NASA’s Chief on the Odds Aliens Have Already Found Earth

You've said before that the odds that aliens exist is pretty high. NASA's actively looking for them. That's part of what NASA does, of course.What exactly are you looking for. A lot of what we're doing is just looking for, you know, what are the building blocks to life and biosignatures that are out there. Better than 90% chance you bring the samples home from Mars.You will prove that there was once microbial life on on Mars. And I think most people look up in the night sky and say, surely it's out there so ...