Tardigrades survived ten days in open space
Tardigrades are tiny animals with eight stubby legs, usually about half a millimetre long when fully grown. They are nicknamed water bears and moss piglets. In 1773 Johann August Ephraim Goeze called them, in German, little water bears, and the name stuck.
Their best-known trick is drying out. When their surroundings lose water, they pull in their legs and shrink into a dry, curled-up form called a tun. In this state their metabolism stops, and they can last for years without food or water. Given water again, they revive.
As tuns, they have survived temperatures from close to absolute zero to well above the boiling point of water, at least for short periods. That raised an obvious question: could they survive space itself?
A ride on the outside
In September 2007, the Foton-M3 mission carried European Space Agency experiments into low Earth orbit. One of them, called TARDIS, for Tardigrades in Space, held dried tardigrades of two species, Richtersius coronifer and Milnesium tardigradum, in exposure hardware on the outside of the capsule.
During the twelve-day flight, the samples were exposed to space for ten days. Some faced only the vacuum. Others faced vacuum plus part of the Sun's ultraviolet light, and others vacuum plus its full range, the ultraviolet our atmosphere normally filters out.
Vacuum alone did them no significant harm. The ultraviolet was the real danger. Among those exposed to the limited ultraviolet range, 68% of the Milnesium tardigradum revived, but only one Richtersius coronifer did. Under the Sun's full ultraviolet, only three animals survived, all Milnesium tardigradum.
The results, published in 2008 in Current Biology, made tardigrades the first animals reported to survive direct exposure to space. The project's leader, Ingemar Jönsson of Kristianstad University, said that the vacuum, with its extreme drying and cosmic radiation, was not a problem for them.
It helps to be clear about what they did not do. They didn't live or move about in space; they were dormant the whole time, and surviving meant waking up afterwards on Earth. The question the experiment left open is how their cells protect their membranes and DNA while dry, and it is still being studied.
In the 2007 experiment, what harmed the tardigrades most?
Dried tardigrades survived ten days in the vacuum of space in 2007; it was the Sun's unfiltered ultraviolet, not the vacuum, that killed most of them.
