Astronaut Scott Kelly launched into space on a one-year mission to the International Space Station (ISS) in 2015. He was weightless for 340 days. His identical twin brother, retired astronaut Mark Kelly, stayed on Earth. Because they are identical twins, Scott and Mark Kelly share almost all the same genetic material, or DNA. They agreed to let scientists study them before, during, and after Scott’s mission to find out what a year floating in space may do to the human body. The investigation is known as the Twins Study ... and the first results are now in. In the Twins Study, researchers are looking at 10 aspects of the human body. They are doing the investigation for NASA’s Human Research Program. NASA is the American space agency. They introduced some early findings at a conference in Texas last month. At the conference, researchers said that some genetic changes occurred in Scott Kelly while he was in space. John Charles is the chief scientist for NASA’s Human Research Program. He says researchers expected some of those changes. But there was a surprise: a change to Scott’s telomeres. Telomeres sit on the end of chromosomes. Chromosomes are the part of cells that hold DNA. Usually, as people age, their telomeres become shorter. But when he was in space, Scott Kelly’s telomeres did the opposite: They became longer. Charles says usually astronauts have shorter telomeres than other people. He thinks this may be because their intense training on Earth is stressful. So being in space, Charles says, may actually be less stressful.