Tardigrades Spent Ten Days in Open Space and Lived

Space is not a place an animal can go without a suit. There is no air, no pressure, and nothing at all between you and the Sun's ultraviolet light. In September 2007 a European capsule called Foton-M3 went up carrying about three thousand passengers who had no suits, no cabin, and for ten days no lid over them either: trays of dried tardigrades fixed to the outside of the spacecraft and opened directly to the vacuum.

A tardigrade is less than a millimetre long, has eight legs and walks like a small bear made entirely of upholstery, which is why nearly everyone calls them water bears instead. There are more than a thousand species, living in moss, leaf litter, gutters, deserts, the deep sea and the Antarctic. You almost certainly have some in your garden right now, plodding about in the film of water on a cushion of moss.

When that film of water dries up, a tardigrade does something drastic. It pulls in its legs, collapses into a barrel-shaped ball and shuts almost everything down. The state is called a tun, and an animal in a tun is barely alive in any sense you could measure. It can stay that way for years — the Natural History Museum puts it at up to thirty of them in dry conditions — and then come back with a single drop of water.

That trick was what the experiment was built to test. The dried animals went up as tuns, spent ten days in low Earth orbit with nothing whatsoever around them, came home and were given water. The vacuum by itself did essentially nothing. The animals exposed to it revived at the same rate as the ones that had stayed in a laboratory on the ground. The extreme dehydration and the cosmic radiation, the project's lead researcher said afterwards, were simply not a problem for water bears.

The Sun was a different matter. Tardigrades shielded from sunlight did well. Those given the full solar ultraviolet range mostly did not, and of one of the two species tested, none came back at all. But some did. A number of animals that had taken unfiltered sunlight in open vacuum picked themselves up within half an hour of being rehydrated and walked away, which is something no other animal has ever been shown to do.

We know all this because the experiment was deliberately designed to be unkind in separate ways. The trays sat in a container on the skin of the capsule, and different groups were given different treatments: vacuum alone, vacuum plus part of the ultraviolet range, vacuum plus the whole of it. That is what makes the result readable rather than just impressive, because the damage can be pinned on one thing instead of on space in general. Vacuum, survivable. Direct sunlight, mostly not. The results were published in Current Biology in 2008, under a title as flat as a shipping note.

As for why the tun works at all, the short version is that a dried tardigrade contains almost no liquid water, and most of what vacuum and radiation do to a living thing they do through water. Radiation that would wreck a working cell finds very little in there to wreck. It is the same reason the dried animals shrug off temperatures from around minus 272 degrees Celsius to plus 150, and can go a decade without a drink. It does not make them indestructible. It makes them absent, until the water comes back.