Faith is a measure of irrationality

[GrandizerII]

Certainly we do not know for sure if life exists elsewhere in the universe, but considering all the atoms that came from the big bang are everywhere it should not shock us at all. Not to mention like you said, the sheer size would make it a likelihood.

May I call that faith? Can faith be defined as “believing what is likely, but not confirmed” or am I taking too much liberty?

Yeah, you're free to call that faith, so long as you understand the key distinction between this sort of faith and the faith that Christians and other religious often defend and justify.

By the way, I think it's pretty much been confirmed in many ways and yet to be falsified. Which is why we say it is likely as well. I don't think we could ever say, for most cases at least, that something's been absolutely 100% confirmed to be true.