It's been more than a year now since astronaut Sco...  ...s been more than a year now since astronaut Scott Kelly returned to earth after spending a year on the In...  ...and his identical twin brother, retired astronaut Mark Kelly , are the subject of a unique twin study comparing...  ...mparing the changes in...

Mark and Scott Kelly are identical twins who were both selected for NA...  ...are the only siblings ever to both fly in space. Mark Kelly flew the space shuttle for ten years, then retire...  ...retired in order to take care of his wife. Scott Kell...