DOUNIAMAG-US-SPACE-TWIN BROTHERS-SCIENCE-NASA

Recent photo released by NASA shows former astronaut Scott Kelly (R), who was the Expedition 45/46 commander during his one-year mission aboard the International Space Station, along with his twin brother, former astronaut Mark Kelly (L). The Twins Study, by the Journal Science, is helping scientists better understand the impacts of spaceflight on the human body through the study of identical twins. Retired astronaut Scott Kelly spent 340 days in low-Earth orbit aboard the International Space Station while retired astronaut Mark Kelly, his identical twin, remained on Earth. The twins' genetic similarity provided scientists with a reduced number of variables and an ideal control group, both important to scientific investigation. (Photo by Robert MARKOWITZ / NASA / AFP) (Photo by ROBERT MARKOWITZ/NASA/AFP via Getty Images)