It's not a surprise that Neil deGrasse Tyson's TV show 'StarTalk' has had its share of unexpected celebrity guests, including most recently, the former president Bill Clinton. However, the renowned astrophysicist recently admitted that there are two dream guests that he would like to talk to in his National Geographic Channel show: President Barack Obama and former 'Spin City' actor Charlie Sheen.

It's easy to explain why Neil deGrasse Tyson would want President Obama in 'StarTalk' but he did offer TVLine a lengthy explanation on why he is so keen in having Charlie Sheen on the show.

"Well, he once visited the museum with his ex-wife and their daughter... We chatted briefly and I said, 'Why don't you guys come up to my office, because I've got some crazy stuff to play with in my office? There's something for the kid, something for everybody,'" Tyson said, adding that things the former 'Two and a Half Men' star got inquisitive when they came up.

"He spent 20 minutes asking me deep questions about the universe on his own, unprompted," he continued, quoting one of Charlie Sheen's questions. "'Well before the Big Bang, what could've been made the Big Bang? Don't you need an energy source that could lead up to it that could make that happen?'"

Neil deGrasse Tyson was obviously impressed with the actor from the encounter. "Intelligent, thoughtful, deep questions as though he thinks about this while no one's looking or paying attention," he said of Charlie Sheen. "So I want him on the show, because that's the last thing you'd expect him to have a conversation about: the fate of the universe."

Although it is still unclear whether Charlie Sheen will be a guest on 'StarTalk' soon, the second season will feature appearances from Susan Sarandon, David Byrne and Seth MacFarlane, who worked with Neil deGrasse Tyson on the TV series 'Cosmos: A Spacetime Odyssey.'