In space, no one can hear you sleep — but it’s possible that alarms could one day wake astronauts on alien worlds hundreds or thousands of light years away. This is the promise and potential of suspended animation, sometimes called human hibernation or “cryosleep.” While it’s still (mostly) the stuff of science fiction, new advancements in snooze-related science could turn this into a tired-and-true method for space exploration.

So settle in, grab a pillow, and let’s get started.

Getting Up to Speed

The best thing about the universe? It’s huge. There’s always something new to discover, from cotton candy planets to six-star solar systems and supermassive black holes.

The worst thing? It’s massive. Consider the star nearest to us, Proxima Centauri. While it’s just around the corner in galactic terms — a mere 4.25 light years away — do the math and you’ll discover it’s more than 40 trillion kilometers from Earth. According to NASA, the Voyager 1 spacecraft, now traveling at 17.3 km/s, would take more than 73,000 years to reach the Proxima Centauri system. At the speed of light, the journey would still take almost four and a half years.

For astronauts, this is daunting. A review in the Gravitational and Space Biology Bulletin notes that, even with faster propulsion systems, there are a host of problematic physical and psychosocial effects associated with long-term space exploration that could negatively impact mission outcomes. But what if there was another way?

Suspended animation could be an alternative to traditional travel. Controlled reduction of humans’ overall body temperature could effectively send space travelers into a state of hibernation, allowing for significantly reduced consumption of resources while simultaneously avoiding some of the negative effects of long-term cohabitation in cramped crew quarters.

The Science of Sleep

Both NASA and the European Space Agency (ESA) have begun preliminary research into cryosleep solutions. But how exactly would this suspended snooze-fest work?

It all starts with torpor, a hypermetabolic state already seen in animals such as hummingbirds that significantly reduces their body temperature and, in turn, the amount of energy required to keep their bodies alive. While torpor bears similarities to true hibernation, including lowered body temperatures and slowed processes, torpor cycles typically require daily food foraging. Meanwhile, hibernation relies on increased resource consumption prior to deep sleep but is associated with much longer periods of reduced activity. Successful snooze-based solutions for astronauts are about splitting the difference.

“If we were able to reduce an astronaut’s basic metabolic rate by 75% — similar to what we can observe in nature with large hibernating animals such as certain bears — we could end up with substantial mass and cost savings, making long-duration exploration missions more feasible,” notes Dr. Jennifer Ngo-Anh, a research team leader for the ESA study. If humans could be put into a state of controlled torpor that reduced consumption needs without requiring the massive pre-feed to sustain hibernation, it could be our ticket to the stars.

The good news? This idea isn’t just science fiction. Controlled hibernation has been used to help improve recovery after serious events, such as gunshot wounds, and reduce the risk of brain damage during surgery. In practice, this requires the slow decrease of internal body temperature.

“Slow” is the operative word here. If cooling happens quickly, the human body registers the change as hypothermia and fights hard to get back to a baseline temperature states. Shivering is one of the most common methods to help achieve this equilibrium but causes skin and nerve damage — not exactly ideal for explorers. Controlled cooling that uses tools such as ice packs, IV solutions and water pads can to help encourage a more sustainable state of suspended animation.

Cold Comfort

The not-so-good news? Best efforts have managed to keep bodies cold for just three days before baseline instincts take over. This isn’t enough for intrepid explorers; to make long-term space travel possible, astronauts would require low-temperature torpor that lasts for months or years without damaging their bodies.

This raises another critical point: getting old. While the term “suspended animation” sounds like a moment frozen in time, it can’t avoid the aging process. This means that a suspended animation adventure to Proxima Centauri is probably out of the question at current speeds — while the 73,000 year-old crew would still be cold on arrival, it would have nothing to do with technology or torpor. They’d simply be long dead of old age.

There is a theoretical workaround here, but it’s not ideal. It’s called vitrification, and it requires the removal of all bodily fluids, which are replaced by antifreeze. Bodies are then frozen solid and thawed out upon arrival, with the antifreeze drained and replaced by blood and other necessary liquids. This would effectively stop the process of aging — and since antifreeze doesn’t crystallize like common bodily fluids, astronauts could be reanimated without damage.

The downside? Death is required to start the process, and if something goes wrong during the wake-up cycle, the ship effectively becomes a cryo-coffin. So far, vitrification remains an operational outlier. While it’s often touted as a way to live forever by pseudo-scientific cryostasis companies, they only have half the process down. They can kill you and fill your body with antifreeze, but the technology required for effective unfreezing doesn’t exist, meaning you could be waiting a while (or forever) for your wake-up call.

Spaced Out

The biggest “waste” of space on exploratory craft? Crew quarters. From beds to toilets to food storage and enrichment activities, more astronaut accommodations mean more weight for the spacecraft and more time spent getting the ship up to speed.

According to New Atlas, new research around magnetic thrust drives offers some promise of a faster future, but the type of rocket technologies slated for use in upcoming missions depend on small, sustained thrust over time that eventually gets explorers where they’re going. By putting crew members into a state of hibernation and reducing the footprint needed for quarters, it’s possible to solve two exploratory problems with one cold stone. Lower weight means faster travel, and the crew (hopefully) won’t be stir-crazy by the time they arrive.

This prospective change in capacity planning also has several knock-on effects for crew safety, specifically when it comes to interstellar radiation. One of the biggest challenges with galaxy-wide travel? No sun. Once astronauts are out beyond the heliosphere and into the true darkness of space, they lose any protective benefits conferred by our sun and are fully exposed to high-energy radiation. While material shielding on spacecraft can help to reduce the radioactive effects, long-term exposure is cumulative — which means the more time it takes for explorers to reach their destination, the greater the chance they’ll be permanently harmed.

However, with collective cryosleep, the radiation risk could be more effectively managed. As an article in Life Sciences in Space Research suggests, hibernation states offer greater protection against damaging radiation. Also, by putting the crew in more tightly packed “pods” instead of typical crew quarters, it’s possible to surround astronauts with naturally protective barriers — such as water containers, per the ESA — that could help to limit overall radiation exposure.

Wake Me Up (Before You Go-Go)

Crews in cryosleep also face the critical challenge of waking up. If ships reach the red planet, Proxima Centauri or other systems deeper into the galaxy but the crew can’t get of bed, we’ve got a problem.

Even with better torpor-including technology, it may not be possible (or advisable) to keep crews in suspended animation for the entire trip. Instead, it’s more likely that astronauts will need to be woken on regular schedules to ensure they’re still healthy and address any issues that emerge on the spacecraft itself. If there’s one thing that space faring films have taught humans as a species, it’s that something inevitably goes wrong with the ship when humans are in cryosleep. Maybe it’s an asteroid. Maybe it’s a sudden systems failure. Or maybe it’s a sneaky alien invasion. No matter the issue, no one wants to get stuck drifting millions of kilometers off course after a century or so in hibernation.

Trial Run

While we probably won’t be jetting off to the Centauri systems anytime soon, ongoing advancements in suspended animation and spacecraft propulsion could possibly lead to a torpor trial run to a local destination, such as Mars or Jupiter’s moon Europa. With trips measured in high months or low years rather than decades or centuries, handling potential problems becomes challenging rather than impossible.

As space agencies around the world gear up for the next phase of interstellar exploration, suspended animation might just be the wake-up call we need.