Bears do it to get through cold winters. So do many smaller mammals, including squirrels and hedgehogs. Even the fat-tailed lemur (a primate cousin of Homo sapiens), living in warm Madagascar, slows down for months when its food supply runs low. But for us humans, hibernation has been an unnecessary and impossible goal. Until now.

Taking lessons from animal hibernators, scientists are using their tricks for medical therapies and may some day adopt them for space travel. Some physicians are employing therapeutic hypothermia – a lowering of the body temperature by a few degrees for several days at a time – to help treat patients with traumatic brain injuries or conditions such as epilepsy. And trials are under way to see if there is a way to lower the body temperature of people, keep them in a sleep-like state for days or weeks and then revive them with no ill effects, something that astronauts may have to do to travel deep into space.

"We see the science has advanced enough to put some of the science fiction into the realm of science reality," says Leopold Summerer, head of the advanced concepts team of the European Space Agency, one of the operators of the International Space Station. "It doesn't mean we will have hibernating astronauts any time soon, but we are learning from nature how to understand some of the things that happen to animals during hibernation, such as preventing bone loss or preventing muscle loss."