A Chinese spacecraft built to collect specimens from an unexplored asteroid and return them to Earth successfully launched Wednesday from a military-run spaceport in the country's mountainous interior.
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 decade-long tour of the Solar System.
China's objectives for Tianwen-2 are two-fold. 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.
Two in one
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, or 200 feet, in diameter, and could be made of material thrown off the Moon some time 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 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 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."
Tianwen-2's mothership, with 11 scientific instruments, will commence the second phase of its mission after dropping off the asteroid specimens at Earth. The probe's next journey will bring it near an enigma in the asteroid belt named 311P/PanSTARRS in the mid-2030s. This object is one in a rare class of objects known as active asteroids or main-belt comets, small worlds that have tails and comas like comets but loiter in orbits most commonly associated with asteroids. Tianwen-2 will be the first mission to see such an object up close.
Stepping into the Solar System
Until the last few years, China's space program has primarily centered on the Moon as a destination for scientific exploration. The Moon remains the main target for China's ambitions in space, with the goal of accomplishing a human lunar landing by 2030. But the country is looking farther afield, too.
With the Tianwen-1 mission in 2021, China became the second country to achieve a soft landing on Mars. After Tianwen-2, China will again go to Mars with the Tianwen-3 sample return mission slated for launch in 2028.
Tianwen, which means "questions to heaven," is the name given to China's program of robotic Solar System exploration. Tianwen-3 has a chance to become the first mission to return pristine samples from Mars to Earth. At the same time, NASA's plans for a Mars Sample Return mission are faltering.
China is looking at launching Tianwen-4 around 2029 to travel to Jupiter and enter orbit around Callisto, one of its four largest moons. In the 2030s, China's roadmap includes a mission to return atmospheric samples from Venus to Earth, a Mars research station, and a probe to Neptune.
Meanwhile, NASA has sent spacecraft to study ever planet in the Solar System, and currently has spacecraft at or on the way to the Moon, Mars, Jupiter, a metal asteroid, and in interstellar space. Another US science mission, Dragonfly, is scheduled for launch in 2028 on a daring expedition to Saturn's moon Titan.
But NASA's science division is bracing for severe budget cuts proposed by President Donald Trump. In planetary science, the White House's budget blueprint calls for canceling a joint US-European Mars Sample Return mission and several other projects, including the DAVINCI mission to Venus.