Stephen Hawking, the eminent theoretical physicist, made headlines earlier this year by advising against any attempt to contact aliens. Now, he has suggested our survival as a species depends on colonizing other planets. (Listen to Hawking's claims.) A guide to Hawking's latest grim prophecy:

Why does humanity's future lie in outer space?
Because "great dangers" face the human race over the next two centuries, Hawking told delegates at a Big Think conference. With finite resources on earth and humankind's "aggressive" genetic instincts, our "only chance of longterm survival" may be to "spread out into space."

Is Hawking the first to deliver such a message?
Not at all. Rocket science pioneer Konstantin Tsiolkovsky warned as long ago as 1895 that while "earth is the cradle of humankind... one cannot live in the cradle forever." Carl Sagan and Arthur C. Clarke also both made similar predictions.

Where would we go?
"Mars would offer the best nearby second home for humanity and our allied species," says Alan Boyle at MSNBC. In the long term (that is, in the next few billion years) humankind will have to escape the inner sector of our solar system before the sun begin expanding dramatically in its final stages of life.

How should we go about escaping planet Earth?
Hawking says the first step — the one we should be concerned with at the moment — is much greater investment in manned space flight.

Isn't Hawking being a bit too gloomy?
He certainly is, say the editors at the Calgary Herald. Hawking's "glass-half-empty view of humankind" is "defeatist." It's insulting to argue we don't have the ability to save ourselves. Not so, says Andrew Moseman at Discover magazine. Hawking is "pushing urgency and vigilance, not gloominess... He's just the kind of person who thinks on the long, long term."

Sources: Discover, Huff Po., MSNBC, Calgary Herald