animation about space travel

Suspended Animation In Space Travel: What Scientists Still Need To Learn

Human hibernation could be a great way to get to Mars (and beyond), but a few big questions remain.

By Mary Beth Griggs | Published Oct 16, 2014 8:55 PM EDT

The first astronauts who head off to Mars might make the entire 180-day journey while they’re fast asleep . In a NASA-commissioned study on human stasis , aerospace engineers at SpaceWorks have found that the benefits of placing a crew in suspended animation for the duration of the journey could be legion. Without living spaces or kitchen facilities, the ship carrying the crew could be lighter and smaller. With everyone basically in hibernation, with a lower metabolic rate, future missions can reduce consumables like food and water by up to 70 percent. And having an unconscious crew also reduces the grueling boredom and chances of personality clashes before humanity can complete the small step/giant leap onto the Red Planet.

It sounds practically perfect in every way, but there’s still a considerable amount of time and research that needs to happen before we send astronauts off to Mars via the shores of sleep. The technology that SpaceWorks is looking at is a form of therapeutic hypothermia that will drop the temperature of the astronauts’ bodies by just 5 to 10 degrees Fahrenheit, reducing their metabolism and putting them in a kind of hibernation. “It doesn’t take much to get the body to start slowing down,” says John Bradford, President of SpaceWorks Enterprises.

Though it involves chilly temperatures, therapeutic hypothermia is a hot topic in the medical world, with numerous published studies and trials in the works , all trying to buy trauma patients an increased chance of recovery on the surgeon’s table. Bradford says that SpaceWorks has been paying close attention to the studies coming out of the medical world, and that they think therapeutic hypothermia could be used safely on interplanetary flight, once some of the medical concerns of such an endeavor are studied and addressed.

One of the biggest issues facing human stasis using therapeutic hypothermia involve the simple fact that the method has only been tested in people who have been severely injured. “Nobody has done this on a healthy person,” Bradford says, making it hard to isolate what benefits or problems the method could pose for astronauts in peak condition. Not only that, but the longest medical trials of therapeutic hypothermia have only lasted for 14 days, and a mission to Mars will take at least 180 days for a one-way journey.

Some of the other medical questions that therapeutic hypothermia faces:

• Cognitive function—How will being unconscious for six months affect the human brain, and how long will recovery take? “Is it going to be a couple hours, a couple days?” Bradford says, adding: “We’d like to measure how well you can perform when you get there.” A recovery time on the scale of months would obviously be problematic. Bradford says that initial results from case studies showed that some patients who underwent therapeutic hypothermia actually preformed better cognitively after the procedure than before. Then again, before the procedure, those patients were severely injured, so it’s hard to say how astronauts would react.
• Muscle atrophy and bone loss— Staying in shape is hard enough for astronauts and cosmonauts who are awake. But add being completely sedentary to a weightless environment and the threats of muscle atrophy and bone loss become much more severe. To counter the physiological effects, Bradford says that astronauts in stasis will be treated with drugs to counter the bone loss, and their muscles will be given an electrical workout, stimulated by small electrical impulses. “We can envision that you’re constantly being exercised in this manner,” Bradford says.
• Intracranial pressure—One of the more enigmatic challenges faced by long-term spaceflight projects is the effect of intracranial pressure on astronauts. Researchers have noticed that without gravity, fluids in the body tend to move towards the upper body, raising pressure in the skull, and affecting vision. Bradford says that some medical studies have found that induced hypothermia can reduce cranial pressure in situations here on earth, which gives him hope that it could have a beneficial impact on astronauts.
• Radiation—Exposure to radiation is a huge challenge to long distance spaceflight , but Bradford hopes that stasis using hypothermia could reduce the risk. A summary of the proposed method from SpaceWorks says : “Testing in animals has shown that cancerous tumor growth and the effects of radiation are significantly reduced and slowed during the torpor-state (on par with metabolic rate reduction).” In addition, the savings on mass (no living quarters, less food, etc) mean that a transport vessel using stasis could theoretically be heavily armored against radiation in a way that a larger vessel could not.

Bradford says that the next phases of research will involve longer term testing on animals, then humans, and eventually, humans in space– likely on the ISS. He’s optimistic that with all the ongoing medical tests on therapeutic hypothermia, a viable solution for the Mars mission will be available well before any Mars projects get off the ground. “A space application is just part of it. Instead of developing some niche technology, we’re going to leverage something that’s existing,” Bradford says.

And, just for the record, unlike many science fiction plots where something goes wrong and the capsule containing the astronauts is left to float in space for centuries , if something were to go wrong on a Mars mission using stasis, the hibernation system would automatically shut off, waking the crew and allowing them to make necessary repairs.

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Watch SpaceX launch a Starship to Mars in this gorgeous new animation

SpaceX has big plans for Starship, as the new video shows.

SpaceX's massive new Starship vehicle launches toward Mars in a stunning new video that captures the ambition of Elon Musk's deep-space vision.

The 5-minute animation, which SpaceX posted on YouTube Monday (April 10), begins with a flyover look at Starbase, the company's facility on Texas' Gulf Coast. About a minute in, a Starship lifts off from the seaside site.

The video then shows Super Heavy, Starship 's 33-engine first stage, come back for a landing atop its orbital launch mount. The booster settles in softly, supported by the launch tower's "chopstick" arms .

The 165-foot-tall (50 meters) Starship upper stage, meanwhile, meets up with a tanker in Earth orbit, loading up on fuel for the long trip to Mars .  

Related: SpaceX's Starship looks amazing stacked for launch in these photos

Starship gets there safely, at roughly the same time as three other vehicles, which together create four bright streaks in the dark Martian sky.

The animation ends with a view from inside the just-landed Starship. Its hatch opens, and four spacesuit-clad passengers look out upon a Red Planet landscape speckled with lights that surround a big domed habitat.

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It's humanity's foothold on Mars, which, in the animation's universe, was doubtless established thanks largely to the efforts of Starship. The enormous vehicle will be the most powerful rocket ever launched by nearly a factor of two, according to SpaceX. And it's designed to be fully and rapidly reusable, a breakthrough that Elon Musk believes will make bold spaceflight feats like Mars colonization economically feasible.

— Starship and Super Heavy: SpaceX's Mars-colonizing transportation system

— Elon Musk says SpaceX could launch a Starship to the moon 'probably sooner' than 2024: report

— SpaceX's 1st orbital Starship looks supercool in these fueling test photos

Starship has yet to fly more than a few miles above Earth's surface, but that should change soon. SpaceX is gearing up to launch the first-ever orbital test flight of the vehicle, which could lift off as soon as next week , Musk said recently.

If the orbital trial and further flights go well, SpaceX will start working to send the stainless-steel vehicle much farther afield. NASA chose Starship to be the first crewed lander for its Artemis moon program, for example, with an astronaut touchdown currently targeted for 2025.

SpaceX has also booked several private round-the-moon missions with Starship in the coming years. And we know that SpaceX's ambitions extend far beyond Earth's natural satellite; Musk has said repeatedly that he founded SpaceX back in 2002 primarily to help humanity settle Mars and become a multiplanet species.

Mike Wall is the author of " Out There " (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter  @michaeldwall . Follow us on Twitter  @Spacedotcom  or  Facebook .

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Michael Wall is a Senior Space Writer with  Space.com  and joined the team in 2010. He primarily covers exoplanets, spaceflight and military space, but has been known to dabble in the space art beat. His book about the search for alien life, "Out There," was published on Nov. 13, 2018. Before becoming a science writer, Michael worked as a herpetologist and wildlife biologist. He has a Ph.D. in evolutionary biology from the University of Sydney, Australia, a bachelor's degree from the University of Arizona, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what his latest project is, you can follow Michael on Twitter.

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Science News Explores

Humans might be able to hibernate during space travel.

Suspended animation might one day be possible for people

In fictional depictions of suspended animation, people travel through space in a frozen state, waking up only after they have reached their destination.

HENNING DALHOFF/SCIENCE PHOTO LIBRARY

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By Tina Hesman Saey

May 24, 2023 at 6:30 am

A teenager joins a line of people boarding a spaceship. Once on board, she approaches a bed, crawls in, closes the lid and falls asleep. Her body is frozen for a trip to a planet several light-years from Earth. A few years later she wakes up, still the same age. This ability to put her life on pause while asleep is called “suspended animation.”

Scenes like this are a staple of science fiction. There’s plenty of other ways that suspended animation has touched our imagination, too. There’s Captain America, for instance, who survived nearly 70 years frozen in ice. And Han Solo was frozen in carbonite in Star Wars: The Empire Strikes Back . The Mandalorian ’s main character brings in some of his bounties cold, too.

All of these stories have something in common. People enter an unconscious state in which they can survive for a long time.

Nothing like this is yet possible in the real world, at least for us humans. But some animals and birds have their own forms of suspended animation: They hibernate. This might hold some lessons for how to put astronauts of the future into hibernation for long space flights. But for really long journeys, a deep freeze might be the best option.

Beyond sleep

“I think this is realistic,” says Katharine Grabek. She’s a biologist who co-founded a company called Fauna Bio based in Emeryville, Calif. “I think it would be done by … making ourselves as similar as we can to a hibernator.”

Hibernation may look like a deep form of sleep, but it’s not sleep. As an animal hibernates, it chills its body and slows its heart rate and breathing. Metabolism also slows. To do this, an animal must turn on and off certain genes when they hibernate. Those genes do things like controlling whether an animal burns sugars or fats for fuel. Other genes are involved in keeping muscles strong.  

Humans have many of these same genes. We don’t use them to hibernate. But turning some of these genes on or off might allow humans to do something similar to hibernation, Grabek says. Her company studies these genes and looks for drugs that can control them. Such drugs might allow people to hibernate without being really cold, she says.

Some animals’ body temperatures drop below freezing when they hibernate. Humans may not survive that chill, says John Bradford. He is the chief executive officer of SpaceWorks, a company in Atlanta, Ga. Bradford once proposed a space capsule where astronauts could hibernate. He thinks NASA could use such a capsule to send people to Mars.

Since a person probably wouldn’t survive their body temperature dropping below freezing, like a ground squirrel, Bradford suggests that people might hibernate like bears.  

Black bears cut their metabolism by 75 percent when they hibernate. But their bodies stay somewhat warm. Normal body temperature for a black bear is 37.7° Celsius to 38.3 °C (100° Fahrenheit to 101 °F). During hibernation, their body temperature stays above 31 °C (88 °F).

Hibernating humans might have to lower their body temperature only a few degrees. “We can probably keep someone in this state very safely for about two weeks,” Bradford says.

If people are like bears, hibernation may help keep bones and muscles strong. That is important in space. Bones and muscles tend to break down in low gravity. Hibernation could cut the amount of food, water and oxygen that crews need. And it could save people from the inevitable boredom of long trips in space, Bradford says.

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The deep freeze

But hibernation may not be enough to get people through decades-long trips. That’s because even champion hibernators have to rouse sometimes. Most animals come out of hibernation after a few months, Grabek says.

Making people colder might slow their metabolism even more than regular hibernation. But what if you went really cold? Or even frozen? Wood frogs in the Arctic freeze solid for the winter. They thaw out again in spring. Could they be a model for humans wanting to travel the stars?

Shannon Tessier is a cryobiologist. That is a scientist who studies the effect of extremely low temperatures on living organisms. She is looking for a way to freeze human organs for transplants. She works at Massachusetts General Hospital and Harvard Medical School in Boston.

Freezing is usually bad for organs, she says. That’s because ice crystals can rip open cells. Wood frogs can stand freezing because they have ways of preventing ice crystals from forming.

Tessier and her colleagues, though, worked out a way to supercool human livers to freezing temperatures without ice crystals forming. Right now, most organs can only be kept on ice for about 12 hours. But the supercooled livers could be stored for 27 hours . The researchers reported the achievement in 2020 in Nature Protocols . But more research is still needed. Tessier doesn’t yet know if the thawed liver will work if transplanted into a person.

Plus, freezing may not be enough for long-term space travel, she says. Wood frogs can only stay frozen for a few months. Traveling to another solar system would take many years.

In true suspended animation, all metabolism in the body would stop. One way to make that happen is flash freezing to –140 °C (–220 °F). The ultralow temperature turns tissues to glass. That process is called vitrification.

Human embryos are stored this way by quickly freezing in liquid nitrogen. “We haven’t achieved that with a whole human organ,” Tessier notes. And you couldn’t dunk a whole person in a vat of liquid nitrogen. It would kill them.

Whole bodies would need to freeze from the inside out as fast as from the outside in, she says. And they would need to rewarm just as quickly. “We don’t have the science … to do that in a way that is not damaging,” she says.

Maybe someday humans on Earth will find our own carbonite. Then we might be able to travel as frozen cargo to a galaxy far, far away.

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The Hibernator’s Guide to the Galaxy

One day in 1992, near the northern pole of a planet hurtling around the Milky Way at roughly 500,000 miles per hour, Kelly Drew was busy examining some salmon brains in a lab. Her concentration was broken when Brian Barnes, a zoophysiology professor from down the hall at the University of Alaska Fairbanks, popped by her bench for a visit. With a mischievous grin, he asked Drew—a neuropharmacologist early in her career—to hold out her hands and prepare for a surprise. A moment later, she felt a hard, furry lump deposited in her palms. It was some sort of brown rodent with dagger-like claws, curled up into a tight ball and so cold to the touch that Drew assumed it was dead. To her astonishment, Barnes gleefully explained that it was actually in perfect health.

An Arctic ground squirrel—the most extreme hibernator on the planet—can spend up to eight months a year in a torpid state. 

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The creature, an Arctic ground squirrel, was just hibernating, as it does for up to eight months of the year. During that span, the animal's internal temperature falls to below 27 degrees Fahrenheit, literally as cold as ice. Its brain waves become so faint that they're nearly impossible to detect, and its heart beats as little as once per minute. Yet the squirrel remains very much alive. And when spring comes, it can elevate its temperature back to 98.6 degrees in a couple of hours.

Drew cradled the unresponsive critter in her hands, unable to detect even the faintest signs of life. What's going on inside this animal's brain that allows it to survive like this ? she wondered. And with that question, she began to burrow into a mystery that would carry her decades into the future.

At this point, in the year 2022, no fewer than three major entities— NASA , the Chinese National Space Administration, and SpaceX —are vying to put the first human on Mars by 2040 or so. To win that race, a team must first solve a series of vexing design riddles. As an executive at SpaceWorks, an Atlanta-based engineering firm that tackles ambitious research projects for NASA, John Bradford has spent the past decade running the brutal math on one of them.

Unfortunately for the engineers trying to get humans to the Red Planet, we're a pretty high-maintenance species. As large endotherms with active brains, we burn through copious amounts of food, water, and oxygen in our daily quest to survive. All that consumption makes it extra hard to design a spacecraft light enough to reach—and eventually return from—a planet some 140 million miles from our own. Based on the eating habits of the astronauts aboard the International Space Station, for example, a crew of four will need at least 11 tons of food to complete an 1,100-day mission to Mars and back. Those meals alone would weigh nearly 10 times more than the entire Perseverance rover, the biggest payload ever to reach the Martian surface. Add in all the other life-support essentials, to say nothing of the engines and the tools necessary to set up camp, and the weight of a fully fueled Mars-bound ship could easily exceed 330 tons as it departs Earth's atmosphere—more than two fully grown blue whales. It's nearly impossible to see how a vessel that massive could generate the power necessary for its entire round-trip journey.

The obvious solution to this problem—at least to anyone who's read any Arthur C. Clarke novels or watched Stanley Kubrick's 2001: A Space Odyssey —is to slow the metabolism of crew members so they only need to ingest a bare minimum of resources while in transit. In 2001 , astronauts lie down in sarcophagus-like hibernation pods, where their hearts beat just three times a minute and their body temperature hovers at 37 degrees Fahrenheit. Bradford has devoted a huge chunk of his 21-year career at SpaceWorks to investigating a question that Kubrick had the artistic license to ignore: How, exactly, can we safely power down a human body so it's just one step removed from death, then revive it on demand?

Early on in his research, Bradford glimpsed some promise in therapeutic hypothermia, a medical technique in which people who have experienced cardiac arrest are chilled—typically with intravenous cooling fluids—until their internal temperature reaches as low as 89 degrees Fahrenheit. This decreases their metabolism so much that their cells can function on roughly 30 percent less oxygen and energy—a lifesaver for a damaged body that's struggling to heal amid reduced blood flow. Patients are usually kept in this hypothermic state for only a day or two, mostly because the cold triggers intense shivering that must be controlled with powerful sedatives and neuromuscular-blocking drugs. But Bradford identified a few rare cases in which patients were kept hypothermic for as long as two weeks. “And we started asking, why can't you do that for longer?” he says. “How long can you sustain that comatose-like state?”

Bradford was wary of going public with his curiosity, fearing he'd be branded a crank for suggesting astronauts be put on ice—a concept uncomfortably similar to the one touted by the dubious cryonics industry. But in 2013 he persuaded NASA's Innovative Advanced Concepts program to fund a project assessing the feasibility of “human torpor.” His successful pitch centered on the potential weight savings: He estimated that if astronauts could be kept frigid for the bulk of their trip to Mars, the mass of their life-support resources could be cut by as much as 60 percent. Bradford also hypothesized that torpor could help astronauts fend off a number of serious health hazards, ranging from radiation to the psychological perils of extreme boredom and isolation. (“You're in the blackness of space, you don't have real-time communications,” he says. “A lot of people will say, ‘Oh, I'll just read a lot of books.’ But I think that will get old quick.”)

Yet as Bradford and his team dug into the minutiae of therapeutic hypothermia, they steadily soured on the technique. There seemed to be no getting around the fact that the drugs used to control shivering also stop respiration. Torpid astronauts would have to be intubated, meaning they'd have to spend weeks or months breathing through tubes shoved down their tracheas. Bradford also balked at the number of needles required to keep the IV fluids flowing, a situation that seemed likely to increase the odds of infection.

The dream alternative was for astronauts to be able to swallow a pill, then lie down for a long and chilly slumber during which they could breathe on their own. It seemed a fantastical proposition, but aspects of it struck Bradford as familiar. There are, after all, scores of species that go torpid every winter, drifting into an unconscious state that drastically squelches their bodies' cravings for food and air. When they rapidly whirr back to life in spring, these creatures show no signs of suffering from muscle atrophy, malnourishment, or other ailments that might be expected to stem from lengthy spells of idleness. Bradford suspected there might be useful wisdom to be gleaned from understanding how such animals switch into low-power mode when their environments turn harsh.

And so Bradford began to seek counsel from the small community of hibernation researchers, scientists devoted to studying the bears, bats, and lemurs for whom regular torpor is a fundamental aspect of existence. In recent years, these researchers have been piecing together the molecular changes that occur when certain species ratchet down their metabolism. And since so many hibernators are our close genomic cousins, there is good reason to believe that we can tweak our brains and bodies to mimic what they do.

By then, the University of Alaska's Kelly Drew had been researching the Arctic ground squirrel, the most extreme hibernator on the planet, for more than 20 years. When Bradford first connected with her in 2015, she was fresh off a major breakthrough—a vital first step toward giving humans the power to turn themselves off and on at will.

When Drew left Alaska after college in 1982, she assumed she'd never live there again. She had moved to Fairbanks in her teens so that her father, a prominent soil scientist, could take a professorship at the state's flagship university. Though Drew loved Alaska's desolate beauty, she had her sights set on a scientific career that wasn't linked to the wilderness. So at the age of 22, she decamped to New York to earn a doctorate in pharmacology, then to Sweden for a postdoc studying how brain metabolism affects human behavior.

But shortly after her daughter was born in 1990, Drew and her husband, whom she'd met in college, felt the gravitational pull of their home state. Like so many overwhelmed new parents, they suddenly warmed to the idea of being close to family. So even though Drew didn't have a job lined up, she agreed to return to Fairbanks—a decision that bewildered her Swedish coworkers. “I mean, they seriously just laughed and went, ‘Well, that's the end of your career,’” Drew recalls.

Kelly Drew has been studying the brains of hibernating Arctic ground squirrels since 1992.

It didn't take long for her to conclude that the naysayers might have been right. She had assumed she'd be able to snag a few grants to continue the work she'd been doing in Sweden, but no one seemed eager to dole out money to a young, unaffiliated researcher based in a remote northern outpost. With each rejection, she became more certain that her homecoming had been a horrendous mistake.

After a year's worth of failures, Drew finally landed a small National Science Foundation grant with a very Alaskan twist: She was commissioned to study the neurochemistry of coho salmon. She used that gig to talk her way into borrowing a few square feet of lab space in the university's Institute of Arctic Biology—a toehold back in academia that she hoped would lead to bigger things.

It did, though in a most unexpected way. It was during the salmon study that Brian Barnes first plunked an Arctic ground squirrel into Drew's hands. Instantly curious about what was taking place inside the critter's brain, a topic that had scarcely been researched, Drew began to examine hibernating ground squirrels using microdialysis, a technique in which tiny tubes are inserted beneath a living creature's skull to harvest samples of neural chemicals. The procedure normally causes scarring in the places where the tubes come in contact with the brain. So Drew was stunned when she couldn't detect any such damage after performing microdialysis on the torpid squirrels.

“You couldn't even find where the probe had been,” she says. “And so we started talking about hibernation as being a very protected state—it really seemed to protect the brain from injury.” This revelation made Drew think there could be tremendous value to replicating that state in humans.

For a brief moment early in the Cold War, hibernation research flourished in the United States. With the federal government fixated on besting the Soviet Union at every turn, there was plenty of money sloshing around to fund scientists who claimed their work could give the US any sort of biological edge. Many of these researchers passed through military facilities located in or near the Arctic, where there was ready access to all manner of animals that have evolved the means to power down for winter.

Among this group of scientists was Raymond J. Hock, a zoologist who'd written his doctoral thesis at Cornell University about the metabolic rates of hibernating bats. In the mid-1950s he wound up at the Arctic Aeromedical Laboratory in Fairbanks, where Air Force scientists were scrambling to make American soldiers immune to cold. (In one ethically shaky experiment, the lab's personnel paid several Indigenous inhabitants of Chilean Patagonia to wear temperature sensors and ventilated plastic hoods while they slept in freezing canvas tents.) Hock developed a keen interest in bears during his stint in Fairbanks, and he lamented how little was known about the changes in the animals' metabolism during hibernation. So he mustered the courage to creep into the sleeping bears' dens and stick thermometers in their rectums, a gambit that allowed him to assess just how much their internal temperature declined during their annual torpor.

In 1960, Hock published a paper entitled “Potential Application of Hibernation to Space Travel” that offered the first sober, detailed look at how the budding American space program might benefit from the research he was helping to pioneer. Hibernation was within our grasp, he argued, the major hurdle being the human heart's sensitivity to rapid temperature fluctuations. “The hibernators have learned how to do this, and several laboratories are currently working on ways to avoid it in man,” he wrote.

Hock also noted that hibernation has the potential to slow aging. “A hibernator, with its greatly reduced annual energy expenditures, will live longer than a non-hibernating mammal of the same body size,” he asserted. If humans, like bears, were able to maintain an internal temperature about 13 degrees colder than normal, he estimated that “aging should occur at half the normal rate during this period.”

In the early 1960s, while working at UCLA's White Mountain Research Center in California, Hock and his colleagues subjected hibernating marmots to sudden blasts of extreme cold. They discovered that the animals' brown fat—a type of tissue humans also possess—generated heat in response to the shock. Hock's team saw this as the key to enabling humans to survive frigid torpor: We needed to unlock brown fat's innate power to keep our internal organs functioning as our metabolism slowed.

But Hock died in a tragic accident in 1970. And as the Cold War matured, hibernation research fell out of fashion. With funding from the Pentagon and NASA at an ebb, biologists came to think of the field as a backwater. Since it takes a full year to gather data about an annual hibernation cycle and then compare it to an animal's normal activity, the research tends to be agonizingly slow. “It's a gamble for a young professional scientist,” says Barnes, who introduced Drew to ground squirrels in 1992 and was the Institute of Arctic Biology's director from 2001 until 2021. “You're not going to have the same number of publications as you would in a different field.”

But Drew, whose kindly demeanor belies her tenaciousness, was so captivated by the Arctic ground squirrel that she plunged into hibernation studies with zeal. She took to camping out on the North Slope each summer so she could trap squirrels by the dozen for her lab. (Accustomed to lives of deprivation, the animals are hopeless suckers for the carrots she uses as bait.) She secured funding from the US Army's research office, selling them on the idea of saving badly wounded soldiers by safely and rapidly cooling their bodies on the battlefield. To make that happen, she needed to identify the chemicals that trigger hibernation in Arctic ground squirrels, then test whether those might have a similar effect in humans.

Drew, who became an assistant professor at the Institute of Arctic Biology in 1993, initially hypothesized that gamma-aminobutyric acid, a neurotransmitter commonly known as GABA, was chiefly responsible for sparking hibernation in her squirrels. GABA is integral to inducing sleep, the state in which a non-hibernating animal's metabolism is typically at its lowest. (Humans' normal metabolic rate falls by 15 percent while we doze.) And hibernation, for all its complexities, is essentially just a very deep form of sleep—a state in which respiration is lowered, appetite is suppressed, and waste expulsion is controlled. (Bears, for example, typically do not defecate or urinate throughout their winter torpor.)

But when Drew dosed her squirrels with GABA and an array of related chemicals, none brought about any sort of stable, long-term torpor. Years slipped by in this frustrating manner: Drew celebrated her 40th birthday, mentored dozens of graduate and undergraduate students, and watched her daughter become a teenager while her efforts to find the molecular key to hibernation remained mostly stuck in neutral.

In 2005, a dozen or so years into Drew's research on the squirrels, an undergraduate chemistry major named Benjamin Warlick joined her lab as an assistant. One of his duties was to scour databases in search of fresh ideas about the chemicals that might activate ground-squirrel hibernation. Among the many papers he unearthed was an obscure one from Japan's Fukuyama University entitled “Phase-Specific Central Regulatory Systems of Hibernation in Syrian Hamsters.” Though the main text was entirely in Japanese, a language that Warlick doesn't know, the brief abstract was in English. That paragraph mentioned that the authors had snapped their hibernating hamsters out of torpor by administering a drug that blocked the A1 adenosine receptor in the animal's cells. Though that was the opposite of what Drew was trying to accomplish, Warlick flagged the paper for his boss as worthy of a glance.

Two years passed before Drew got around to having the document translated in full. But when she finally read the English version in 2007, an idea struck her: If blocking the A1 adenosine receptor caused hibernating hamsters to stir, perhaps activating it in her squirrels would induce torpor.

Sure enough, when she dosed her ground squirrels with CHA, a drug well known for stimulating the A1 adenosine receptor, the animals promptly cooled down and began to hibernate. This happened only if they received the drug during the winter months, a sign that something else was going on in the squirrels' brains that kept them on an annual hibernation schedule. Still, Drew was encouraged enough to begin working on a paper for The Journal of Neuroscience about the drug's mechanism of action in the Arctic ground squirrel.

As intrigued as she was by CHA's effects in her squirrels, however, the drug had a major downside: She had to inject it directly into the animals' brains. When administered intravenously, CHA is notorious for affecting the A1 adenosine receptors in the heart, slowing the organ until it stops beating altogether. As a result, CHA seemed like it could only ever be of limited use in humans: It's rarely advisable to stick needles into someone's brain, particularly outside of a hospital setting.

In 2011, while putting the finishing touches on her Journal of Neuroscience paper, Drew had a poster made of all the data she hoped to include in the article. She hung it in the hallway outside her lab so she could review the numbers whenever she walked by. But as she paused by the tables of data one day, she was struck not by how much she'd accomplished, but by how much knowledge still eluded her. Nearly two decades after Barnes had first placed a frigid squirrel in her hands, she hadn't devised a way to turn her esoteric expertise into the safe and effective drug she'd envisioned. What should have been a moment of triumph instead felt like a minor defeat.

And then in the midst of her melancholy, a thunderbolt hit: What if Drew could combine the CHA with another drug that would block its effect on the heart, but not the brain? CHA is what's called an agonist, meaning it stimulates receptors; a drug that blocks them is an ant agonist. What Drew needed, she realized, was an A1 adenosine antagonist with molecules too large to cross the permeable blood-brain barrier.

“If you think of the body as a color map, and of agonist as red, then the agonist—the red—is everywhere. It's stimulating all the receptors,” Drew explains. “Now, you don't want it to stimulate the heart receptors, so you have to block those receptors. Now, think of the antagonist as blue. So you put that in the body, but it doesn't get into the brain, right? So the rest of the body is purple, but the brain is still red.”

There was already an extensive literature on A1 adenosine antagonists, so Drew had several good candidates to choose from. She ultimately settled on 8-(p-sulfophenyl)theophylline, or 8-SPT, which is closely related to one of the main ingredients in black tea. She melded this with CHA into a drug cocktail that was injected into the abdomen. To test this combination, Drew then launched a series of experiments on rats. She would stop the rats' hearts, then revive them by performing CPR. Once pulled back from the brink of death, the rats were then either made hypothermic with the CHA/8-SPT combination or left to heal with their metabolism at a normal rate. The rats that received the cocktail fared much better than the ones that didn't. And perhaps most significantly, the treated rats suffered no ill effects from having their thermostats turned way down by the drug. There was no shivering, and thus no reason to give any narcotics that might interfere with their breathing.

By 2014, Drew had achieved such excellent results in her experiments on rats that she applied to patent her invention: “Methods and compositions for the treatment of ischemic injury to tissue using therapeutic hypothermia.” The first illustration in the application is a photograph of an Arctic ground squirrel curled into its trademark hibernation pose, a nod to the small moment in 1992 that had altered the course of her life.

From an ordinary familiarity with sci-fi movies like 2001 and Planet of the Apes , Drew was always vaguely aware that her work might attract interest from the space-exploration industry. So she wasn't terribly surprised when someone from SpaceWorks reached out to her in February 2015. The firm had just secured a second tranche of NASA funding to press forward with its human-torpor research, and John Bradford invited Drew to become his company's chief hibernation consultant.

SpaceWorks arranged for Drew and Matthew Kumar, an anesthesiologist at the Mayo Clinic, to test the CHA/8-SPT cocktail on pigs. The drugs steadily and safely lowered the animals' internal temperature to between 86 and 90 degrees Fahrenheit—not quite as chilly as the state doctors can achieve using intravenous fluids on humans, but close. In his summary of the experiment, Bradford wrote that the cocktail “could lead to a torpor induction protocol that does not require any active cooling [and] eliminates the need for pharmacological sedation to suppress shiver response.”

Drew was not the only hibernation researcher shifting her focus to Mars around this time. In 2017, a University of Colorado biologist named Sandy Martin, who had spent her career building a tissue bank containing samples from various hibernating species, was approached by students organizing a one-day symposium on space travel. They urged her to talk about whether her life's work could be used to facilitate human torpor on long voyages. “I had never thought seriously about it,” Martin says. “I mean, it's always in the back of your mind as a hibernation researcher, what the applications might be, but that was never the motivation for me. My motivation was, ‘This is a profound evolutionary adaptation.’ I mean, for a mammal to be so plastic in terms of body temperature, and the ability of cells to survive hypoxia and temperature swings, all that is just so profound.” In preparing for her talk, Martin unearthed an older SpaceWorks paper that advocated using IV cooling fluids to place Mars-bound astronauts in torpor. She forwarded the paper to her daughter, an emergency medicine resident who dismissed SpaceWorks' proposal as “ridiculous” due to the pesky shivering problem.

“I thought, ‘What we need to do is figure out how hibernators do this, because they do it so beautifully and so naturally and without harm,’” Martin recalls. “And they don't need intubation, and they don't need feeding tubes.” She and her daughter began working on their own paper, proposing several promising avenues of inquiry based on Martin's genomic analysis of the thirteen-lined ground squirrel, a close relative of the Arctic ground squirrel. One was to investigate further a receptor called TRPM8, which plays a crucial role in helping thirteen-lined ground squirrels thermoregulate during hibernation.

In March 2018, NASA invited Drew, Martin, and a handful of other luminaries from the hibernation community to a two-day conference in Mountain View, California—an event billed as the agency's first-ever “space torpor workshop.” The meeting was an opportunity for the biologists to make the argument that, if provided with sufficient backing, they could help humans achieve at least some level of true hibernation in the next 10 to 15 years—a timeline that dovetailed nicely with NASA's plans to send humans to Mars in the late 2030s or early 2040s.

Speaking to NASA officials at the workshop, Martin emphasized that the pervasiveness of hibernation among mammals suggests humans can achieve it too. There are three types of mammals: the egg-laying monotremes, such as the platypus; the marsupials, which carry their undeveloped offspring in pouches; and the placentals, the category that includes us. “All three of those branches have hibernating species,” Martin says. “The most parsimonious explanation for that is that our common ancestor was a hibernator.” Assuming that's the case, preparing our species to deal with the physiological stresses of torpor may simply be a matter of altering genes we already possess.

Four months after the NASA workshop, SpaceWorks published the final report from the second phase of its human-torpor project. The 115-page document is frank about the many challenges that lie ahead: Bradford and his coauthors admit that little to nothing is known about how hibernation might affect an astronaut's cognitive abilities, for example. But the report also asserts that, based on the current pace of research, NASA could begin testing hibernation technologies such as Drew's drug cocktail on human subjects as early as 2026. Judging by investments that NASA has initiated in recent months, the agency seems intent on making that happen.

NASA hasn't just started to accept that torpor is essential to making spaceships lighter. The agency has also come around to Bradford's view that it may help astronauts avoid some of the physical hardships of long-haul space travel. One of the great unknowns about the mission to Mars, for example, is whether humans can endure the ravages of galactic cosmic rays, the remnants of the Milky Way's celestial violence. Once a spacecraft travels beyond Earth's protective magnetosphere—which orbiting craft like the International Space Station stay well within—there's no real way to dodge these cancer-causing particles, and scientists have yet to find a malleable, lightweight material that can shield against them. But if human cells can be made less active, they may develop significant resistance to radiation. In a 1972 experiment, for example, scientists found that ground squirrels that were irradiated while hibernating had a much higher survival rate than their fully conscious peers.

“The hypothesis is that if you reduce the metabolism in the cells, then you would also reduce the damage from radiation,” says Emmanuel Urquieta, chief medical officer for the Translational Research Institute for Space Health, a NASA-sponsored program based out of Baylor University's College of Medicine. “So you can give the cells a little bit more time to start repairing themselves from radiation exposure.”

In August 2021, Urquieta's institute awarded $4 million to researchers interested in furthering the science of human torpor. One of the recipients is now examining the fossilized remains of an extinct human species that may have hibernated in the caves of northern Spain some 430,000 years ago. Another awardee is trying to establish the ideal temperature at which humans can hibernate without causing undue physiological stress. And Clifton Callaway, a professor of emergency medicine at the University of Pittsburgh, is deepening his investigation into drugs that might be used as part of a suspended-animation system on long-haul space flights.

Like Bradford, Callaway's early interest in human torpor grew from his curiosity about therapeutic hypothermia. He has long wanted to use the technique to help not just survivors of full-blown cardiac arrest but also people who walk into the ER exhibiting the early signs of heart attacks. To help make therapeutic hypothermia a realistic option for such patients, Callaway looked for drugs that can prevent shivering without knocking vital organs out of commission. Just before the Covid-19 pandemic hit, he obtained some encouraging results with dexmedetomidine, a mild sedative used in anesthesia. “It worked well enough that we actually said, ‘God, you really could use this in astronauts,’” he recalls.

Pure dexmedetomidine probably doesn't have much of a future aboard spacecraft, since its sedative effects last only 30 minutes and it must be administered intravenously. But there are a host of closely related drugs that Callaway is testing on human subjects, hoping to find one that can be delivered via pill or patch. Next year he plans to expand his work to assess how well our species can rebound from an extended period in a low-metabolic state.

“Our master project is to take eight or 10 people and have them do a torpor for five days,” Callaway says. “I want them to sleep 20 hours a day, have a slightly lower body temperature, use less oxygen and consume fewer calories, and make lower carbon dioxide for five days. And we're going to do a whole bunch of testing before they start and after they finish to see, you know, what's the hangover?”

Callaway does not yet know how he plans to make his test subjects torpid, but he is well aware of the innovations coming out of Kelly Drew's lab in Alaska. Drew paid him a visit in 2019 and opened his eyes to the possibilities of taking inspiration from animal hibernators. “One lesson I've gotten from the physiologists studying hibernation is that we would be very naive to think that we're going to find one single drug that just lets an animal or a person go into hibernation,” Callaway says. “I imagine in 10 years, the answer we'll be looking at will be maybe one of the drugs in the class I'm studying right now, in combination with a drug that Dr. Drew is studying, and then another drug some other sleep researcher is studying. It'll be that cocktail of drugs that'll be most likely to provide astronauts with a safe sleep for a long distance.”

Callaway doubts that when those astronauts sleep they'll ever get as cold as the Arctic ground squirrel or have metabolisms as low. But he notes that bears are pretty effective hibernators too, and they reduce their internal temperature by only a few degrees while snoozing through a winter. “In this decade,” he says, “we can replicate that.”

Sometimes Drew cannot believe that, at the age of 63, she has devoted nearly half her life to trying to determine how a 3½-pound rodent shuts down for the winter. She counts herself fortunate to have been able to crack problems at such a meticulous pace. “When you talk to people in industry, I mean, they just, they would never tolerate this,” she told me, with a self-deprecating chuckle.

But thanks to university-based researchers like Drew who've solved some of the fundamental mysteries of hibernation, the private sector is taking notice of its potential. When the University of Colorado's Sandy Martin retired last year, she arranged for her bank of hibernator tissues to be licensed to a former student, a computational biologist named Katie Grabek. Grabek then cofounded FaunaBio, a Silicon Valley startup that aims to improve treatments for heart and lung diseases by discovering why hibernators can survive stressful events—particularly the abrupt shocks to internal organs that occur during cooling and rewarming—that would kill most humans.

“These animals, when they arouse from torpor, it's very similar to having a heart attack,” Grabek says. FaunaBio wants to identify the molecular compounds that hibernators use to prevent or repair cellular damage, in the hope of developing pharmaceuticals that can help cardiac patients.

But if hibernation does indeed become a realistic option for humans, even those of us in decent shape may find it tempting. Induced torpor seems to offer a roundabout path to realizing at least a couple of transhumanist dreams. Like life extension, perhaps—provided you're not purely bent on extending your conscious life. As Raymond J. Hock noted in 1960, hibernation really does seem to offer a fountain of youth. Earlier this year, for example, a team at UCLA found that yellow-bellied marmots, which hibernate for as much as two-thirds of every year, possess much more robust genetic material than might be anticipated based on their chronological ages. “The molecular and physiological responses required for an individual to successfully hibernate may prevent aging,” the researchers wrote in Nature.

In an odd way, hibernation may also turn out to be the only remotely attainable form of time travel. In a satirical story from 1850, Edgar Allan Poe imagined that the ancient Egyptian practice of mummification was just such a technology. When the story's protagonists accidentally revive a mummy, the awakened Egyptian explains that his civilization's historians sometimes lived their lives “in installments.” They would hibernate for a few hundred years, then arouse to correct the record about the era from which they'd originated—a method for “preventing our history from degenerating into absolute fable.” Of course, no one today is keen to develop a hibernation cocktail that can induce torpor for centuries. But a biological fast-forward button that would allow someone to skip months or more into the future could have its uses—or, at the very least, appeal to a certain kind of adventurer.

As for myself, what I find most alluring about hibernation is its potential to offer a brief holiday from the constant din of my own thoughts. In a time of exhausting overstimulation, anxiety, and dread, I find myself wondering what it would be like to switch off for a week or two. In his novelization of 2001 , Arthur C. Clarke depicted one of his main characters as longing for the psychological liberation of torpor: “Sometimes Bowman, as First Captain of Discovery , envied his three unconscious colleagues in the frozen peace of the Hibernaculum. They were free from all boredom and responsibility.”

Then again, the vulnerability of the hibernator is a perennial theme in science fiction. In 2001 , the three astronauts who spend the film sealed in hibernation pods are unceremoniously murdered by HAL 9000, their ship's sentient operating system. Countless other works of sci-fi focus on the shock and social dislocation that long-term hibernators experience when they emerge into worlds that have gone haywire in their absence. Even if we go under for only a few months in order to accomplish a worthwhile endeavor like reaching Mars, reentry into consciousness is bound to be a complicated affair. Arctic ground squirrels snap back to their old selves within hours of warming up. But that might not be the case if they were blessed with human self-awareness.

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Zapping a rodent's brain can put it into suspended animation. Scientists want to one day use the same technique for humans traveling to Mars.

• Scientists have zapped mice and rats into a suspended-animation-like state called torpor. 
• The state was induced by beaming ultrasound waves into a precise spot in the rodent's brains. 
• This technique could one day be used on humans for space travel and medical purposes.

Scientists have been able to induce a torpor state in mice and rats using ultrasound, bringing them a step closer to finding a way to induce suspended animation in humans. 

Space agencies like NASA and the European Space Agency ( ESA ) are eagerly awaiting science that artificially induces torpor or hibernation-like states in animals. 

They hope this could one day save on energy and costs of long-haul space travel to planets like Mars.

The latest study, published in the peer-reviewed journal Nature Metabolism, found researchers were able to induce torpor in mice and in rats using ultrasonic waves targeting a precise part of the animals' brains. 

"If successfully demonstrated in humans, this technology holds significant potential for medical applications, particularly in life-threatening conditions such as stroke and heart attacks," lead study author Hong Chen, a professor of biomedical engineering at Washington University, told Live Science .

"We could envision astronauts wearing a helmet-like device designed to target the hypothalamus region to induce a torpor-like state," she said.

Tiny helmets zap the rodents' brains

Torpor is a state of suspended animation whereby animals may look like they are going to sleep, but they are actually drastically reducing their metabolic activity, usually in response to extremely adverse conditions. 

Scientists had previously found that torpor can be triggered by injecting a chemical into a precise part of the brain that controls the central nervous system. But Chen and colleagues were interested to see if there was a non-invasive way to induce that state, without physically breaching the skull. 

Mice and rats were fitted with tiny helmets to send ultrasonic waves to the brain. The scientists observed that these waves were effectively able to push the rodents into a state of torpor.  

For about an hour after the ultrasound pulse, the mice's body temperatures and metabolism dropped, a state similar to torpor seen in nature. The mice's average body temperatures dropped by up to 6.25 degrees Fahrenheit (3.5 degrees Celsius) and their heart rate and oxygen usage dropped as well. 

The rats' body temperatures also dropped, though to a lesser level, up to 3.57 F (2 C). 

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The fact that this state was triggered in rats is encouraging, as these rodents "do not naturally enter torpor, suggesting the possibility that similar effects could be induced in humans," the scientists said in the study.  

This technology could one day be used to make space travel more economical

Space agencies are keeping a close eye on this type of research . If they were able to crack the science of suspended animation, it could make space travel safer and cheaper, especially for long-haul flights like the 16-month-long round trip to Mars.

A single astronaut eats about 30 kilograms (66 pounds) of food and water a week, but their consumption could drop by 75% in suspended animation, per the BBC. Astronauts would also need much less space to roam around, so the rocket wouldn't need crew quarters.

Taken together, these cuts could save several tons of mass, a crucial saving when each pound adds weight to an already hefty rocket, ESA found in a 2019 study.

Inducing a hibernation-like state also has health benefits. Studies suggest astronauts would be at lesser risk of substantial muscle and bone density loss and protected from the worst effects of exposure to cosmic radiation. It could also protect the astronauts' mental health, as nobody knows what happens to human minds after being away from Earth for that long.

Hibernation in space would be "nowhere near as extreme as what we see in the movies," John Bradford, president and CTO of SpaceWorks Enterprises, previously told CNET. Spaceworks received several funding rounds from NASA in 2016 to develop a space hibernation concept. 

For Spaceworks, astronauts would be induced into torpor for 14 days at a time and woken for three or four days. That way, there would always be an active astronaut on shift to monitor proceedings. 

Scientists are getting closer, but aren't quite there

The rapid progress in the basic science to support this innovation is encouraging. 

One avenue to induce suspended animation is to cool the body down dramatically. In fact, surgeons are already using deep hypothermia — cooling the body temperature to under 95 degrees Fahrenheit (35 celsius) — to stop the blood during particularly tricky cardiac surgeries, though this should be done for more than 20 to 30 minutes. 

Other studies, like this recent one, suggest hacking the brain's dormant torpor mechanism to induce this state. Previous studies had suggested torpor could be induced with drugs, but the advantage of the approach in this recent study, is that it is noninvasive, precise, and safe, scientists said in the study. 

"As far as we know, there is nothing unique about  homo sapiens that would prevent our species from hibernating, and I believe the capacity is there but it needs to be unlocked," Vladyslav Vyazovskiy, professor of sleep physiology at the University of Oxford, told the BBC.

"To me, the real question is not whether we can hibernate, but how… How do neurons in the hypothalamus 'know' that it is time to hibernate? Who tells them? This is the real question," he said.

Nevertheless, most of the research into long-ranging suspended animation is still only being done on animals, and we're likely still a long way away from testing it on humans.

"Further research is still required to determine the safety and feasibility of this approach in humans," Chen told Live Science. 

Watch: Newly elected Arizona Sen. Mark Kelly and his twin brother took part in a groundbreaking NASA experiment for 4 years. Here's what we learned from it.

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Space Nebula In Outer Space

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The starry night sky two huge planet (moon). In the distance shines bright yellow star (sun). Under these the desert landscape of an alien planet. Hills, rocks, sand. Over the horizon a thick gray mist. The sky slowly floating clouds. The surface of

Back view of traveler with backpack walking along path

Realistic Milky Way 3D space moving stars Universe slow motion

Shocked traveler walking away isolated on yellow

Medium shot of astronaut giving thumb up

Pretty young woman carrying wheeled bag, opening it on floor and walking away

Front view of traveler standing and eating sandwich outside

A spaceship in orbit above planet earth 4k

Low angle view of tourist walking and listening to music outside

Looping Space Flight Through a Galaxy

Happy traveler in sunglasses holding suitcase isolated on yellow

Sunrise on Earth from Space

Businesswoman in suit drinking coffee in hotel

Animation of the International Space Station (ISS) in Orbit above Planet Earth. Contains public domain images by NASA.

Cheerful woman reading travel newspaper in hotel room

Cheerful housekeeper looking at camera in hotel room

Close up shot of astronaut looking around on the Moon

Smiling traveler hugging suitcase isolated on yellow

A Rotating Spiral Galaxy in Cosmos - Space Travel Through The Stars

Side view of man sitting and chewing grass on hill

View of planet Earth from the Moon. Realistic 4K UHD animation of the solar system.

Young, focused man reading business newspaper while resting in hotel room

Sunrise on Earth from Space Seen from Space

Young housemaid wearing rubber gloves in hotel room

Smiling businesswoman talking on smartphone in hotel room

Sunset over Alien Planet. Bright sun in a halo quickly sits down at the misty horizon. On a dark starry sky big moon. High snow-covered rocks with sharp peaks stand among the foggy lakes.

Happy traveler laughing at camera isolated on yellow

Upset businessman sitting on bed with clenched hands in hotel room

Alien Planet and Nebula. There are blue stars in the dark sky, a beautiful multi-colored nebula. A planet flies from the depths of space and is illuminated by a bright radiant blue star.

Sad traveler showing stop gesture at camera isolated on yellow

Time lapse of pretty young woman packing summer clothes in yellow wheeled bag on floor at home