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In a previous study, the European Space Agency (ESA) considered astronaut hibernation to be a possibility for long-duration missions. Induced hibernation, or “wintering” to use the exact term for the bear, which inspired the method, would notably reduce energy requirements. But is it really feasible? Chilean researchers argue that the savings made had not been calculated correctly until now. By comparing the energy savings and expenditures of different mammals during hibernation, they suggest that — from a metabolic perspective — humans are unlikely to survive a decades-long journey through space.
Put in a state of torpor (hibernation) or hibernation, the body would see its metabolism decrease in order to achieve savings in oxygen, food and water needs. During a long flight, this could thus present a considerable advantage; especially since such a trip requires ” about 30 kg per astronaut per day, and we have to take into account the radiation as well as the mental and physiological challenges “, explained last January in a press release Jennifer Ngo-Anh, coordinator of research and payload of human and robotic exploration at ESA.
While hibernation is a natural state experienced by many mammals and has been interpreted as an adaptive energy-saving strategy, Chilean researchers have looked in detail at the relationship between body mass and energy expenditure in mammals. hibernating animals. According to them, the calculation is useful in determining ” the lifespan of hypothetical astronauts in space, or the size limit at which hibernation becomes ineffective “.
Only small mammals save energy during hibernation
The results of the study are surprising: on average, small mammals that hibernate tend to save much more energy than large animals. For example, the tiny 45-gram marsupial saves 76% of its energy during hibernation, compared to its usual active state. The brown bat and the pygmy opossum can even reduce their normal energy levels by up to 98% during hibernation! If we keep in mind the bear as the main mammal that hibernates, it actually weighs only 70 grams on average.
In contrast, large bears do not save energy during hibernation, but on the contrary lose it. For example, a grizzly achieves a negative energy saving of 124%. Even a smaller bear (75 kg) does not realize any energy gain during hibernation, compared to a normal sleeping state.
It should be noted that in their normal state of activity or sleep, small animals must burn more energy than large ones to maintain their body temperature. But everything seems to equalize in a state of hibernation, regardless of body size. ” We estimated the daily energy expenditure scale of hibernation and found that it scales isometrically with mass write the researchers in their study. “Which means that one gram of bat in hibernation has a metabolism similar to that of one gram of bear, 20,000 times greater “.
This therefore becomes a more important advantage for small living beings, and of little interest for larger ones such as bears and humans. According to this study, artificially induced hibernation for the astronaut in humans would therefore probably not save more energy than normal sleep.
Thus, small mammals can easily reap the benefits of hibernation through stored energy reserves in muscle and fat, whereas humans would not be able to do the same. And even if we considered it, space travel could not exceed a few short years, because the loss of fat would be significant. According to the study, it would take 6.3g of fat per day to hibernate in space, which is about 204kg for a 90-year journey.