The Chinese spacecraft Tianwen-2 is approaching the asteroid Kamoʻoalewa, one of Earth's semi-satellites. It will attempt to collect samples from its surface and return them to the laboratory, where researchers can determine whether it is a rock dislodged from the moon or a regular asteroid whose surface has been altered by prolonged exposure to space.
The moon It is not the only natural object moving in space next to the Earth. How many Asteroids Small ones orbit the Sun in orbits very similar to Earth's, also completing one revolution around the Sun in about a year. From our perspective, they sometimes appear to accompany Earth, which is why they are called Semi-satellites.
One of the most intriguing objects in this group is asteroid 469219. Kamuawalwa (469219 Kamoʻoalewa). Its name originates in the Hawaiian language, and roughly means a celestial object that wobbles or moves from side to side — a description referring to its apparent path in Earth's sky.
Kamu'aluwa moves in a relatively stable orbit around the sun, similar to Earth's orbit. For years, researchers have suggested that it may not be a regular asteroid, but rather a fragment of the moon that was thrown into space by a large object hitting the moon's surface.
Now China is setting out to test the hypothesis more closely. The spacecraft Tianwen-2 (Tianwen-2), launched in May 2025, was sent to explore Kamua'aluwa, collect samples from it, and return them to Earth for laboratory analysis.
A semi-satellite is not a moon.
The term semi-satellite can be misleading. Kamua'alwe does not orbit the Earth like the Moon, and is not gravitationally bound to it.
The Moon orbits the Earth because Earth's gravity holds it in its orbit. Kamehameha, on the other hand, orbits the Sun. It orbits with a period very similar to Earth's, so both objects remain in the same general region of the solar system for long periods of time.
When viewed in relation to Earth, it appears to move around us in a wide, winding orbit. In fact, this is the result of the combination of its orbit around the Sun and the motion of the Earth.
There are currently eight objects known to be classified as quasi-satellites of Earth. Kamua'alwa is one of the most stable and interesting of them.
Despite its apparent proximity to Earth, it does not come very close to us. At its closest approach on December 27, 1923, it was about 12.44 million kilometers from Earth—more than 30 times the average distance between the Earth and the Moon.
According to long-term orbital calculations, Kamu'ualwa entered its current state as a semi-satellite about a century ago. In the future, its orbit will change, and by the end of May 2369 it is expected to move away from Earth to a distance equal to twice the distance between the Earth and the Sun.
A small, rapidly rotating asteroid
Kamua'aluwa is estimated to be about 30 to 60 meters in diameter. Although it is a small object, its unusual orbit and possible lunar origin have made it an important scientific target.
It also rotates very quickly: one rotation around its axis takes only about 28 minutes.
The rapid rotation has practical significance. The gravity of such a small asteroid is very weak, and its surface is moving rapidly relative to the spacecraft. This makes it difficult to approach it, stand above it, and touch it without being propelled back into space.
The spacecraft will first need to measure its shape, mass, gravitational field, direction of rotation, and surface structure, and only then will it be possible to choose an appropriate method and site for collecting samples.
Is this a fragment from the moon?
The hypothesis that Kamehameha was formed from the moon is based primarily on the way its surface absorbs and reflects light.
Researchers use spectroscopy to examine distant objects. Each material absorbs and reflects wavelengths slightly differently, so the spectrum of the reflected light can provide information about the minerals and materials on the object's surface.
Early observations showed that Kamua'aluwa's spectrum was somewhat similar to that of lunar rock samples, leading to the suggestion that a meteorite or asteroid impact with the Moon hurled a rock at a speed high enough to overcome the Moon's gravity and enter orbit around the Sun.
If the hypothesis is correct, Kamua'alwa may be one of the rare fragments that was dislodged from the surface of the Moon and reached an orbit similar to Earth's.
This has broad scientific significance. Identifying a lunar fragment in space could teach us how large impacts eject material from the moon, how material moves inEarth-Moon system And how it reaches orbits around the sun.
It may be a normal rocky asteroid.
Not all researchers are convinced that Kamua'aluwa originated on the Moon. More recent analyses suggest that it may be a rocky asteroid of the LL chondrite type.
Chondrites are ancient rocky meteorites that represent material left over from the early stages of the formation of the Solar System. Type LL chondrites contain relatively low amounts of metallic iron and other metals.
According to this possibility, Kamu'aluwa originally came from a normal asteroid population, but its surface has undergone severe space weathering. Prolonged exposure to solar radiation, the solar wind, and tiny particle impacts has altered its color and spectrum, making it appear more like a lunar rock than it actually is.
The debate illustrates the limitations of remote observation. Telescopes can only measure the light reflected from the outermost layer of an object. If that layer has changed greatly, it could hide the original composition beneath.
Why does space weathering make identification difficult?
Objects without atmospheres, such as asteroids and the Moon, are directly exposed to the space environment.
The solar wind—a stream of charged particles emitted from the sun—is constantly hitting the surface. This is accompanied by high-energy radiation and impacts from tiny dust particles moving at high speeds.
These processes gradually change the structure and composition of the outer layer. They can darken the surface, change its color, and change the way it reflects light.
As a result, two rocks of different origins may look similar after long periods in space. Likewise, rocks of similar origins may look different if they have undergone different weathering conditions.
Therefore, a sample taken from below the outer layer can be very valuable. Subsurface material may be better preserved and better reflect the original composition of the asteroid.
Tianwen-2 set out to bring samples
The China National Space Administration launched Tianwen-2 in May 2025. It is an ambitious mission that combines close-up observation, sample collection, and return to Earth.
Observations made from a ground station in Bochum, Germany, indicated that the spacecraft performed several short engine firings and then a major maneuver on June 7, 2026.
Based on ground-based tracking, the spacecraft has reached the vicinity of Kamu'aluwa and may have already entered an operational orbit near it. As of press time, the main science phase was expected to begin in the first week of July 2026. However, a detailed official report from the Chinese authorities on the mission status and the start of sampling operations must be awaited.
The mission is particularly challenging because of the asteroid's small size and rapid rotation. Unlike landing on a planet or the moon, there is almost no gravity to hold the spacecraft on the surface.
Several possible methods for collecting samples
Tianwen-2 is planned to try several ways to collect material from the asteroid.
In one method, the spacecraft would hover near the surface and collect loose grains and dust. Such collection could be accomplished by suction or a mechanism that propels material from the surface into the sample chamber.
Another method would involve the spacecraft briefly touching the asteroid's surface and attempting to collect larger rock particles. A similar method was used in missions Return of samples Previous ones, in which contact with the asteroid lasted only a few seconds.
The spacecraft may also try to attach arms or anchoring mechanisms to the surface. A more stable contact could allow it to collect material from a deeper layer and not just dust that has been exposed to the space environment for millions of years.
Each method involves risks. The surface may be soft, rocky, dusty, or uneven. It is also possible that Kamuolewa is not a single solid rock, but a pile of fragments held together by weak gravity.
What will the labs be able to discover?
Laboratory analysis is much more precise than telescopic observation. Researchers will be able to examine the composition of minerals, the microscopic structure of grains, and the isotope ratios of various elements.
Isotope ratios serve as a kind of fingerprint of the material. If Kamua'alwa formed from the moon, the characteristics of the samples would be expected to match those of lunar rocks collected by the Apollo, Luna, and Chang'e missions.
The tests will also be able to determine how long the material was exposed to the solar wind and cosmic radiation, what the intensity of space weathering was, and what changes it has undergone since it separated from its parent body.
If the samples turn out to be similar to LL-type chondrites, this would strengthen the possibility that this is an asteroid that came from a familiar family of rocky objects.
Even a result that rules out a lunar origin would be important. In science, the rejection of a popular hypothesis can be just as significant as its confirmation.
Lessons from the Yabusa-2 and OSIRIS-REx missions
Previous missions have shown the importance of returning asteroid samples to Earth.
The Japanese spacecraft Hayabusa2 returned samples from the asteroid Ryugu. Analysis of these samples revealed carbon-rich material, minerals altered by the presence of water, and organic molecules.
The American OSIRIS-REx mission returned samples from the asteroid Bennu. They also found minerals and components that could not be fully identified through observations from Earth.
In both cases, it turned out that the asteroid's appearance and spectrum did not tell the whole story. The laboratories were able to reveal details about the objects' composition, history, and the environment in which they formed.
Tianwen-2 is supposed to apply a similar approach to an object of controversial origin.
Kamuawalwa illustrates how difficult it is to identify the origin of small objects using remote observations alone. Some measurements support the possibility that it formed from the moon, while other analyses suggest it is a normal asteroid whose surface has been altered by millions of years of exposure to space.
The samples Tianwen-2 will collect could decide the outcome. If it is found to be from the moon, it would be material that was naturally ejected from the moon and entered an accessible orbit around the sun. If it turns out to be a main-belt asteroid, it would provide information about the ways in which small objects migrate into Earth’s vicinity and how space weathering alters their appearance.
Either way, the mission could expand knowledge about the history of the Earth-Moon system, the movement of Near-Earth asteroids And about the conditions that prevailed in the inner solar system at the beginning of its development.
Questions and Answers
What is Kamoʻoalewa? A small asteroid that orbits the Sun in an orbit similar to Earth's and appears from our perspective as if it is accompanying Earth.
Is Kamu'aluwa another moon of Earth? No. It is not gravitationally bound to the Earth and does not orbit it. It is defined as a semi-satellite.
What does the name Kamuaalwa mean? This is a Hawaiian name describing a celestial object that moves or sways from side to side.
What is the size of the asteroid? Its diameter is estimated at about 30 to 60 meters.
How fast is it spinning? It completes a rotation around its axis approximately once every 28 minutes.
Why do researchers think it might be a fragment from the moon? The light reflected from its surface bore a certain resemblance to the spectrum of lunar material that had undergone space weathering.
What is the alternative option? It may be a rocky LL chondrite asteroid, whose surface has been altered by prolonged exposure to the space environment.
What is space weathering? A change in the surface of rocks due to solar wind, radiation, and impact of tiny particles.
What is Tianwen-2? A Chinese spacecraft sent to explore Kamua'aluwa, collect samples from it, and return them to Earth.
Why is collecting samples difficult? The asteroid is small, rotates rapidly, and its gravity is very weak.
How will the spacecraft collect material? It may hover above the surface and collect dust, briefly touch the asteroid's surface, or use attachment mechanisms to reach deeper material.
How will they know if the material came from the moon? The researchers will compare the minerals and isotope ratios in the samples to those of known lunar rocks and asteroid samples.
Why isn't it enough to use telescopes? Telescopes mainly measure the surface layer, whose composition and appearance can vary greatly due to space weathering.
When will final answers be received? Only after the samples are collected, returned to Earth, and analyzed in laboratories has a final conclusion been made about the origin of Kamua'alwa.
More on the subject on the science website
- Proposal: Test samples from Mars in a quarantine facility on the Moon before bringing them to Earth
- Baseball-sized rover successfully operates autonomously on the moon
- Organic material was found on an asteroid sample returned by Yabusa 2
- Did Jupiter help keep the ingredients for life near Earth?
- A small asteroid passed close to Earth
