China's asteroid mission aims to uncover Solar System's oldest secrets

Tianwen-2 will bring back asteroid samples and study a mysterious object that behaves like a comet

China's Tianwen-2 probe, on a Long March-3B carrier rocket, lifts off from Xichang Satellite Launch Centre, in the south-western province of Sichuan. EPA / Xinhua

China’s latest deep space mission aims to investigate whether rocky debris ejected from planetary surfaces in the early Solar System could have helped distribute life’s key ingredients across space.

The Tianwen-2 spacecraft, launched on May 29, is on its way to collect material from a small near-Earth asteroid that may be a piece of the Moon. After that, it will travel even farther to study a mysterious object in the asteroid belt that behaves like a comet.

Researchers hope the samples will offer fresh clues about how planets like Earth were formed, and whether rocks could have travelled between worlds, carrying water, organic molecules or even microbes with them.

“We selected two targets for this mission: the asteroid 2016 HO3 and the main-belt comet 311P,” said Chen Chunliang from the China Aerospace Science and Technology Corporation.

“Both targets hold significant scientific value. The mission allows us to develop new asteroid exploration technologies while collecting data that could help us better understand how the Solar System began.”

The asteroid, also known as Kamoʻoalewa, is a strange little object just 40 metres wide. It orbits the Sun in sync with Earth, making it a “quasi-moon”, an asteroid that stays close to our planet but does not orbit it directly.

An artist impression of Kamo'oalewa near the Earth-Moon system. Photo: Addy Graham/University of Arizona

Its exact origin is uncertain, but one leading theory suggests it may be a chunk of the Moon that was blasted into space by an ancient impact.

Prof Erik Asphaug, a planetary scientist at the University of Arizona, said the asteroid is a perfect example of the mix of space rocks that circle near Earth, including pieces of the Moon, dead comets, broken-up asteroids and leftovers from the early Solar System.

“By studying samples from what may be a fragment of the Moon, scientists can figure out how intense the impact was that launched it into space, and whether those conditions could have been survivable for tiny life forms on a planet like Mars,” he said.

That idea ties into a scientific theory known as panspermia, the possibility that life, or the ingredients for it, may have travelled between planets inside rocks ejected by powerful impacts.

Scientists are also interested in the asteroid’s size and spin rate. It completes one rotation every 28 minutes, which is too fast for loosely held-together pile of rocks to stay intact.

Mr Asphaug said this could suggest that the asteroid is a single solid piece of rock, or a monolith.

“But how do you eject a 40 metre intact chunk of rock from the Moon, when to escape it has to be accelerated to lunar escape velocity, which is about 2 kilometres a second? This is five times faster than a high-powered rifle bullet,” he said.

“That is the geophysical adventure of Tianwen-2. The compositional adventure may be less stunning, if indeed it is a fragment of the lunar crust, but there’s a great deal to learn from its process of ejection,” said Mr Asphaug.

“And I guess there’s a small chance that we’ll be completely surprised, that it’s not a fragment of the Moon at all, in which case there is a lot of explaining to do.”

An unfurled solar panel on Tianwen-2, after its launch on May 29. CNSA/Xinhua

Tianwen-2 will attempt to return samples from the asteroid to Earth by 2027. After completing that phase, the spacecraft will use an Earth gravity assist to journey to comet 311P/PANSTARRS, an object in the asteroid belt that occasionally shoots comet-like tails.

The second part of the mission will take several more years, with the spacecraft studying the comet’s surface and behaviour in detail.

“In space exploration it has become obvious that there is a most-bang-for-the-buck way of going about asteroid and comet exploration,” said Mr Asphaug.

“Consider Nasa’s OSIRIS-REx asteroid rendezvous mission … having returned its sample, now it is heading to a second rendezvous, this time with asteroid Apophis.

“But this secondary mission was not part of the original mission so is subject to ongoing budgetary pressure.”

Japan also has a similar mission, with the Hayabusa2 having successfully returning samples of the Ryugu asteroid in 2020, and is now heading towards another small asteroid.

China’s mission builds on the country’s growing portfolio of successful robotic space flights.

In 2020, Chang’e-5 returned samples from the Moon’s near side. Two years later, Chang’e-6 brought back the first samples from the Moon’s far side − another global first.

The Tianwen-2 mission also comes at a time when Nasa is struggling with major budget cuts, forcing delays and downsizing across several of its flagship science programmes, including plans for Mars sample return.

China is developing its own Mars sample return programme, potentially launching later this decade.