Famed astrophysicist Neil deGrasse Tyson held an “Ask Me Anything” session on Reddit on Sunday, telling readers that he’s ready for all questions as long as they’re limited “to life, the universe, and everything.”

As the focus turned to space exploration, somone asked Tyson if he’d consider a trip to Mars. Tyson replied that since he really likes Earth, it’d have to be a round-trip ticket. Then he tacked on another condition for the boss of SpaceX and Tesla TSLA, +0.14%

‘I’m not taking that trip until Elon Musk sends his mother and brings her back alive. Then I’m good for it.’ Neil deGrasse Tyson

Still, Tyson went on to explain how important SpaceX’s recent strides are for the future of realistic space travel. “Any demonstration of rocket reusability is a good thing,” he said. “When we fly on a Boeing 747 across great distances, we don’t throw it away and roll out a new one. Reusability is arguably the most fundamental feature of affordable expensive things.”

While he says he’s one of SpaceX’s biggest supporters, he also admitted to being one of the company’s biggest critics.

“Projects that are hugely expensive and dangerous, with uncertain returns on investments, make poor activities of profit-driven companies,” Tyson explained.

“Governments do these things first, allowing private enterprise to learn what to do and what not to do, then come next with a plan that involves us all,” he added. “So my read of history is that private companies will not be the first to send humans to Mars unless government actually pays for it.”

Other highlights from the Reddit interview session include Tyson’s favorite fiction book (“Gulliver’s Travels”), his favorite comedians (Richard Pryor and Eddie Murphy, among others), and his thoughts on whether we’ll make contact with complex organisms from other planets within 50 years (no).

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