He knows there are other planets -- the existence of other planets has been known for centuries, after all -- but they've only just been able to get planes in the sky. The idea of being able to visit other planets is so far on the horizon that it's not even visible yet.

"Middle of space." It's unbelievable, but then again, so was the existence of Amazons, and gods, and he's seen proof of those first-hand. So it's not stretching too far to accept that this may be true too. "Okay. So we're in the middle of space. After I believe that, what then?"