 Kelly 's identical twin brother , Scott Kelly , is also an astronaut . The Kelly brothers are the only siblings to have both traveled in space . In 2015 , Scott Kelly began a mission spending a year in space on the International Space Station . He returned to Earth on March 1 , 2016 after 340 days in space . During and after Scott 's year @-@ long mission , the brothers will be studied to find differences between living on Earth and in space . 
