Astronaut Chris Hadfield is a reasonable man, a former commander of the International Space Station, and a social media superstar.

He recently went on WNYC's Brian Lehrer show to discuss his life and career when a caller asked him about the existence of "alien life."

"I don't know of any astronauts who think we're alone in the universe," Hadfield replied.

Now, he's obviously not talking about the UFO-Area-51 imaginary kind of aliens. He's commenting on the possibility that somewhere out there, on some other planet, there are the bags of chemicals we call organisms reproducing themselves.

And in that belief, he's in the mainstream of astrobiological thought, as Lane Wallace explained this week. There are just so many galaxies, which are filled with so many stars, which are circled by so many planets ... How could there not be life, even if we haven't found it?