Outer space, explained.
Reaching Mars without fail, collecting surface samples and bringing them home will be an extraordinary engineering feat (Alan Dyer/VWPics/Universal Images Group via Getty Images)
Returning Martian material safely is only half the job; showing the world it was done safely is the other half.
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China is bringing Mars to Earth – and then the checking beginsChina is bringing Mars to Earth – and then the checking begins
China plans to bring Martian rocks and soil back to Earth. Getting them here will be only half the challenge.
Last week, China announced plans for a dedicated planetary-protection laboratory (Opens in new window) in Hefei (Opens in new window), in eastern China. The facility will receive samples returned by the Tianwen-3 mission, open and process their containers, and assess whether any of the material poses a biological risk.
Tianwen-3 is expected to launch in 2028 and return by 2031 (Opens in new window), carrying material (Opens in new window) that could reveal Mars’s geological history and whether life once existed there. Reaching Mars without fail, collecting surface samples and bringing them home will be an extraordinary engineering feat. But landing the return capsule will not be the end of the mission. Nobody will simply open the lid.
Planetary protection runs in both directions. Earthly microbes hitching a ride could contaminate Mars or the returned samples. A discovery hailed as Martian life might inadvertently turn out to be an inadequately sterilised terrestrial stowaway. The danger in the other direction is much less likely but potentially more consequential. Scientists cannot simply assume that untreated Martian material is harmless before examining it. Sensible safety systems must allow for what we do not yet know.
Anything exposed to Mars must remain securely contained until it is found safe or sterilised.
Mars sample return therefore falls into the strictest category of an internationally developed system known as planetary protection. Under the framework established by the Committee on Space Research (COSPAR) (Opens in new window), Tianwen-3 is a Category V “restricted Earth return” (Opens in new window) mission. In plain English, anything exposed to Mars must remain securely contained until it is found safe or sterilised.
China has done more than simply promise to follow this framework. A national planetary-protection standard (Opens in new window) came into effect in February 2025, and an English-language edition was approved (Opens in new window) that July. Chinese experts sit on COSPAR’s planetary-protection panel alongside specialists from the United States, Europe, Russia, Japan, India and elsewhere.
In January, China presented Tianwen-3’s developing safeguards at a COSPAR meeting in Athens attended by representatives from 11 space agencies. The mission will also carry five cooperative scientific payloads (Opens in new window) led by teams in Italy, Hong Kong and Macau, as well as by COSPAR’s Panel on Exploration.
The emerging plans show what those commitments mean in practice. Hardware that will touch the samples receives the strictest treatment. Components are repeatedly checked for microbes, cleaned or sterilised, then checked again. Protective covers stay in place until the equipment is needed on Mars. Once collected, the material must be sealed behind several barriers, with any Martian dust on the container’s exterior sterilised before the journey home.
The laboratory itself must do two seemingly contradictory things. Biological-containment facilities are designed to keep potentially hazardous material in. Pristine-sample laboratories are designed to keep earthly contamination out. Hefei must achieve both at once: a stray terrestrial microbe could compromise years of analysis, while material from inside must not be released untested.
The Atlantis basin on Mars (ESA/DLR/FU Berlin)
Chinese researchers have proposed four key decision points (Opens in new window) at which the mission should not proceed without evidence that its protections are working: before leaving Earth, before leaving Mars, before re-entering the Earth’s atmosphere and before any sample is released from quarantine.
They have even assembled a microbial “most-wanted list” from Chinese spacecraft and clean rooms. From thousands of organisms collected during spacecraft assembly, researchers selected 359 strains (Opens in new window), representing more than 80 species, against which cleaning, detection and sterilisation methods can be tested. Nearly 70% form spores, which can survive harsh conditions and be difficult to eradicate.
This work deserves more attention than it has received. It strongly suggests that China is not treating planetary protection as a box-ticking exercise or an unwanted foreign demand. Standards, specialist facilities and years of advance preparation point instead to serious, good-faith engagement with a shared scientific responsibility.
That does not remove every question. We do not yet know who will conduct Tianwen-3’s four reviews, how independent they will be, whether the findings will be made public or whether international experts will take part. COSPAR can advise when invited, but it does not serve as a global inspector. Ultimately, each country certifies its own compliance.
The constructive response is not to presume that China will cut corners. It is to encourage China’s space authorities to make the validation process visible enough to earn confidence abroad. International participation would reinforce the substantial work already under way.
Making room for such participation would not diminish China’s ownership of the mission. Planetary protection is a shared problem: confidence in both the science and the safety measures cannot stop at national borders. Space cooperation has often survived political tensions on Earth. American and Russian specialists still operate the International Space Station together (Opens in new window), because keeping people safe in orbit depends on technical trust and daily cooperation. Planetary protection offers another area where common interests can outweigh strategic rivalry.
If Tianwen-3 succeeds, as I hope it does, China may be the first country to return samples directly from Mars. That will make the mission a landmark not only in exploration but in scientific stewardship. Bringing Mars to Earth will be astonishing. Showing the world that it has been done safely may prove just as important.
About the author
Richard de Grijs
Richard de Grijs (Opens in new window) is Professor of Physics and Astronomy at Macquarie University and former Executive Director of the International Space Science Institute–Beijing.
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