Here’s why hibernation in space might not be possible for humans after all

Sending humans virtually anywhere in space beyond the Moon pushes the logistics of health, food, and psychology to limits we are only beginning to grasp.

A basic solution to these problems in science fiction is to simply put Void Travelers to bed for a while. In a state of sleep close to hibernation or torpor, the metabolism drops and the mind is spared the boredom of waiting for endless empty hours.

Unlike faster-than-light travel and wormholes, the principle of putting astronauts into a form of hibernation seems to be within reach. Enough for even the European Space Agency to take a serious look at the science behind it.

Implications of a new study by a trio of Chilean researchers now reveal a mathematical obstacle to turning the potential for long-term human stasis into reality, one that could mean it is forever out of our reach.

Roberto F. Nespolo and Carlos Mejias of the Millennium Institute for Integrative Biology and Francisco Bozinovic of the Pontifical Catholic University of Chile set out to unravel the relationship between body mass and energy expenditure in hibernating animals.

They discovered a minimum level of metabolism that allows cells to persist in cold, oxygen-poor conditions. For relatively heavy animals like us, the energy savings we might expect from entering a state of deep hibernation would be negligible.

In fact, we’d probably be better off just taking an old-fashioned nap.

The word hibernation often conjures up images of a bear nestling in a den for a long winter’s rest.

While bears go out for several long, cold months, their dormancy isn’t quite like true hibernation in small creatures like ground squirrels and bats.

In these animals, body temperature drops, metabolism decreases, and heart rate and respiration slow. This process can reduce energy expenditure by up to 98% in some cases, eliminating the need to waste effort hunting or foraging.

However, even in this state, the animal can still lose more than a quarter of its body weight by burning off its fuel reserves.

If we applied the same basic math to a hibernating adult human, a daily food intake of around 12,000 kilojoules would be replaced by a need for only a few hundred kilojoules of body fat.

Keeping this scenario, we could imagine that our intrepid space tourist snuggled up in his specially equipped bed would lose just over six grams of fat a day. Over a year, that would be about two kilograms of weight.

That might be fine for a quick trip to the Jovian moons, but if the average adult wants to survive decades floating through interstellar space to a nearby star, they’ll need to pack a few hundred extra pounds of fat. That, or waking up regularly to throw in a lard shake or three.

These rough calculations are based on many assumptions, not the least of which is hibernation scaling. After all, there’s probably a good reason behind the rarity of huge hibernating mammals our size (or larger).

The researchers therefore carried out a statistical analysis on a variety of hibernating species, as detailed in previous studies.

From this, they concluded that the daily energy expenditure of hibernating animals ranges fairly evenly, such that one gram of tissue from a tiny mammal, such as the 25-gram leaf-eared bat , consumes as much energy as one gram of tissue from an 820 gram hibernating ground squirrel.

We might assume that if we ever figured out how to hibernate as efficiently as a dormouse, every gram of our tissues would require the same energy as every gram of theirs.

It’s a different story when mammals are active, however. Scaling the relationship between active metabolism and mass yields a slightly different graph that reveals a point at which hibernation doesn’t really save much energy for larger beasts.

This point is close to our own mass, which implies that our total energy needs during hibernation will not be significantly different from those while we are simply at rest.

This might explain why bears don’t really hibernate the way small animals do. And that also means for us humans, taking all the risks and going to the trouble of cooling our bodies, lowering our heart rate and breathing, and artificially depressing our metabolism might not give us the results we were hoping for.

If we want to save our boredom and avoid munching on the ship’s supply of freeze-dried ice cream, we might as well stuff ourselves The extentgrab a bunch of sedatives and doze off towards Mars.

Forcing humans to hibernate just won’t be worth it.

This research was published in Proceedings of the Royal Society B.