Scientists are getting new insights into how human hibernation could be possible during space travel from an unlikely source: by studying the blood of bats.
Biophysicists and biochemists at Greifswald University in Greifswald, Germany, report that through careful comparative analysis of bat and human blood samples, they discovered encouraging evidence that humans may be capable of safe medically induced hibernation during space travel. The research was recently published in the Proceedings of the National Academy of Sciences.
Human Hibernation in Space
In nature, many species hibernate to avoid natural conditions such as low temperatures and the food scarcity accompanying such weather. Entering a hibernation state minimizes energy use and preserves the creature until environmental conditions and food supplies can improve.
It’s more complex than just going to sleep, though. Hibernation states must manage potential stressors on the body, like long-term waste buildup and low-temperature blood circulation. While many animals enter the state to combat the unavoidable changes occurring in their environment, humans may need to explore hibernation as a potential pathway to alien environments, such as those encountered during space travel.
Long a feature of science fiction, human stasis could be the key to achieving the years-long space flights required of future astronauts. Even reaching Earth’s neighbor Mars would be a nine-month trip, while Saturn’s intriguing moon, Titan, is at least a two-year, one-way journey.
Considering such challenges, the Griefswald team’s recent progress toward inducing an artificial hibernation state in humans offers a glimpse into the potential future of space travel.
Bat Blood and Humans
The Greifswald team undertook a comprehensive four-quadrant approach to examine the blood of three species and postulate what a fourth type, a hypothetical hibernating human blood, should be like. Specifically, they studied the hibernating typical noctule bat (Nyctalus noctula ), the nonhibernating Egyptian fruit bat (Rousettus aegyptiacus), and modern humans (Homo sapiens ).
Their method involved comparing the blood of a hibernating bat species to that of a non-hibernating bat species to determine the characteristics that make blood more suitable for the task. They then compared the bat blood to that of humans, identifying differences between human and bat blood and what specific pro-hibernation characteristics were missing.
The primary focus area within the blood was red blood cells (RBCs), which comprise most human or bat blood components. RBCs are almost 45% of blood volume and significantly impact blood flow. Drilling down even further, RBCs’ ability to alter their shape substantially impacts blood flow by changing the viscosity and allowing blood to flow into tiny capillaries, potentially with an even smaller diameter than an RBC itself.
Despite recognizing how vital blood flow is to survival and the many RBC variables that come into play, there is a lack of existing research on cellular-level blood flow mechanics at low temperatures in nonhuman animals, like a creature would experience during hibernation now.
In Cold Blood
The team chilled blood samples to 37°, 23°, and 10° Celsius to observe the blood under the various conditions likely for animal bodies in cold weather. 37° C mirrors the active daytime core temperature of bats or humans, while 23° C is about as cold as human extremities can reach, and 10° C represents the depth of chill bats can enter during hibernation.
The Griefswald team utilized dynamic real-time deformability cytometry to investigate the samples’ viscosity and cell stiffness at various temperatures. The researchers found that both bat species had much smaller RBCs than humans. However, human RBCs could potentially achieve a similar low-temperature elasticity and viscosity to those of hibernating bats. This is a crucial discovery, as it hints at the possibility of humans safely entering a medically induced hibernation state.
There is one significant difference, though. Human RBCs recover from low-temperature states much more slowly than bats. While this could be a problem, other large mammals, such as bears, hibernate at higher temperatures (around 20° C), which could minimize some of our species’ difficulty with handling very low temperatures compared to bats.
Working Toward Space Hibernation
The benefits of hibernation are clear. Scientists estimate that even a tiny drop of 1 C core body temperature can save 6% of metabolic energy. Humans could not only eliminate some of the long-term psychological effects of their journey but also require far less sustenance.
The team’s next question is whether pushing humans’ viscoelastic response closer to that of bats is possible. Antioxidants have been identified as a potential starting point for the search, and only through further investigation can scientists determine if humans can safely enter a hibernation state, one that could help open new pathways to the cosmos by enabling long-distance space travel.
The paper “Thermomechanical Properties of Bat and Human Red Blood Cells—Implications for Hibernation” appeared on October 14, 2024, in the Proceedings of the National Academy of Sciences.
Ryan Whalen covers science and technology for The Debrief. He holds a BA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.