After 400 days of travel, the Chinese Tianwen-2 probe has reached your goal: object 469219 Kamo’oalewa (2016HO3). The entire world astronomical community has its sights set on this trip, for the answers it can provide to a mystery that has been going on for more than a decade. However, as usually happens with missions carried out by China, we had little information about the journey until the ship was already at its destination. This occurred on July 4, although the Chinese National Space Administration, CNSA, announced it this July 6.
Be that as it may, the important thing is that China has reached Kamo’oalewa, that terrestrial “minimoon” that has given scientists so many headaches since it was discovered in 2016.
Now comes the good. Tianwen-2 was released on May 29, 2025. 400 days later, it has reached its first stop, just 20 kilometers from Kamo’oalewa. There, he has taken the first photos, which will help him map this object, in order to determine the best places for sampling. Then, it will be time to get down to work, to collect a series of samples that will be sent to Earth in 2027. Then, we will have a definitive answer to the million-dollar question: Is Kamo’oalewa an asteroid or a fragment that was ejected from the Moon?
The instruments. This probe has 11 payloads, including instruments that will allow it to study both Kamo’oalewa and its next target: comet 311P/PANSTARRS. These instruments include cameras, laser measuring devices, spectrometers, sonar radars and particle analyzers. It also includes the DIANA dust analyzer, developed in Italy.
First mission: map the surface. Currently, the Chinese probe is taking photographs from different angles to create a 3D model that will allow establishing the best places to take samples. Broadly speaking, these places must meet two requirements: be scientifically interesting and not pose risks for sampling. The latter includes, for example, no unstable ground or loose rocks.
Second mission: take samples. Since the mission left without knowing exactly what the surface of Kamo’oalewa will be like, Tianwen-2 travels prepared to take samples through three different methods: suspension, touch and match and anchor and coupling.
The first consists of keeping the probe in hover, without landing on the object, and taking out a robotic arm that will skim the surface to obtain the samples. The second method, on the other hand, uses a disc-shaped, gas-powered head that briefly but more strongly touches the surface. Afterwards, rotating brushes are released that, together with bursts of air, sweep away the material released with that blow of the disc. Finally, the anchoring and docking method consists of releasing four robotic arms that are fixed to the surface to extract material for a longer period of time. It would be the first time this method has been used in deep space.
Tianwen-2 has been traveling for 400 days
Third mission: send them to Earth. The samples will be sent to Earth in 2027 for analysis. However, during Tianwen-2’s flyby of Kamo’oalewa, some inquiries are already being made about it.
Asteroid or lunar fragment? Until now, all that was known about Kamo’oalewa were hypotheses or estimates. It was believed to measure between 40 and 100 meters in diameter and that It had to be a fragment released from the Moon after a collision or an asteroid. The first hypothesis arose from a study using spectrometry, in which it was concluded that its surface is rich in silicates, like that of the Moon. The second has several origins, although gained weight after another study in which several collisions were modeled on a simulated Moon. In very few cases the released fragments became quasi-satellites of the Earth, so the asteroid would fit better.
In its first days in the vicinity of Kamo’oalewa, Tianwen-2 has made a measurement of the surface reflectance of the object, which suggests that it has a high geometric albedo. That of the Moon is quite low, so the asteroid hypothesis would still fit. On the other hand, the first data indicate that Kamo’oalewa measures 20 meters in diameter. It is less than what was originally estimated, but practically the same as what was calculated with observations made by James Webb. According to a study published on July 1in these it was calculated that it would measure 18 meters and, again, it was suggested that it be an asteroid. Specifically, one of type E.
What is this about quasi-satellites? Kamo’oalewa is considered a quasi-satellite of the Earth because, when viewed from our planet, it appears to revolve around us. But it’s not true. In reality, this object revolves around the Sun, like the Earth. What happens is that it has a period similar to that on Earth. It also takes about a year to completely circle the sun. This, together with the geometry of its orbit, creates that optical effect that it is actually a kind of terrestrial mini-moon.
Now we know that, possibly, in addition to not being a mini moon Due to its orbit, it is not made of fragments of our satellite either. At least, it seems most likely, although, of course, we will have to wait for the samples to reach Earth. Then we can definitively put the mystery to rest.
Image | CNSA
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