It's one small step for Tardigrada, and one giant leap for the animal kingdom: The toughest creature on Earth has survived a trip into space.

Except for a few hardy strains of bacteria, any other creature would have been destroyed – but tardigrades handled the voyage as though it were a dry spell on their local moss patch.

"They have claws and eyes. They are real animals. And this is the first time such an animal was tested in space," said Petra Rettberg, an Institute of Aerospace Medicine microbiologist.

Better known as water bears, tardigrades are eight-legged invertebrates visible to the naked eye and found throughout the world, making them a biology class favorite.

They're capable of halting their metabolisms during times of extreme privation, and can repair DNA damage caused by extraordinary doses of radiation – a phenomenon that's piqued scientific curiosity and prompted researchers to shoot tardigrades into naked orbit around the Earth.

"The repair – how fast, how efficient, with or without errors – is different, but basic damage is the same," said Rettberg, who helped design a tardigrade containment system attached to the Foton-M3satellite, launched last September by a consortium of national space agencies.

The tardigrades had already been coaxed into an anhydrobiotic state, during which their metabolisms slow by a factor of 10,000. This allows them to survive vacuums, starvation, dessication and temperatures above 300 degrees Fahrenheit and below minus 240 degrees Fahrenheit.

Once in orbit, the tardigrade box popped open. Some were exposed to low-level cosmic radiation, and others to both cosmic and unfiltered solar radiation. All were exposed to the frigid vacuum of space.

Back on Earth, tardigrades that had basked in cosmic radiation revived and reproduced at rates comparable to an unexposed control group. Those dosed with solar radiation were less likely to wake – but that even a few survived, wrote Rettberg's team in findings published today in

Current Biology, was remarkable.

Just how the invertebrate astronauts protected themselves "remains a mystery," wrote the researchers. Rettberg's next task is to identify the responsible genes – a basic step, perhaps, in better understanding and improving human DNA repair.

Tardigrades may even provide insights into adaptations necessary for survival in off-Earth colonies, though they could not live actively in the extreme and nutrient-poor environments of Mars or the moon.

However, Rettberg cautioned against expecting too much from such early findings.

"It'll just be interesting to see what the mechanisms are in tardigrades, compared to the very simple ones in bacteria and more complex systems in higher organisms," she said. "But in addition, it's just fun."

Tardigrades survive exposure to space in low Earth orbit [Current Biology]

*Images: Noemi Guil Lopez; Goldstein Lab. *

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