A year on the space station has an undeniable impact across the human body, but many of the body’s systems recover after a return to Earth.
Human bodies did not evolve to float in microgravity or to thrive under the radiation levels in space. When NASA astronaut Scott Kelly spent nearly a year on the International Space Station, in a mission launching in 2015, his body was put under incredible stress: Fluids swelled his upper body and head, his genes activated in different ways, and his immune system jumped into overdrive compared to that of his identical twin, Mark Kelly. Mark has also flown in space, but he remained on the ground during that long-duration mission. Over time, Scott experienced decreased body mass, instability in his genome, swelling in major blood vessels, changes in eye shape, metabolism shifts, inflammation and alterations in his microbiome — as well as a strange lengthening of his telomeres, the protective structures at the ends of chromosomes. (They shortened again after he landed.)
Ten teams working on NASA’s Twins Study — encompassing 12 universities and 84 researchers — followed the duo before, during and after the flight, tracking the twins’ biology to see how the brothers changed over the course of the study. While the research was very limited in scope, scientists planning to send astronauts on long trips to the moon, Mars and beyond will find this data on long-duration spaceflight invaluable.