Twin brothers Mark and Scott Kelly both served in NASA's astronaut corps. As twins, the Kelly brothers were ideal for a study on the effects of space travel. Beginning in 2015, Scott Kelly spent a year aboard the International Space Station while Mark stayed on terra firma. Whatever changes Scott Kelly's physiology underwent in space would be readily apparent by comparing him to his earthbound twin.
The results of that study were published this month in the journal Science, National Geographic magazine reports. While the study's authors cautioned against drawing too many conclusions based on the results, especially given the small sample size of just two people, scientists did find that Scott Kelly's chromosomes and DNA suffered damage, while Mark Kelly's did not. There were also changes to Scott Kelly's retina and carotid artery.
Pleasantdale Elementary School, where the two attended, was renamed in their honor in 2016.
Mark Kelly earlier this year kicked off his campaign for the U.S. Senate from Arizona. He is married to former Congresswoman Gabrielle Giffords.
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