This is an interesting question, but let's define terms:

1. Life on another planet at something approximately as complex as the cellular level (Earth equivalent: from viruses to dogs)
2. Life on another planet that we would recognize and characterize in broad terms as "intelligent" (Earth equivalent: great apes, dolphins, elephants, humans, etc)
3. Intelligent life from another planet that has visited this planet

I say yes to (1), which I believe will prove to be quite common.

I say yes to (2), but I believe almost all such species go extinct almost immediately (relative to geological time scales0

I say no to (3), because of my answer to (2).

hi Paul, thank you for your explanation.but still there is something out there. So what was that ? that i have seen their aeroplane. It was so clear to me they are exist . oops sorry :(

Okay Michiyo - I am always interested in a story from someone who saw extraterrestrials. Tell us what happened?

I certainly think it's possible, even likely, that extraterrestrials exist. The universe is so vast, there is much we don't know.

Konnichiwa

Geek humor on this subject:

http://xkcd.com/384/

as in, UFO's abducting cows and people and making crop circles? nope

"Believe" is a strong word. I'm 99% certain there is intelligent life in the universe, but I'd give it about 5% likelihood they've visited Earth.

Sure. But do I believe that they are visiting, have visited, or will visit soon, not so much.

I do. I have my own SETI station up and running right now. .