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I haven't a clue if there is life on other planets but I'd be charmed if we found a unicellular organism on Mars. It would change our whole concept of life on Earth.

Intelligent life on a planet comes of age when it first works out the reason for its own existence.

The universe is large and old, and the ingredients for life as we know it are everywhere, so there's no reason to think that Earth would be unique in that regard. Whether of not the life became intelligent is a different question, and we'll see if we find that.

I believe alien life is quite common in the universe, although intelligent life is less so. Some say it has yet to appear on planet Earth.

What we expect to find, certainly in our own solar system, are probably simple single or multiple-cell forms of life. To get to intelligent life takes stability of conditions over huge, long periods of time.

The discovery and investigation of life on other planets is likely to change many of our ideas about how life arose on the Earth and even what is life and its natural development.

This planet seems to be in such sorry shape. And I can't ever think about the rest of the universe without coming back home and thinking what the implications for life here would be if we were to really have some definitive proof of extraterrestrial life.

When I was a little kid, we only knew about our nine planets. Since then, we've downgraded Pluto but have discovered that other solar systems and stars are common. So life is probably quite prevalent.

I think it'd be pretty unrealistic to think we're the only planet in the world with thinking beings. It's kind of a strange conceit. Especially given how many universes there must be.