Could we sleep all the way to Mars? Future astronauts might be too big

'Humans are simply too large, so the benefits of hibernation are little'.
Derya Ozdemir
The photo credit line may appear like thisEvgeniyShkolenko/iStock

If astronauts are going to take on space crusades that'll potentially last beyond their lifetimes, they'll probably need to take the Hollywood sci-fi movie route to be capable of artificially inducing hibernation to survive the trip.

This would mean drastically reducing the body’s metabolic activities and needs to make sure the astronauts will make it to the other side. And that's a concept we are familiar with -- astronauts eerily asleep in a frosty tube-shaped pod as their spaceship glides through time and space. However, is this sci-fi trope really possible in real life?

A new study published in the journal Proceedings of the Royal Society by a group of researchers from Chile has now revealed a mathematical hurdle to turning the potential of human hibernation into reality. And if their research holds true, that might mean it's forever beyond our reach, metabolically speaking.  

What happens during hibernation?

Hibernation is a method through which animals store energy in order to withstand harsh weather conditions or a shortage of food. It is characterized by physiological changes such as a decrease in body temperature and a slowing of metabolism. Hibernation is not just a long period of sleep, as many animals periodically do wake up during this process. 

When smaller animals like ground squirrels and bats hibernate, body temperature drops and metabolism slows down, as well as heart rate and respiration dropping. In extreme situations, this method can minimize energy expenditure by up to 98 percent.

The recent study investigated how much energy different mammals save during hibernation and the possibility of human hibernation, and reached two conclusions about how hibernating animals save energy.

The researchers uncovered a bare minimum of metabolism that permits cells to survive in freezing, low-oxygen environments, and saw that most larger bears, for example, are not saving energy during hibernation, but losing it. This is because, during hibernation, the energy consumption per gram remains constant regardless of body size, causing a hibernating bat to have the same metabolism as a 20,000-fold larger hibernating bear. 

What happens if humans hibernate?

This would imply that artificially induced hibernation in humans for long-term space travel saves no more energy than regular sleep.

Applying the same principles to a hibernating adult human would mean that you'd need 6.3 grams of fat each day to hibernate in space. Over the course of a year, this would amount to about two kilos of weight.

While these figures may make sense for shorter travels, the average adult wandering through interstellar space to a neighboring star would need to gain a few hundred kilos of fat or wake up every day to refuel their engines with high-fat meals. 

"Humans are simply too large, so the benefits of hibernation are little as in bears if we think just on energy savings," Roberto Nespolo, the lead author of the study and a researcher at the Universidad Austral de Chile, told Newsweek

And the elephant in the room, of course, is how to get humans to hibernate in the first place. While a team of researchers from the University of Tsukuba was able to identify neurons in the brains of rodents that can be artificially stimulated to induce a state similar to hibernation, humans cannot hibernate, and potential research on hibernation in humans is fraught with ethical quandaries. And based on the results of this study, going through all the danger and effort of cooling our bodies, lowering our heart rate and breathing, and artificially slowing our metabolism may not provide the desired benefits.

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