The movie Passengers was far from the most scientifically sound space adventure movie of the last few years. But for all its weaknesses and mediocrity, the plot—where interstellar space travelers “hibernate” to conserve energy as they travel to colonize a distant planet—was on to something.
“It stands to reason if you lower metabolic rate of the body, you lower energy usage,” said Hannah Carey, a researcher at the School of Veterinary Medicine at the University of Wisconsin-Madison, whose lab has extensively investigated hibernation in mammals on Earth. “When we want to think about how humans might exist in the final frontier, hibernation may be a key part of that journey.”
In science fiction movies like Passengers, hibernation is portrayed in the form of suspended animation, or putting a body on ice and preserving it indefinitely. This might be useful in the future, but it’s impractical for traveling within the solar system (say, to Mars), where transit times will most likely be a few months to start off with.
But something milder, like hibernation, would still be a boon to helping us conserve energy and resources on something like the six-month trip to Mars. Hibernation is mainly characterized by a physiological state called torpor, where our metabolic activity and body temperature is reduced to conserve energy. If we could figure out how to hibernate like mammals, we could theoretically conserve our resources over the long commute to Mars and beyond.
“It’s still a somewhat polarizing idea within NASA,” said John Bradford, an aerospace engineer and the president and COO of SpaceWorks Enterprises, a company looking at new technologies essential to commercial space travel—including artificial induction of torpor in astronauts.
“But it’s a great research area, and we think this technology will really be enabling for finally getting us out of low earth orbit—something we’ve been talking about for way too long. I think people are ready for us to stop talking and finally get out there."
Hibernation might also solve a few other space-related obstacles. Astronauts in microgravity consistently suffer from muscle atrophy and bone density loss. Currently, our only way to limit those effects is through rigorous exercise. But hibernating mammals avoid physiological decline, even after months of inactivity, thanks to reduced cell function. Torpor in astronauts could serve the same protection—as well as give us an excuse to dump that heavy equipment off the spacecraft.
And hibernation might keep people a little more sane as well. “If you imagine traveling to Mars, or even a one year lunar mission, and you stay with your crew for that long, always in strict contact and close quarters, it’s easy to run into issues related to psychological and mental health,” said Matteo Cerri, a physiology researcher at the University of Bologna and a consultant for the European Space Agency who’s researched inducing hibernation in non-hibernating organisms like humans. You can’t get cabin fever if you’re sleeping the months away.
Synthetic torpor could also solve problems related to the damage cosmic radiation can inflict on the human body, an unresolved obstacle to deep space travel. Since hibernating astronauts can all reside in a single room, you can build a smaller spacecraft that’s easier and cheaper to fortify against radiation.
So how do you induce synthetic torpor in the human body?
Depends on who you ask. Bradford and his think the key is in therapeutic hypothermia, where hypothermia is induced to help limit tissue and organ damage in patients experiencing poor blood flow.
“For us, the question was, ‘What can we do now?’” said Bradford. “We want to be able to support really the first missions to Mars, in the 2030s timeframe.”
Therapeutic hypothermia is already an established medical practice, and while it’s induced for no more than two to three days, some studies show its possible to safely put the human body into a controlled hypothermic state for as long as 14 days.
According to Bradford, safely reducing body temperature by just 5 to 10 degrees can slow down the body’s metabolism (i.e. energy consumption) by 50 to 70 percent. That could effectively halve the amount of food and other resources needed to sustain an individual in space every day.
Here’s how SpaceWorks thinks hibernation in space could work. There might be an upper deck of the habitat capsule that’s cooled down to set astronaut core body temperatures between 89 and 93 degrees Fahrenheit. The sedated crew would be resting in beds with instruments measuring vitals and feeding tube. They’d be “hibernating” in 10 to 14 day cycles, punctuated by two of three days of wakefulness in between. At least one or two crew members would be awake at any moment to handle anything urgent.
It sounds like a good plan, but one huge problem stands in the way: Hypothermia is a hazardous condition for humans. “There are real limitations, especially in any prolonged use of hypothermia, to tissue function and viability,” Carey said. The unnatural drop in heart rate and breathing could rapidly cause cardiac arrest, interrupting blood flow that in turn starves organs tissues of oxygen.
That’s why Carey endorses a more natural approach to torpor that reverses how hypothermia works by lowering body temperature itself. This way, the body won’t try to fight against temperature changes through automatic responses like shivering.
“It’s thought that this is more likely to be a safer way to lower temperature and achieve those beneficial effects of hypothermia, without having to go against the natural physiology of humans,” said Carey.
Other groups are looking into whether metabolism can be attenuated directly at the cellular level, identifying key chemical components and genes involved in the hibernation process. Maybe there’s a particular drug or hormone that’s applied, or maybe astronauts undergo some sort of gene therapy that allows decreases their metabolic activity and body temperatures.
Regardless, once that cause is determined, the real question for space researchers is whether those innate mechanisms can be induced safely in modern humans—all while maintaining clear airways, controlled breathing, preventing cardiac problems and organ failure, and infections that might arise from a worsened immune system. This won’t be like the movies where someone just wakes up from stasis and is ready to be human after five minutes; becoming active after weeks in torpor will take a day or two.
For Bradford and Cerri, this could all be achieved within a generation’s time—if funding and resources are allotted, and testing in humans is made possible. “Ultimately, we need to send hundreds of thousands of people to Mars if we’re really going to colonize it,” said Bradford. “Our current approach won’t really cut it.”