In September 2007, the European Space Agency launched roughly 3,000 tardigrades into low Earth orbit aboard the Biopan-6 platform on the FOTON-M3 mission. Known as water bears, these microscopic animals were dried into a dormant state before being exposed directly to the vacuum of space, alongside doses of solar and cosmic radiation, for ten days at an altitude of around 258 to 281 kilometres. It marked the first time any animal had been tested under fully open space conditions, without shielding of any kind. According to the study published in Cell Press Journal, titled ‘Tardigrades survive exposure to space in low Earth orbit’, most tardigrades survived vacuum exposure alone without difficulty. Among those additionally exposed to UV-A and UV-B radiation, 68% of Milnesium tardigradum specimens revived within 30 minutes of rehydration back on Earth, although many later died. The findings placed tardigrades alongside lichens and bacteria as organisms capable of enduring the harshest conditions space has to offer.
How did ESA test tardigrades in low Earth orbit
One set was exposed only to space vacuum, a second to vacuum together with UV-A and UV-B radiation, and a third to vacuum combined with the full solar UV spectrum, from vacuum-UV through to UV-A. All groups were additionally exposed to ionising solar and galactic cosmic radiation throughout the flight, while desiccated control samples remained on the ground under normal laboratory conditions.This design allowed researchers to isolate the effects of vacuum alone from the added burden of ultraviolet exposure. As the paper explains, only anhydrobiotic organisms capable of surviving near-total desiccation stood any real chance in these conditions, and few could be expected to withstand unfiltered solar radiation on top of that. Tardigrades were selected precisely because of their known tolerance for extreme drying and high radiation doses.
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How did tardigrades survive space vacuum and UV radiation
Both species survived exposure to space vacuum alone extremely well, showing no meaningful difference from the ground-based control samples. Once solar radiation was added, however, survival decreased, particularly among animals exposed to the full UV range, where only three specimens of M. tardigradum survived.The figure most often cited comes from the group exposed to vacuum plus UV-A and UV-B only. The study reports that “a high proportion (68%) of the M. tardigradum specimens revived within 30 minutes” of rehydration, although many of these died shortly afterwards. R. coronifer fared far worse under the same conditions, with only a single specimen reviving. Eggs exposed to vacuum alone hatched at rates comparable to controls, but none exposed directly to solar light produced juveniles.
How did tardigrades become the first animals to survive open space
The findings marked a significant first for animal biology. As per the European Space Agency, project biologist René Demets described the discovery as something new, saying “nobody knew about that capability” before this experiment. Until then, only lichens and certain bacterial spores had been shown to survive the combined assault of space vacuum and unfiltered solar and cosmic radiation.The results raised further questions about how tardigrade cells stabilise their DNA and membranes during extreme dehydration, and whether similar mechanisms might one day inform research into radiation damage and repair in other organisms. The TARDIS mission has since been followed by further experiments, including studies on the International Space Station; the 2007 flight remains the reference point for demonstrating that an animal can survive direct exposure to the space environment.
