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I believe that there may be intelligent life on other planets.

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.

If this is the only planet on which not only life, but intelligent life, has arisen, that would be very unusual.

There may be aliens in our Milky Way galaxy, and there are billions of other galaxies. The probability is almost certain that there is life somewhere in space.

The vast majority of terrestrial species are in fact microbes, and scientists have only begun scratching the surface of the microbial realm. It is entirely possible that examples of life as we don't know it have so far been overlooked.

Should we find a second form of life right here on our doorstep, we could be confident that life is a truly cosmic phenomenon. If so, there may well be sentient beings somewhere in the galaxy wondering, as do we, if they are not alone in the universe.

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.

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.

Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us.

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.