Guy Fleegman: Hey! Don't open that! It's an alien planet! Is there air? You don't know!
Fred Kwan: [sniffs air] Seems okay.

"There are two ways to look at it. Given the vastness of the universe, it is highly probable that a close twin of Earth would exist somewhere; therefore, the mere existence of such a planet should not take us aback. On the other hand, the odds of such a twin turning up only a few thousand parsecs from the original planet... that is frankly unbelievable."