Retired NASA astronauts and identical twins Scott and Mark Kelly might not be so identical anymore.
NASA confirmed preliminary findings from its Twins Study in which Scott Kelly spent almost a year in space while his twin brother stayed on Earth as a control. The space agency wanted to see how spending a long time in space affects the human body.
Seven percent of Scott Kelly's genes did not go back to normal after returning to Earth. That means the formerly identical twins are no longer genetically the same.
NASA says that 7 percent difference points to possible long-term changes in genes related to Scott Kelly's immune system, DNA repair, bone formation networks and more. The mutations are thought to be caused by the stresses of space travel.
NASA wants to use what it learned from the Twins Study to inform future long-term missions, like to Mars.
Additional reporting from Newsy affiliate CNN.
