoʻoalewa around 7 June 2026. The space agency was slow to confirm the arrival officially, but radio astronomers in Germany and the Netherlands, tracking the spacecraft’s signal, independently confirmed that the rendezvous manoeuvre had taken place.

Having arrived a couple of thousand kilometres out, the spacecraft is now closing the final distance, working its way in to within a few tens of kilometres so that it can begin mapping the asteroid with cameras, laser ranging and radar. The first close-up images are expected soon after it settles into its survey orbit.

The hard part is grabbing a piece

Collecting the sample will not be simple. That 28-minute spin makes the surface a fast-moving target, and no one yet knows whether it is solid rock or loose rubble. To improve the odds, Tianwen-2 carries more than one sampling method, including a quick touch-and-go, an anchor-and-attach approach, and a technique in which the craft matches the asteroid’s rotation and reaches in with a robotic arm. The aim is to gather at least a few hundred grams of material. The rapid spin is itself a clue, because bodies that turn this fast tend to be single solid lumps rather than loosely bound piles of gravel.

What to watch

The plan is for Tianwen-2 to study the asteroid into 2027, then depart around 24 April 2027, which is China’s national space day, and send its sample capsule down over Inner Mongolia later that year. Success would make it China’s first asteroid sample return, and only the fourth from any asteroid, after Japan’s two Hayabusa missions and NASA’s OSIRIS-REx. The spacecraft would not stop there. After dropping the capsule it is set to swing past Earth and use the planet’s gravity to fling itself toward a distant target in the main asteroid belt.

The things to watch in the meantime are concrete. Whether the first detailed images arrive on schedule, whether the sampling attempt succeeds against that fast spin, and, in the end, whether the rock in the laboratory turns out to carry the fingerprint of the Moon. Only then will we know whether Earth has been quietly shadowed, all this time, by a piece of its own satellite.