No spacesuit, no capsule, no protective shielding of any kind: for about ten days in 2007, thousands of microscopic animals floated in low Earth orbit fully exposed to the vacuum of space. Most of them survived. The experiment, carried out by the European Space Agency, remains one of the most striking demonstrations of biological toughness ever recorded, and it turned a barely-visible invertebrate called the tardigrade into a minor celebrity of astrobiology.
Astrobiology experiments typically test how well simple organisms, bacteria and other single-celled microbes, hold up under conditions found beyond Earth’s atmosphere, since complex multicellular animals are generally assumed to be far more fragile. The 2007 tardigrade flight mattered precisely because it broke that assumption, putting an actual animal with organs, a nervous system, and a reproductive cycle through a test previously reserved for the hardiest microbes. That result reshaped how researchers think about the outer limits of what animal life, not just single cells, can survive.
The FOTON-M3 mission and its tiny passengers
The experiment flew aboard ESA’s FOTON-M3 mission in September 2007, using an external platform called BIOPAN-6 that opened to expose samples directly to the space environment once the spacecraft reached orbit. Researchers loaded roughly 3,000 dehydrated tardigrades, drawn from two species, Richtersius coronifer and Milnesium tardigradum, onto the platform before launch. For about ten days, orbiting between 258 and 281 kilometers above Earth, those samples sat completely unprotected, exposed to the cold, airless vacuum of space and to solar ultraviolet radiation far more intense than anything reaching the surface of Earth, details confirmed in the European Space Agency’s own summary of the experiment.
Why dehydration is the trick that makes survival possible
Tardigrades cannot survive vacuum exposure in their normal, hydrated state any more than most animals could. The key to the experiment was a survival strategy tardigrades evolved long before humans existed: when conditions turn hostile, dry, frozen, or otherwise lethal, they can expel nearly all the water from their bodies and curl into a dried, barrel-shaped state called a tun. In that state, metabolic activity drops to a level so low it is difficult to measure, and the animal’s cellular machinery is protected by a combination of specialized proteins and sugars that keep vital structures from collapsing as water is lost. It was tardigrades in this dormant tun state, not active, hydrated ones, that were loaded onto the BIOPAN-6 platform before launch.
What happened when the samples came back to Earth
After the spacecraft returned, scientists rehydrated the samples and monitored which tardigrades revived. Results varied by exposure condition: animals exposed to vacuum alone, without added solar radiation, showed survival rates comparable to control groups that never left Earth, while those additionally exposed to the full range of solar ultraviolet radiation showed sharply reduced survival, though a meaningful fraction still revived within roughly 30 minutes of rehydration. Crucially, some of the tardigrades that survived went on to reproduce normally after returning to Earth, producing viable offspring and demonstrating that the exposure had not caused lasting reproductive damage, results published in the peer-reviewed journal Current Biology under the title “Tardigrades survive exposure to space in low Earth orbit”.
How tardigrades compare to every other organism tested this way
The 2007 flight marked the first time any animal had been shown to survive direct, simultaneous exposure to the vacuum of space and space radiation without any protective enclosure, a distinction that separated tardigrades from bacteria and other extremophile microorganisms that had previously demonstrated some tolerance for individual stressors like radiation or desiccation in isolation. Tardigrades are known among biologists for tolerating an unusually broad combination of extremes, including near-absolute-zero temperatures, pressures many times greater than at the bottom of the ocean, and extended dehydration lasting years, but the space vacuum experiment tested several of those stressors simultaneously and in a context no laboratory freezer or pressure chamber could replicate. Background on the full range of extreme conditions tardigrades have been shown to tolerate is compiled in the Wikipedia entry on the tardigrade.
A dormant hitchhiker that already reached the Moon
Long before the 2007 orbital flight, tardigrades had already spent more than two centuries building a reputation for turning up in extreme places. German zoologist Johann August Ephraim Goeze first described the animals in 1773, and the name tardigrada, meaning slow stepper, was coined shortly afterward by the Italian biologist Lazzaro Spallanzani. More than a thousand species have since been identified living in nearly every environment on Earth, from moss and lichen in ordinary backyards to Himalayan peaks, deep ocean trenches, and the ice of Antarctica, wherever a thin film of water lets them feed and reproduce between bouts of dormancy. That same tun-state dormancy resurfaced in an unplanned experiment in April 2019, when Israel’s Beresheet spacecraft, carrying a digital archive from the nonprofit Arch Mission Foundation that included a small number of dehydrated tardigrades, crashed while attempting to become the first privately funded lander to reach the lunar surface. Whether any of those tardigrades survived the impact has never been confirmed, but the incident pushed space agencies and mission planners to reconsider planetary protection rules for privately funded missions carrying biological material toward other worlds.
Why the experiment still shapes astrobiology research
The FOTON-M3 results reshaped how scientists think about the theoretical possibility of life surviving transfer between planets on debris ejected by asteroid impacts, a concept known as panspermia, since tardigrades demonstrated that at least one complex, multicellular animal could endure the kind of raw space exposure such a journey would involve, even if only for a period measured in days rather than the years or centuries such a trip would actually require. The experiment has also become a standard reference point in discussions of what kinds of Earth life might plausibly survive on the surface of Mars or other planetary bodies, informing planetary protection protocols designed to prevent accidental contamination of other worlds by hardy Earth organisms hitching a ride on spacecraft. Nearly two decades later, the BIOPAN-6 tardigrade flight remains the clearest experimental evidence available that complex animal life, not just single-celled microbes, can withstand the vacuum of space itself.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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