Nothing says interstellar travel like a hibernation pod. The heroes of the 2016 holiday blockbuster Passengers, played by Jennifer Lawrence and Chris Pratt, embark on a century-long journey to an planet outside our solar system. Hibernation pods extend their lifespans for the long trip, but they wake from torpor 90 years earlier than scheduled. Then they set about trying to fix the ship and trying to put themselves back to sleep.
First of all, let’s talk about this ‘waking’ from hibernation business. Hibernation may involve lying down with ones eyes closed, but there’s no sleeping going on; In fact, a long stretch of it leaves the body sleep deprived. If this movie were true to life, the first thing that would happen when Jennifer Lawrence opened her long-lashed eyes in the hibernation pod would not be her listening to the ship computer’s crew update. It would be her closing those long lashes again and descending straight into sleep.
That’s because sleep is one of the bodily functions that can’t be done properly in hibernation. During the periodic arousal states that punctuate hibernation, animals warm their bodies and go straight into a long, deep sleep. Oxford neuroscientist Vlad Vyazovskiy did his master’s work at the Institute of Cryobiology at Kharkov University in Ukraine, where he studied ground squirrels in torpor.
“Originally hibernation was considered a continuation of sleep, but physiologically it is very different because your metabolism is totally suspended, although it is still regulated,” says Vyazovskiy. “Torpor, this extreme metabolic challenge, seems to do something to the brain or body which necessitates sleep, which in turn provides some type of restoration.”
Suspended animation in deep space flight has been a movie trope since the dawn of science fiction, and for just as long Nasa has been working to make it real. John Bradford of SpaceWorks Enterprises has been contracted by Nasa to develop just such a technology. Inspired by the unique physiologies of animal hibernators, he is working on overriding the body’s steady 37•C core temperature in a technique called Targeted Temperature Management. Metabolism slows by about seven percent for every degree of cooling. Though uncontrolled hypothermia can be fatal, a constant 32• body temperature still allows for normal nerve functions that are critical for breathing and heart beats.
“Humans can’t hibernate, but we can mimic how animals hibernate,” he says. “Earlier in our evolutionary history we did hibernate, but now it’s turned off.”
Did I mention he’s an engineer? Am I the only one who gets worried when engineers are hired to do doctorish things? For one thing, in true hibernators, platelets and white blood cells are sequestered in lymph nodes away from the blood vessels during dormancy. This prevents the blood clots that can form with inactivity and avoids the inflammation that causes kidney damage upon rewarming. There will be a lot of research necessary before humans can safely hit the pause button on their metabolisms. Luckily, Bradford hasn’t been permitted any real live human subjects yet.
Then again, doctors have been pursuing this capability for years in the field of emergency medicine. When a severely injured patient arrives at a hospital, minutes count. A rapid cooling of the body saves tissues that are cut off from blood supply—a slower metabolism consumes less oxygen—so cooling patients for surgery is now a routine procedure. A low dose of narcotics prevents the patient from shivering to warm themselves up. In China, experiments with therapeutic hypothermia put patients into a deep chill for up to two weeks before successfully reviving them.
It really would be great if we could make it happen. The advantages of crew hibernation could mean the difference between a successful Mars colonization and an Earth-bound humanity. Mars is only six months’ journey from Earth, so life extension is not the primary issue at play, but hibernation pods would cut down the required habitat size and food needs. They could even provide solutions to some of spaceflight’s most longstanding health issues. Spinal fluid rising into the skull in low gravity causes pressure that diminishes most astronauts’ eyesight in flight, but the hibernation state should help to clear up that issue.
When humans live without the strain of gravity, muscle atrophy and bone loss also become a problem. Those on the International Space Station have to put in two full hours of exercise per day just to maintain their skeletons. But with hibernation, muscles and bone can be maintained using neuromuscular stimulation, which is unpleasant while conscious but not an issue for a deep-sleeping crew member.
“We can exercise you all day long!” says Bradford.
Cancer risk from the accumulated exposure to cosmic rays is Nasa’s primary health concern for astronauts on long-haul space flights, and there is some debate as to whether a slowed metabolism is more vulnerable—unable to fend off damage to DNA by repairing it—or more immune, because errors in that repair process often trigger the tumours.
In either case, hibernation may be the answer, because it restricts the astronaut’s range of motion. Magnetic shielding could protect a spacecraft’s inhabitants from ionizing radiation, but the shield for a whole habitat would be far too heavy to be feasible. If shields could be produced for a small cot, however, and the astronaut’s prone body could be protected for the voyage within it, the shield option could be back on the table.
In the future, human hibernation could take even more radical paths. A research group supported by the US Army is experimenting with a technique that cools patients rapidly by replacing their blood with ice-cold saline solution. The total metabolic suspension leaves a body with no heartbeat, no breathing and no discernible brain activity, but when dogs have undergone the treatment, they have been successfully resuscitated after three hours in the frozen state.
Perhaps those dogs will want to be the first interstellar passengers, to take them far away from a planet where their lot in life is to have their blood replaced by ice.