Hibernation is a way for many creatures – from butterflies to bats – to survive cold, dark winters without having to forage for food or migrate to somewhere warmer. Instead, they turn down their metabolisms to save energy.
Sending humans virtually anywhere in space beyond the Moon pushes logistics of health, food, and psychology to limits we’re only just beginning to grasp.
A staple solution to these problems in science fiction is to simply put the void-travelers to bed for a while. In a sleep-like state akin to hibernation or torpor, metabolism drops, and the mind is spared the boredom of waiting out endless empty hours.
Implications of a new study by a trio of researchers from Chile now reveal a mathematical hurdle to turning the potential of long-term human stasis into reality, one that might mean it’s as forever beyond our reach.
Roberto F. Nespolo and Carlos Mejias from the Millennium Institute for Integrative Biology and Francisco Bozinovic from the Pontifical Catholic University of Chile set out to unravel the relationship between body mass and energy expenditure in animals that hibernate.
They discovered a minimum level of metabolism that allows cells to persist under cold, low-oxygen conditions. For relatively heavy animals like us, the energy savings we might expect from entering a deep, hibernation-like state would be negligible.
In fact, we’d probably be better off just napping our days away the old-fashioned way.
The word hibernation often invokes images of a bear tucked away in a den for a long winter’s rest.
In these animals, body temperature plummets, metabolism shrinks, and heart rate and breathing slow. This process can reduce energy expenditure by as much as 98 percent in some cases, removing 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 as it burns through its fuel reserves.
If we applied the same basic mathematics to a hibernating adult human, a daily food intake of around 12,000 kilojoules would be replaced by a need for just a couple hundred kilojoules of body fat.
Keeping with this scenario, we might imagine our intrepid space tourist tucked up in their specially-kitted bed would lose just over six grams of fat a day. Over a year, this would add up to around two kilograms of weight.
This might be fine for a rapid journey to the Jovian moons, but if the average adult wants to survive decades floating through interstellar space to a nearby star, they’d need to pack on an additional few hundred kilograms of fat. That, or routinely wake to throw back a lard milkshake or three.
So the researchers carried out a statistical analysis across a variety of hibernating species, as detailed in previous studies.
From this, they concluded the daily energy expenditure of hibernating animals scales in a fairly balanced way, so a gram of tissue from a tiny mammal, like the 25-gram leaf-eared bat, consumes as much energy as a gram of tissue from an 820-gram hibernating ground squirrel.
We could assume that if we ever worked out how to hibernate as efficiently as a dormouse, every gram of our tissue would require the same energy as every gram of theirs.
It’s a different story when mammals are active, however. The scaling of the relationship between active metabolism and mass produces a slightly different graph that reveals a point at which hibernating doesn’t really save a great deal of energy for bigger beasts.
That point is near our own mass, implying our total energy needs while hibernating aren’t going to be significantly different from those while we’re merely at rest.
If we want to save our boredom and keep from munching through the ship’s supply of freeze-dried ice cream, we might as well binge The Expanse, take a bunch of sedatives, and doze our way to Mars.
Forcing humans to hibernate just isn’t going to be worth the hassle.
Source: sciencealert
