In September 2007, a batch of dehydrated, millimetre-scale animals rode into orbit strapped to the outside of a Russian spacecraft, exposed to nothing but the vacuum of space and the sun’s raw radiation. Ten days later, once the capsule had landed and the samples were rehydrated back in a European laboratory, most of the animals simply woke back up.
The animals were tardigrades — segmented, eight-legged creatures often called water bears, with the largest species barely a millimetre long and most individuals far smaller. The 2007 flight made them the first animals on record confirmed to survive direct, unprotected exposure to the vacuum of space.
Tardigrades are already known for extreme tolerance well beyond spaceflight. They live in temporary ponds and droplets of water in soil and on moist plants, and the same ESA overview of the mission notes that they can withstand temperatures ranging from about minus 272 degrees Celsius to 150 degrees Celsius, survive without water for roughly a decade, and resist radiation doses that would kill most other animals many times over. Around 3,000 of the animals were packed into the Biopan-6 hardware for the Foton-M3 flight specifically to test whether that resilience extended to the vacuum of space itself.
Ten Days Riding Outside a Spacecraft
During ten days in low Earth orbit, at an altitude of 258 to 281 kilometres, samples of desiccated adult eutardigrades from two species, Richtersius coronifer and Milnesium tardigradum, were exposed to space vacuum and two ranges of ultraviolet radiation aboard the European Space Agency’s Biopan-6 platform, flown on the Russian Foton-M3 mission. The animals were dried out before launch and packed into small chambers on the outside of the spacecraft, some fitted with filters to block part of the sun’s radiation and others left fully exposed.
The Swedish and German scientists behind the project, known as TARDIS, wanted to see how the tiny animals would fare once removed from Earth’s atmosphere altogether. “Our principal finding is that the space vacuum, which entails extreme dehydration and cosmic radiation, were not a problem for water bears,” said Ingemar Jönsson, the project’s leader, from the University of Kristianstad in Sweden.
Vacuum Was Survivable, Solar Radiation Was Not
Left alone, the vacuum of space turned out to be the easy part. Researchers reported that both species survived exposure to space vacuum alone very well, with no significant difference in survival pattern compared to samples kept on the ground — the first record of an animal surviving simultaneous exposure to space vacuum and solar or galactic radiation.
Solar ultraviolet light was a different story. Samples shielded behind filters that blocked the shortest, most energetic wavelengths fared reasonably well, but tardigrades exposed to the complete solar spectrum, from vacuum-ultraviolet through UV-A, suffered close to total losses; of the Milnesium tardigradum sent up under those conditions, only three specimens survived. The tardigrades joined a short list of organisms already known to endure harsh conditions on earlier ESA flights, including lettuce seeds and certain lichens, and bacterial spores that can persist for years if shielded from direct sunlight.
A Microscopic Animal That Shuts Down to Survive
Survival at that scale is possible because tardigrades enter a reversible, dried-out state before the stress even arrives. Once dehydrated, the animals fall into such a deep dormancy that they no longer need to eat or breathe, effectively suspending their biology rather than actively resisting the conditions around them until water becomes available again.
What keeps those dried-out cells from collapsing altogether has only recently come into sharper focus. Molecular biologist Thomas Boothby, at the University of Wyoming, and colleagues found that tardigrades rely on a synergy between the sugar trehalose and a family of tardigrade-specific disordered proteins to protect cellular structures as water is lost, rather than on trehalose alone the way many other desiccation-tolerant organisms do. The team reported that the combination, not either ingredient by itself, was required for robust protection during drying.
What Water Bears Suggest About Life Beyond Earth
ESA project biologist René Demets said the tardigrade results reopened a question about where life could have first taken hold. “The question is why are terrestrial organisms prepared to survive exposure to space conditions? Is there a rationale? Nobody knows at the moment,” he said, floating the possibility that life could have originated elsewhere and later been carried to Earth on a meteorite, provided it could also survive the fiery trip through the atmosphere.
ESA has since extended the experiment with a longer-duration project called Expose, mounted on the International Space Station’s Columbus laboratory. “After about one and a half years we will get the Expose trays back and see what the situation is after long duration exposure,” said Martin Zell, then head of ESA’s ISS Utilisation Department, adding that the results could either match the tardigrades’ resilience or reveal a hard limit on how long any organism can endure unprotected exposure to space.
Jönsson himself was careful not to overstate what the flight had shown. Surviving ten days of exposure is not the same as living in space — tardigrades still need liquid water to grow, feed and reproduce, and nowhere in the vacuum outside a spacecraft provides it. What the Biopan-6 flight demonstrated was narrower and still unprecedented: an animal dried out, launched beyond the atmosphere, bathed in raw solar radiation, and brought home capable of waking up again.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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