China Extends Its Reach into Solar System with Launch of Asteroid Mission

Liftoff aboard a Long March 3B rocket at 1:31 pm EDT (17:31 UTC) from the Xichang launch base kicked off the second mission in a series of Chinese probes to explore the Solar System. This mission, designated Tianwen-2, follows the Tianwen-1 mission, which became the first Chinese spacecraft to land on Mars in 2021.

Chinese officials confirmed the 2.1-metric ton Tianwen-2 spacecraft unfurled its fan-shaped solar arrays shortly after launch, marking an auspicious start to a decadelong tour of the Solar System.

China has two objectives for Tianwen-2. First, Tianwen-2 will fly to a near-Earth asteroid designated 469219 Kamoʻoalewa, or 2016 HO3. Once there, the spacecraft will retrieve a rocky sample from the asteroid's surface and bring the material back to Earth in late 2027 for analysis in labs. After the spacecraft releases its sample carrier to land on Earth, Tianwen-2 will change course and head to a mysterious comet-like object found between the orbits of Mars and Jupiter.

Tianwen-2 will become the first Chinese spacecraft to bring home celestial material from beyond the Moon, where China has landed two previous sample retrieval missions. China's exploits at the Moon have made its space program the world leader in 21st-century lunar exploration, at least for now.

But the Chinese space program lags behind the United States in exploring the Solar System. NASA and Japan's space agency have returned samples from asteroids before, while the European Space Agency has orbited a comet. Tianwen-2 will attempt to do both on a single mission.

Scientists believe the asteroid selected for Tianwen-2 is less than 60 meters (200 feet) in diameter and could be made of material thrown off the Moon sometime in its ancient past. Results from Tianwen-2 may confirm that hypothesis.

Asteroid Kamoʻoalewa is a unique target for a sample return mission. The asteroid is a "quasi-satellite" of the Earth, meaning its orbit around the Sun closely matches that of our own planet. This keeps Kamoʻoalewa relatively close to Earth throughout the year, making it an attractive candidate for a sample return mission.

That's one reason why Tianwen-2's roundtrip journey to asteroid Kamoʻoalewa will last just two-and-a-half years. Japan's Hayabusa 2 asteroid sample return mission lasted six years from launch through its return to Earth, while NASA's OSIRIS-REx mission made the trip to an asteroid and back in seven years. Both visited near-Earth asteroids more distant than Kamoʻoalewa, where Tianwen-2 will arrive in July 2026 and start searching for a location to retrieve samples.

Tianwen-2 will try to collect samples in several ways. One method will involve maneuvering the spacecraft close to the surface and matching the asteroid's rotation and then extending a robotic arm to gather specimens. The spacecraft will also descend to the asteroid's surface for a "touch-and-go" similar to the way Japan's Hayabusa 2 spacecraft and NASA's OSIRIS-REx sampled their asteroids.

Scientists also hope to try another sampling method known as "anchor-and-attach," where the spacecraft will secure itself to the asteroid's surface using four arms with drills at the ends of them. Chinese officials have not said how much material they hope to bring back to Earth, but Tianwen-2 is reportedly designed to collect at least 100 grams of rocks and dust from the asteroid.

Mission planners know little about the shape of Kamoʻoalewa, but long-range measurements suggest it spins once every 28 minutes, relatively fast for an asteroid. This spin rate, coupled with the object's tenuous gravity, will complicate Tianwen-2's maneuvers near the asteroid.

Once it has the samples in hand, Tianwen-2 will depart the asteroid in early 2027 and head for Earth, where it will release a reentry module containing bits of Kamoʻoalewa for landing in late 2027. Researchers will study the specimens to determine their basic physical properties, chemical, mineral, and isotopic compositions, textures, and structures, according to a paper published in the research journal Earth and Planetary Physics.

In the paper, four Chinese scientists write that results from the sample return will not only improve knowledge of asteroids, but could tell us about the Earth and the Moon.

"Confirming the origin of Kamo’oalewa, from its prevailing provenance as debris of the Moon, could be a promising start to inferring the evolutionary history of the Moon," the scientists write in the journal. "This history would probably include a more comprehensive view of the lunar far side and the origin of the asymmetry between the two sides of the Moon."