Ever since we have come to the realization that there are other star systems and planets out there in the void of space, we as a species have longed to go out to them. It is an extension to a seemingly almost innate desire we have had since time unremembered, to go out over the horizon into the dark places of our maps and conquer new realms and domains. The problem is, space is really, really big. Let’s look at the closest star to Earth, which is Proxima Centauri, which is about 4.25 light-years away, around 25 trillion miles (40 trillion km). To put it into perspective if we were to take the fastest Earth spacecraft ever made, which would be the Parker Solar Probe, with a top speed of 450,000 miles (724,000 km) per hour, it would still take us about 6,633 years to reach that star. Even if we could somehow reach the speed of light, which we can't, it would still take us 4.5 years to get there, which is a pretty long trip. With even the moon you could fit all of the planets in the solar system between us and still have space to spare, and it takes us days to reach it. The main hurdle to interstellar travel is the speed of light, which through a vacuum is exactly 299,792,458 meters (983,571,056 feet), or 186,282 miles, per second. According to Albert Einstein's theory of special relativity, on which much of modern physics is based, that’s it, that’s the fastest anything in the universe can go. This is not just a speed bump, but more of a brick wall, so is there some other way? One idea that has been often utilized in science fiction is that we might be able to get into some sort of hypersleep pod and just go to sleep in a state of suspended animation, but just how realistic is this notion? Let's take a look.
Besides the extreme distances involved with space travel and the amount of time it would take to reach our destination, there is also the problem of food and supplies for such a journey. How would we be able to pack for years’ worth of food, water and other necessities? The logistics would be mindboggling even for a trip to Mars, let alone another star system. There is also the problem of the amount of radiation that astronauts are exposed to in interstellar space outside the partial protection of the Earth's magnetic field, which can result in cell death, radiation sickness or cancer, as well as the mental and psychological challenges of these space travelers being cooped up on a ship for years at a time. How would someone mentally be able to handle long years in the lonely dark void of space in a confined space? It seems like there has to be a better way if we are ever seriously going to travel to other stars and planets beyond our solar system. Of course there is the idea of somehow breaking past the pesky barrier of the speed of light, but another idea that has been seriously considered in recent years is that we might be able to just sort of sleep through the whole way and wake up on the other side.
The idea that we could get into some sort of pod or apparatus and sleep our way to the stars is not new in the realm of science fiction. Countless science fiction stories and movies have featured astronauts doing this in some form or another, usually depicted as going into some kind of suspended animation within a machine of some sort and being revived upon reaching their faraway destination to go about their business. The main idea is that if we could go into a kind of suspended state we could not only avoid the logistics of food, water and supplies, but also sidestep the problem of extreme boredom and mental anguish that would be inherit to such long, grueling journeys, making long-duration exploration more feasible. In recent years, this idea has emerged from mere fiction to become an area that has been seriously considered and pursued by scientists, and there has been some promise that it could one day become a reality.
Scientists call it “torpor-induced hibernation,” and it entails an induced state that reduces the metabolic rate of an organism to much lower levels than usual or even approaching zero. This is seen in the natural world in various species of animals that hibernate in order to preserve energy during harsh times of cold or food or water scarcity, during which time the organism’s heart rate, breathing and other vital functions are lowered dramatically, and their body temperature often reaches ambient temperature, with many such animals seeing a decrease in metabolic activity of up to 98%.. Many types of Tardigrades, frogs and reptiles do this, but mammals as well, with perhaps the most well-known example being bears, which although not truly hibernating in the strictest sense of the word will nevertheless slow their body down to a level that allows them go up to 6 months in an immobilized state without food. The idea is that if we can somehow simulate this state in human beings, then it could be the key to space travel in the future. You would just go to sleep and wake up at your destination, with no concept of all the the years or even decades that have passed.
One of the ideas for how to achieve this is based on a concept we have known about since as early as the 1960s, when doctors began experimenting with what is called “therapeutic hypothermia,” in which a patient is intentionally radically cooled down to slow circulation and reduce oxygen requirements before heart surgery or other traumatic operations, and to lower their metabolism just enough to reduce tissue oxygen requirements and allow the brain and other vital organs to recover. Surgeons have also long employed techniques for inducing cooling and metabolic suppression in victims of extreme trauma such as heart attack, stroke, gunshot wounds, profuse bleeding, or head injuries resulting in brain swelling. The whole concept is based on the idea that if you get cold fast enough before the heart stops, the vital organs, particularly the brain, can tolerate cold without blood flow for a time. This has been seen outside of medical procedures in some pretty dramatic ways, such as people who have fallen through ice or been buried in snow and frozen to the point of near death, only to be miraculously revived with few to no side effects. However, there are some problems with the idea.
One of the most glaringly obvious problems is that, although induced hypothermia has been used for decades in the surgery room, it is one thing to lower a patient’s metabolism for an operation for a short duration and quite another to put someone under for months or years at a time. There is simply very little understanding on how this could be achieved and what affect this would have on our physiology, and no way of knowing if a person could ever be revived from such a thing to a totally operational level. Although this has been documented in some extreme cases, we have no idea why certain individuals have been able to be revived from what would normally be catastrophic hypothermia or what processes or conditions facilitate it, let alone how to recreate the effect to any appreciable degree. Another problem is atrophy of the muscles, bone loss, and organ degradation. Unlike hibernating animals, if a human is bedridden and immobile for 90 days they will typically lose around half of their strength and muscles mass, as well as lose bone density, so how do we get around that? Although bears and other animals can hibernate for long periods with minimal muscle loss, how do we mimic that in humans? Is it even possible at all? No one really knows. These are just some of the many hurdles to making human hibernation in space a reality, and there have been some findings that have shown it might never even be possible at all.
A new study into the feasibility of human hibernation in space was conducted by researchers at the Millennium Institute for Integrative Biology, in Chile, whose aim it was to unravel the relationship between body mass and energy expenditure in animals that hibernate, namely mammals like us. What they found was that only smaller mammals that hibernate, like ground squirrels, hedgehogs, and bats, showed any appreciable energy savings, while an animal closer in size to a human saw little to no energy savings compared with just regular sleep or rest, and in some cases even experienced an energy loss. For instance, it was found that a 400-pound grizzly bear actually has negative energy savings of 124 percent compared to just normal sleep. The reason for this is that during hibernation the energy consumption — per gram — is constant at any bodily size, meaning that a tiny animal weighing just a few grams has the same metabolism as a hibernating bear thousands of times its size, and so a gram of tissue from a tiny organism consumes as much energy as a gram of tissue from a giant one when in this state. With a small animal, they use far more energy in their active state than larger ones, so hibernation makes more sense for them compared to something more our size.
The basic gist is that when you scale it up, the larger the animal, the less effective and energy efficient hibernation is, and this is probably the main reason why most animals that hibernate are small. That is bad news for us, who have more in common with a bear than, say, a 25-gram leaf-eared bat. While small mammals like the brown bat or the pygmy possum can reduce their normal operating energy levels by up to 98 percent during hibernation, the same kind of energy savings simply would not be possible in humans, and the benefits of hibernation compared to just regular sleep would be negligible. Whereas small mammals can easily get by on their body’s stored energy reserves in fat and lean mass during hibernation, it seems that humans would not necessarily be able to do the same even if we could somehow induce hibernation in our species. Also there is the problem that even if we could work out the potentially dangerous and unstable process of super cooling our bodies to achieve hibernation, according to the study, you would need 6.3 grams of fat each day to hibernate in space, adding up to 450 pounds for a 90-year journey, meaning if an astronaut wanted to survive for decades through interstellar space to the nearest star, he/she would have to gain several hundred kilograms of fat before the flight. All of this means that it may be impossible for humans to pull off, and that the process may be just as out of our grasp as faster than light travel.
Nevertheless, this has not stopped researchers from trying to crack it. One of these projects is being conducted by SpaceWorks Enterprises, Inc., an aerospace design contractor for NASA and the Department of Defense. They are working on a detailed plan for a torpor-enabled mission to Mars, including detailed plans for the habitat and landing craft of a 6 to 8-person crew, who would make the trip in hibernation. They designed a crew habitat with closed-loop oxygen and water production systems for torpor that would keep at least a few astronauts awake on a rotating basis for piloting and interventions, after which they designed three interconnected habitat modules for a 100-passenger “settlement class” Mars mission, featuring two compact, rotating habitat modules to stimulate gravity, each one of these accommodating 48 passengers in torpor, with a separate habitat module to accommodate four care-taking astronauts on duty throughout the mission in rotating shifts to keep an eye on things. It is envisioned that the ones in hibernation would receive artificial gravity to minimize muscle loss and bone degradation, as well as regular electric stimuli to keep muscle mass and they would receive all nutrients—electrolytes, dextrose, lipids, vitamins, etc.— via liquid through a catheter inserted in the chest or the thigh, with enough of these nutrients stocked for 180 to 500 days per person depending on the needs of the mission, and radiation shielding would protect them. The SpaceWorks team initially proposed a two- to three-week hibernation test with a small number of healthy pigs to examine the effects of torpor on a non-hibernating animal, but agency regulations prevented NASA from funding the study. Indeed, arranging for animal tests of the technology has proven to be difficult on ethical grounds, and Arthur Caplan, director of the division of medical ethics at New York University Langone Medical Center, has said of it:
I think NASA is right: Slow is the way to go. Pigs are somewhat physiologically similar to humans, so pigs are a reasonable animal model for testing. Though it’s fair to say to critics: The number of pigs involved in this kind of study wouldn’t amount to one’s week’s breakfast for the average American.
Nevertheless, the project has been pursuing study into hibernating animals such as Arctic ground squirrels, which hibernate for two thirds of the year with minimal muscle loss and side effects, for clues into the biochemical processes that allow this and how to apply it to humans. However, humans testing it on will likely prove to be just as hard to get approved as it is for animals. Caplan has said of this roadblock:
These people take risks every day; they understand the physiological risks because they test jets and know many colleagues who have died. I’ve had astronauts tell me they’ll enroll in any experiment just to get into space. Our job is to rein them in. We’ve had lots of healthy people who have volunteered for long-term torpor experiments. There’s a pent-up demand for people who want to punch out of life for six months. I’m sure the FDA wouldn’t approve of that. Even research on simple primates starts getting people up in arms.
With a lack of any real funding in the area and a poor understanding of how to make hibernation possible in humans or even how other mammals manage to pull it off at all, it does not look like an area that is making much progress. Indeed, although it sounds on the surface more feasible than coming up with some sort of warp drive, wormhole technology, or some other kind of way around the light speed barrier, we are no closer to sleeping our way to the stars than we are to faster-than-light-travel. Will this ever truly break out of the realm of science fiction and pure speculation? Will we ever find a way to feasibly reach beyond our solar system across the sea of stars, or will we forever remain confined to this rock? It remains unknown, but if we never do manage to launch out into the stars, it will not be for lack of trying.