Why China’s upcoming Tianwen-2 mission could be significant for finding clues about quasi-satellites

If successful, the mission will place China in a group of a handful of countries — including the United States and Japan — which have been able to sample asteroids and return the samples to Earth successfully.

Kamo‘oalewa was discovered in 2016 by the Pan-STARRS 1 asteroid survey telescope on Haleakalā in Hawaii. (Ilustration/NASA)

Written by: Alind Chauhan

4 min readNew DelhiMay 25, 2025 12:02 PM IST First published on: May 25, 2025 at 08:15 AM IST

China will launch its first mission to survey and sample a near-Earth asteroid this week. Known as the Tianwen-2 mission, the probe will investigate an asteroid called 469219 Kamo‘oalewa, which orbits the Sun at a distance relatively close to Earth.

If successful, the mission will place China in a group of a handful of countries — including the United States and Japan — which have been able to sample asteroids and return the samples to Earth successfully.

“This is an ambitious mission to explore a fascinating object,” astrophysicist Amy Mainzer of the University of California, Los Angeles, told the journal Science. Here is a look at the mission, the Kamo‘oalewa asteroid, and why China wants to investigate it.

What is the Kamo‘oalewa asteroid?

Kamo‘oalewa was discovered in 2016 by the Pan-STARRS 1 asteroid survey telescope on Haleakalā in Hawaii. It is one of just seven asteroids that fall into a little-understood class known as quasi-satellites of Earth — satellites that orbit the Sun, but because of their close distance to Earth, they are gravitationally influenced by the planet.

The asteroid “travels in a highly elliptical solar orbit and appears to Earth-bound observers to be alternately leading and trailing Earth in its more circular orbit. This gives the impression the asteroid orbits Earth,” according to a report in Science.

Quasi-satellites are known to shift their orbits over time. For instance, Kamo‘oalewa has been in its current orbit for around 100 years, and is expected to remain there for the next 300 years.

Why does China want to investigate Kamo‘oalewa?

Kamo‘oalewa has garnered attention due to its unusual orbit and unknown origin. Scientists believe exploring this asteroid would help them find clues about how quasi-satellites came to be, and how their orbits evolved over time.

Moreover, some researchers suggest that Kamo‘oalewa could be the first known asteroid composed of lunar material.

In 2021, University of Arizona planetary scientist Benjamin Sharkey and colleagues wrote in the journal Communications Earth & Environment that Kamo‘oalewa might have been ejected from the Moon’s surface due to a collision with some other astronomical object. They said so because the telescope that they used to investigate Kamo‘oalewa picked up a usual spectrum, or pattern of reflected light, that suggested Kamo‘oalewa is composed of silicates resembling those found in Apollo lunar samples.

The exploration of the asteroid could settle the hypothesis that the Moon was formed as a result of a collision between the Earth and another small planet (Kamo‘oalewa could be a small remnant of that collision).

“Observations and the ejecta models do not yet prove it…[the samples in an Earth-based lab could] settle the question [of origin] definitively,” Mainzer said.

Also in Explained | A short history of China’s rise as a space power

How will Tianwen-2 retrieve samples?

To collect the samples from Kamo‘oalewa, the Tianwen-2 mission will use a “touch-and-go” technique which has been successfully implemented by the United States’ OSIRIS-Rex and Japan’s Hayabusa2 missions.

In this technique, the spacecraft hovers close to the surface of the asteroid while a robotic arm fires an object or burst of gas to knock fragments into a collection chamber.

Depending on the surface conditions, the Tianwen-2 probe might also use a second “anchor and attach” technique. In this, four robotic arms extend and drill into the surface to retrieve material.

After collecting the samples, the mission will drop them on Earth. The probe will then head towards the main asteroid belt for another mission.

Experts, however, suggest that collecting samples from Kamo‘oalewa will be a challenging task for Tainwen-2. The issue is that, unlike previously explored asteroids, Kamo‘oalewa is quite small. It measures just 40 to 100 metres in diameter. As a result, the mission would need highly sophisticated cameras, spacecraft computers, and reaction control systems.