Did you know Earth has a ‘minimoon’? It’s known as asteroid 2016HO3, or Kamoʻoalewa.
A probe sent for the China National Space Administration (CNSA) mission, Tianwen-2, has just returned its first picture of the quasi-satellite, named after a Hawaiian chant for an oscillating object in the sky.
The probe is CNSA’s first asteroid sample-return mission, which launched on 29 May 2025 from the Xichang Satellite Launch Center.
Now, after 13 months of travel across around 1 billion kilometers (around six hundred million miles) of space, Tianwen-2 has arrived at its primary destination, the agency says.
Since July 2, the probe has been hanging out about 20 kilometers from Kamoʻoalewa, from which it snapped this portrait of the ‘minimoon’.
Kamoʻoalewa is too distant to be considered a bona fide Earth satellite, and its main orbit is around the Sun. But since it skirts our planet in an elliptical orbit every 45 years, it qualifies for rare ‘quasi-satellite’ status – just one of seven known to orbit Earth.
It’s a member of the asteroid class known as the Apollo asteroids, which more or less share Earth’s orbit around the Sun. However, as a quasi-satellite, Kamoʻoalewa remains near Earth across long periods and multiple orbits.
What we already know about Kamoʻoalewa is scant, based on observations from a distance. It’s approximately 40 to 100 meters in diameter, which means it may turn out to be the smallest asteroid ever visited by human spacecraft.
After its long journey from Earth, Tianwen-2 made its first optical detection of Kamoʻoalewa on June 6, and by June 19, it had approached to within 2,000 km.
By July 2, it was just 20 km away from the asteroid: close enough to capture the image above.
As part of its mission, Tianwen-2 will conduct in-orbit observations of the rock, and collect samples to bring back to Earth, as described in a paper published in Space Science Reviews back in January.
“Among the known near-Earth asteroids, 2016HO3 is an exceptionally rare Earth co-orbital object,” physicist Rongqiao Zhang, of the Lunar Exploration and Space Engineering Center in Beijing, and his colleagues, explained in a research article in January.
“As an Earth quasi-satellite, its orbital period is close to that of Earth, enabling low energy transfer, and it maintains a stable distance of about 0.1–0.3 AU from Earth, providing favorable conditions for tracking, control, and communication.”
Scientists want to know if it’s a pile of rubble or a monolithic body; whether there are traces of water, and what else it’s made of; how its orbit evolved; and whether solar wind has anything to do with it.
The researchers noted that its unusual orbit, enigmatic origin, and unresolved questions about its physical properties “make it a compelling candidate for addressing fundamental questions about the origins of Earth’s quasi-satellites and the dynamical evolution of their orbits”.
The samples it sends back to Earth will help confirm whether Kamoʻoalewa is indeed a bit of Moon, as scientists have deduced from telescope observations.
After this roughly nine-month stop at Kamoʻoalewa, Tianwen-2 will continue on to main-belt comet 311P, which is past Mars. But not before dropping off its capsule of samples from the quasi-moon during an Earth flyby.
311P stands out for its bizarre, six-pronged dust tail, and we’re still not really sure of its shape, so researchers are keen to investigate these questions up close.
The comet also happens to coincide with the trajectory of Tianwen-2’s return mission, so it’s a convenient target for a main-belt flyby.
It’s a big mission for tiny objects, and we can’t wait to see what they discover.
