Tardigrades Came Back Alive From Open Space

On the European Space Agency's FOTON-M3 satellite in September 2007, a small experiment called TARDIS bolted samples of two tardigrade species to the outside of the spacecraft. The animals were freeze-dried into a glassy survival state called a tun, then exposed for ten days to the vacuum of low Earth orbit. Some samples saw only the cold and the lack of pressure. Others were left uncovered, soaking up the unfiltered ultraviolet light that comes off the sun above the atmosphere.

The vacuum-only samples mostly came back. Rehydrated in lab water, they crawled and laid viable eggs. The UV-exposed samples did much worse, but a few in each species still revived and reproduced. It was the first animal known to survive direct exposure to space.

The trick is the tun. When a tardigrade dries out, it pulls in its legs, halts its metabolism almost completely, and replaces most of the water in its cells with sugars and intrinsically disordered proteins that lock the cellular machinery in place like resin. Thomas Boothby's group at the University of Wyoming identified the key proteins, called TDPs, in 2017. Yeast and even human cells engineered to produce them gain a noticeable measure of desiccation tolerance.

A tun can also shrug off temperatures from near absolute zero to over 150°C, ionizing radiation thousands of times the human lethal dose, and pressures six times deeper than the ocean. Yet a healthy active tardigrade, swimming in a drop of moss water, dies in any of those conditions within minutes. The toughness is not a property of the animal. It is a property of the dehydrated pause it can put itself into.