People are obsessed with Mars. But … why? Two confessed super-fans, Andy Weir, author of “The Martian,” and Stephen Petranek, author of “How We’ll Live on Mars,” share thoughts on why being Mars-mad is a reasonable state of mind.

Humans are off to live on Mars. At least, that’s the case journalist Stephen Petranek makes in his TED Book, “How We’ll Live on Mars.” According to Petranek, the move is no less than an “essential back-up plan for humanity.” Here, he shares just some of the factors those who make the first trip will have to manage.