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 someday 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 diseases such as epilepsy. And trials are underway to see if there is a way to lower the body temperature of people, keep them in a sleeplike 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.