NASA Study Confirms Astronaut Scott Kelly's DNA Was Altered in Space Preliminary findings from a study performed by the space program examined Kelly's DNA compared to his twin brother, Mark Kelly's, who is also an astronaut. They looked at the brothers' DNA before and after Scott's year long trip to the International Space Station, and determined that while 93 percent of his genes went back to normal, seven percent remained altered. NASA The study, in addition to Scott's extended stay in space, are viewed by NASA as "stepping-stone[s] to a three-year mission to Mars."