From March 2015 to March 2016, Astronaut Scott Kelly spent 340 days at the International Space Station, while his twin brother, Mark Kelly, remained grounded on Earth. After years of collecting and processing data from the Kelly brothers, the official study was finally published in the journal Science.
Researchers found that the year in space modified Scott Kelly's physiology, but many of these changes vanished after time back on Earth. During his time in outer space, Scott lost weight, while his brother gained weight. He also peed less frequently and exhibited signs of dehydration. And although his immune system shifted significantly while he was in outer space, the flu vaccine still worked effectively, showing that it was still capable of functioning correctly.
But there were, however, certain exceptions. For one, his gene activity behaved differently in space. His cells turned certain genes on and off in different ways than they did when grounded on Earth. When he reached the space station, approximately 1,400 of Scott's genes changed their behavior, possibly as a result of changing bodily demands. And in the latter half of the trip, genes related to immune responses and DNA damage particularly changed, and approximately nine percent of his genes that had altered during his trip didn't go back to typical functioning.
Colorado State University-Fort Collins radiation cancer biology professor Susan Bailey examined Scott Kelly's DNA Even closer. They wanted to see what the effect of a year in outer space would be on the ends of his chromosomes, called telomeres. They usually get shorter as we age and accumulate stress, and shortened telomeres share a correlation with age-related diseases like heart disease. So experts expected his telomeres to shrink in outer space, given the extremely stressful process of space flight, but instead, they lengthened.
“It’s exactly the opposite of what we thought, it was in every sample, every time point,” Bailey said. Even stranger, his telomeres shrank when he landed, and nine months later, there were significantly more missing or even shorter telomeres than previously.