Is there anybody out there? Well, one space expert says there could be lots of planets like Earth where things could live.
So far, telescopes have found just over 300 planets outside our Solar System.
But Dr Alan Boss from the Carnegie Institution of Science says there could be one hundred billion planets like Earth in our galaxy.
Dr Boss told a science conference in America that many of them might even have simple life forms living on them.
Experts say that very few of the planets they've found so far would be capable of supporting life.
Dr Boss says we could discover Earth-like planets in the next few years!
Most of them are so close to stars they would be too hot for anything to survive on them.
But Dr Boss estimates that each Sun-like star probably has a planet like Earth which is capable of supporting life.
That doesn't mean there are little green men, or even humans or animals living out there, but Dr Boss thinks there could be tiny bugs or bacteria.
He said: "I think that most likely the nearby 'Earths' are going to be inhabited with things which are perhaps more common to what Earth was like three or four billion years ago."
It might not be too long before we find out if Dr Boss is right.
He said Nasa's Kepler mission, which is due to be launched in March, should begin finding some of the Earth-like planets within the next few years.