Long-term space travel poses severe health risks, including radiation exposure, muscle and bone loss, and psychological strain. Scientists are exploring hibernation, a 250-million-year-old physiological strategy, to mitigate these hazards. By inducing a state of synthetic torpor, they aim to protect astronauts on missions to Mars and beyond, while also developing treatments for diseases on Earth.
Hibernation's protective mechanisms
Hibernation allows animals to survive months without food or water by drastically reducing metabolism. During hibernation, animals pack DNA tightly, reduce oxygen use, and activate potent DNA repair mechanisms, shielding them from radiation. For instance, the 13-lined ground squirrel drops its heart rate to one beat every several minutes and body temperature to 4°C. Elena Gracheva, a physiologist at Yale University, studies how these squirrels survive without water for up to eight months, identifying a brain region (subfornical organ) and a molecule that abolishes thirst when injected.
Inducing synthetic torpor in humans
Researchers are developing noninvasive techniques to induce synthetic torpor in humans. Kelly Drew, a biochemist at the University of Alaska, studies arctic ground squirrels that hibernate from August to May, dropping body temperature below freezing. Her team found that myosin, a muscle protein, changes energy use during hibernation to survive cold. Since 2023, groups have used ultrasound to trigger torpor in animals, avoiding invasive brain surgery. Matteo Cerri, a University of Bologna physiologist, plans to test ultrasound on healthy human volunteers soon.
Brain circuits and metabolic control
MIT researcher Siniša Hrvatin identified the preoptic area of the brain as a key regulator of torpor. By activating neurons in hamsters, he induced torpor with body temperatures dropping to 15°C. This circuit likely exists in many animals, including non-hibernators, suggesting humans could be induced into a similar state. Clifton Callaway at the University of Pittsburgh gave healthy humans the sedative dexmedetomidine for five days, reducing metabolic rate by 20% and calorie consumption by 30%. He notes that a trip to Mars requires about 300 kg of food per astronaut; reducing that by a quarter would significantly cut payload.
Medical applications on Earth
Synthetic torpor holds promise for treating cancer, Alzheimer's, Parkinson's, heart failure, and asthma. Hibernation triggers repair and regeneration across organs and hinders cancer cell growth. Researchers at the University of Groningen isolated the molecule SUL-138 from Syrian hamsters, which has protective properties in non-hibernating animals. They have begun a small human trial for Parkinson's. Callaway, an emergency room doctor, suggests torpor could improve upon therapeutic hypothermia for heart attacks and strokes by avoiding shivering and inflammation.
Challenges and timeline
Christiane Hahn of the European Space Agency notes that inducing torpor is well understood, but safely awakening individuals remains a challenge. She estimates it will take several decades before synthetic torpor is used in spaceflight. Cerri is more optimistic, predicting human use within 10 to 15 years. Hrvatin sees organ transplantation as a likely early application, as activating hibernation pathways can extend organ longevity.
