Debate: [Science] Extraterrestrial life

[Eddy]

Here we go

Do you believe in the existence of aliens?
Explain your answer!

My answer:
Despite the fact that I have no concrete proofs to sustain my theory aside from the researches NASA made throughout the history, I really do believe that aliens exist due to various reasons.
Let's talk about our planet first, the earth.
What made life possible in our planet? Since I was a kid I kept hearing from teachers on how the earth is like "made" perfectly to contain life.
The solar system... the position of the earth on it... the layers surrounding our planet... the availability of water
..., all of those permitted, through evolution the existence of complex life forms.
So, in other words, unless there isn't a planet with the same characteristics of the earth life is not possible? or it's just about the complex life forms?
What I know is that the key to life is always the water, that's why researchers are trying so desperately to find it on the various planets explored.
About complex beings I honestly don't know, but... if there is another kind of "life"? I mean, an organism which works differently somewhere in our vast space?
In any case, NASA already discovered many planets which could host extraterrestrial life using the spacecraft Kepler.
Here is the definition of Habitable Zone: Habitable Zone
And here a link about Kepler's discoveries: Kepler
I don't really know if someday they will be able to really proof something concrete but I'm really confident on the fact that there are other life forms in the space!