China has a space station and, in just a few short years, has landed robots on the moon and Mars. This week the country’s space agency is targeting new, far-flung destinations and setting off for an asteroid that could contain secrets that explain how Earth and the moon formed.
The country’s Tianwen-2 spacecraft is lifted off aboard a Long March 3B rocket from the Xichang Satellite Launch Center in southwest China on Thursday around 1:31 a.m. local time, according to state media. (it was still Wednesday in New York).
After about a year, the robotic mission will arrive at 469219 Kamoʻoalewa, a near-Earth asteroid. There, it will perilously try to scoop up some rocky matter, and then swing back around to Earth. A capsule filled with geologic treasure would then plunge toward the planet for retrieval by scientists in late 2027.
If Tianwen-2 pulls this off, China will become the third nation — after Japan and the United States — to retrieve pristine material from an asteroid.
“All Chinese planetary scientists are now finger-crossed for this historic mission,” said Yuqi Qian, a lunar geologist at the University of Hong Kong.
The spacecraft also has a secondary target, an unusual comet that it could study as part of an extended mission.
Visiting these objects will help reveal more about the building blocks of the worlds of the inner solar system. And as asteroids can pose an impact risk to Earth, missions to study the structures and mineral makeups of these objects can aid planning to deflect or vaporize them.
“A sample return mission is a gift that keeps on giving,” said Sara Russell, a planetary scientist at London’s Natural History Museum.
While fragments of asteroids reach Earth’s surface periodically, they are contaminated and altered when they plummet through the atmosphere. Scientists prefer untouched matter from the source, brought back to study in ultraclean laboratories.
“Sample return missions allow us to pick apart the physical and chemical properties of a body in a level of detail that’s not possible with remote observations by telescopes and spacecraft,” said Ashley King, a meteoriticist also at the London museum.
Japan has accomplished this twice, with its Hayabusa spacecraft raiding the asteroids Itokawa in 2005 and Ryugu in 2019. NASA’s sample return mission to the asteroid Bennu, Osiris-Rex, pulled off the same feat in 2020.
China’s space agency has executed two successful sample return missions to the moon — in 2020 and 2024. But Tianwen-2 (Tianwen is often translated as “Questions to Heaven”) is China’s first foray into asteroid sample return.
Kamoʻoalewa, the asteroid it will visit, is somewhat peculiar. As a quasi-satellite earlier known as 2016 HO3, it loops around Earth, but it is not a true moon, because it is gravitationally bound to the sun. Recent telescopic observations, though, suggest it is made of the same volcanic matter found on the moon, implying that it is a piece of the lunar surface shorn off by a meteor impact.
“Kamoʻoalewa, therefore, potentially holds key information about the formation and evolution of the Earth-moon system,” Dr. King said.
However “its origins remain an open question,” said Benjamin Sharkey, a planetary astronomer at the University of Maryland who made those recent telescopic observations. He said he was excited that Tianwen-2 was going to bring some of the asteroid home for study, which should close the case of Kamoʻoalewa’s origins.
China has revealed few details about how Tianwen-2 will work. An academic paper posted last year offers some clues. A variety of cameras and infrared imagers will ascertain Kamoʻoalewa’s shape, size, spin and mineral makeup, while a radar system will map its internal structure.
By looking at the thermal properties of Kamoʻoalewa, Tianwen-2 will also help study the Yarkovsky effect. When sunlight hits a rotating asteroid, its sunward side heats up. As it continues to spin, it cools down, which nudges the asteroid, like a small thruster. Over time, escaping heat can push a harmless asteroid onto an Earth-impacting orbit.
Kamoʻoalewa can get within nine million miles of Earth, making it an easy target to reach. But diving down to sample it is risky. “The sample collection and return are hardest,” Dr. Russell said, “because humans have only a very limited amount of experience in doing both.”
The asteroid may be only 130 feet across — a small target. Its rapid rotation, about once every 28 minutes, poses additional challenges. “You need to find ways to either grab the sample without landing or a way to hang on as it spins,” Dr. King said.
China’s spacecraft may try doing both. “Tianwen-2 will use two methods to collect samples from Kamoʻoalewa,” Dr. Qian said.
The first is “Touch and Go,” a method employed by the U.S. and Japanese asteroid missions: The spacecraft briefly makes contact with the object, kicks up the surface (using compressed gas, or a fired projectile) and captures jettisoned rocks before the spacecraft flees the scene.
The second method, “Anchor and Attach,” has never been tested. Using a series of drills, Tianwen-2 will try to adhere to the asteroid before retrieving both shallow and deeper samples.
If Tianwen-2 navigates those dangers and eventually drops its bits of Kamoʻoalewa to Earth, it will then fly to the Comet 311P/PanSTARRS, arriving in the early 2030s to study it remotely.
While most comets witnessed from Earth travel on long-haul journeys around the sun, 311P is a main belt comet. These icy curiosities stay within the asteroid belt between Mars and Jupiter.
“These types of objects remain very mysterious,” Dr. Sharkey said, not least because icy rocks should not exist this close to the sun’s warm glow. But they may help explain how Earth became a planet with vast oceans.
Tianwen-2 is more than just a scientific sleuth. It is also a technological steppingstone for China’s ambitious Tianwen-3 mission. Due to launch in 2028, it aims to retrieve rock samples from Mars and return them to Earth. A comparable effort led by the United States to achieve the same goal is facing major hurdles.
But the race for the red planet should not overshadow China’s first bid to acquire shards of an asteroid.
“This is very exciting,” said Richard Binzel, a planetary scientist at the Massachusetts Institute of Technology. “But asteroids present their own challenges.”
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