No need to be from another galaxy. Suppose that Mars had very fast spaceships one billion year ago. A Martian starts a journey at near light speed, even just or

No need to be from another galaxy. Suppose that Mars had very fast spaceships one billion year ago. A Martian starts a journey at near light speed, even just orbits around the solar system. Comes back 2k years ago and finds a red desert. Visits Earth, finds it underdeveloped, does a short journey, comes back to Earth now and starts making friends.