How China Could Win the Race to Return Rocks from Mars

Scientific American

4 days ago

On May 14, 2021, China's Tianwen-1 lander plummeted from space to streak through the skies above Mars's vast plain of Utopia Planitia, with an aeroshell protecting it from the heat and plasma of its high-speed atmospheric entry. After unfurling its parachutes and pulsing its engines to zero in on an amenable landing site, the spacecraft touched down safely onto the Red Planet, where it deployed a rover, Zhurong, to explore the surrounding alien landscape. This engineering feat was hugely significant, confirming China as a major player in planetary exploration. With Tianwen-1's touchdown, China became the only other nation ever to successfully land on Mars besides the U.S. Moreover, the mission also paved the way for a far more ambitious and unprecedented project.
That project, Tianwen-3, is set to launch via two Long March 5 rockets from Wenchang spaceport on the Chinese island of Hainan in late 2028. One launch will carry Tianwen-3's lander, while the other will transport the mission's Mars orbiter, which is also an Earth-return vehicle. The mission aims to collect samples of Martian rock and soil for delivery back to Earth, where subsequent studies could, potentially, redefine our understanding of life itself and our place in the cosmos.
'Tianwen-3 will be the first mission aiming to bring back material from another planet to search for signs of life,' says Li Yiliang, a professor of astrobiology at the University of Hong Kong and one of the authors of a paper published in Nature Astronomy on June 19 that offers new details on the mission. (Tianwen-2, another Chinese sample return mission, launched in May 2025 but is bound for a near-Earth asteroid as well as a comet; China has also pulled off two successful lunar sample return missions, Chang'e 5 and Chang'e 6.)
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Tianwen-3 will use the same approach as Tianwen-1 to make planetfall in a yet-to-be-selected landing area. The vagaries of spacecraft engineering, however, demand the site should be somewhere in the midlatitudes of the planet's northern hemisphere; it also must be at an altitude of at least three kilometers below the planet's average elevation so that more of Mars's thin air can serve to slow Tianwen-3's descent. The lander will use proven tech from China's lunar explorations, drilling as deep as two meters for subsurface samples and scooping up material from the surface. Additionally, a helicopter drone—following the lead of NASA's pioneering Ingenuity flights —will collect selected additional rock and loose particle samples from within around 100 meters of Tianwen-3's landing site.
The lander will operate for around two months on the surface, in which it will use scientific payloads such as a ground penetrating radar and a Raman spectrometer to gather more data on the broader geological context for collected samples. When the time comes, it will fire off a solid rocket booster to send a canister containing at least 500 grams of material into Mars orbit to dock with the waiting orbiter-returner spacecraft. The eventual return trip should bring Tianwen-3's samples home sometime in 2031.
Once on Earth, the samples will be swiftly secured and transported to a custom-built Mars sample laboratory, where they'll be extensively analyzed while carefully following 'planetary protection' policies meant to prevent any potential otherworldly cross-contamination.
Although Tianwen-3's objectives range from investigating Mars's interior to studying its wispy atmosphere, scientists working on the mission are most eager for what it might reveal about the planet's possible former or even extant life. If, in fact, anything ever dwelled on the Red Planet, then Tianwen-3's samples could conceivably contain various telltale signs of its presence—so-called biosignatures.
A convincing biosignature could come in different types, Li says. For example, Tianwen-3's scientists will be seeking molecules directly produced by Martian organisms to fulfill known biochemical functions, akin to the DNA and RNA molecules that life-forms on Earth rely on to store and transmit genetic information. Another biosignature is biogenic isotope fractionation—the distinctive way that living organisms alter the natural ratios of stable isotopes in their ecosystems; on Earth, for instance, biochemical processes such as photosynthesis prefer the lighter carbon-12 rather than heavier carbon isotopes, leading to detectable shifts in the proportions of these isotopes with respect to the surrounding environment. A third approach, Li adds, would be to look for fossil evidence, such as the imprints that microbes may leave behind in mudstones and other fine-grained sedimentary rocks.
China's astrobiological focus for its Martian explorations is 'a laudable, ambitious goal,' says Mahesh Anand, a professor of planetary science and exploration at the Open University in England. 'This is exactly what we have been recommending over the years: to look for any signs of biogenic activity or even just to understand that there was a habitable environment. The rest of the global planetary science community would love to get answers to these questions.'
China's approach is simpler in many ways than the U.S.-led Mars Sample Return (MSR) mission, which is a joint project between NASA and the European Space Agency (ESA). MSR's workhorse, NASA's Perseverance rover, is already on Mars, where it has spent more than four years collecting dozens of carefully selected samples from Jezero Crater, a diverse site harboring an ancient river delta and other complex geological features that may preserve evidence of past life. In contrast, Tianwen-3's sampling will be limited to its immediate surroundings, which will probably be more drab—because although a boring, flat landscape may be of less astrobiological appeal, it is far easier to land on. And the spacecraft's landing ellipse—the area within which Tianwen-3 is most likely to touch down—spans some 50 by 20 kilometers, meaning a precision touchdown to visit any especially alluring targets is highly unlikely.
But, largely because of its greater complexity and cost, MSR is under threat of cancellation from the Trump administration following years of delays and cost overruns. The project's potential elimination, however, would be only one of many grievous blows to NASA's science, the funding for which the Trump administration has proposed to cut by nearly half.
'The reason why NASA went with Perseverance as this first step was so that you would have this curated, intentionally selected and well-recorded process and contextual process of where these rocks came from,' says Casey Dreier, chief of space policy at the Planetary Society, a U.S. space science advocacy group. 'This isn't intended in any way to denigrate the achievements of the Chinese robotic program, but in general I think you can characterize a lot of [its] framing as symbol-driven and capability-focused over the direct science return.'
China's more basic engineering-led plan, with the science trailing after, may put limits on the questions Tianwen-3 can realistically answer. But this methodical, step-by-step approach to progressively building and demonstrating critical capabilities is exactly what has now positioned China to take the lead in the race to return rocks from Mars. Meanwhile, the far more elaborate MSR has floundered.
Dreier says that this moment, in which the U.S. appears to be ceding leadership in this area to China, will have implications for global space exploration.
'The U.S. needs to lead and work with its allies to continue to invest in these big, bold efforts to make potentially historic discoveries,' Dreier says. If the White House has its way, he adds, then Perseverance's samples might only find their way back to Earth after an even more complex, expensive and distant human spaceflight program led by SpaceX lands astronauts on Mars. Which means, for now, China will get its shot at a major first in space exploration.
'The way I look at it is that China is starting to explore Mars,' Anand says. The richer science on offer from a complex MSR-style plan is enticing, he says, but sticking to simplicity and clearly achievable near-term results 'probably has a higher chance of returning science than planning on something that might take decades.'
U.S. and European scientists have for generations seen obtaining samples as a 'holy grail' for Mars exploration. For China, retrieving Martian material fits into the strategic framework of its broader, solar system-encompassing Tianwen program, the name of which translates to 'heavenly questions.' Beyond Tianwen-3 and its already-launched asteroid-and-comet-bound sibling Tianwen-2, there is also Tianwen-4, slated for liftoff around 2029, which will target the Jupiter system and its intriguing Galilean moon Callisto. Future missions in the Tianwen series, including to the ice giants Uranus and Neptune, are also under consideration.
For Li, Tianwen-3 remains the Tianwen program's most compelling project, in part because its path to Mars and back is so straightforward; although lofty, its objectives still appear eminently within reach. 'It is important for humanity to understand its position in the solar system and the universe,' he says, because this would mark a profound milestone in human history. And, on the threshold of attempting to bring back the first samples from Mars—with the possibility of finding the first-ever evidence for alien life within them—China is now uniquely poised to achieve this milestone.