This is my first thread, but I've been lurking for some time. Such a great place to shirk my work responsibilities.
My question regards life on other planets, and our search for them. I apologize if this is common sense to you guys, but I'm not educated in science/mathematics beyond high school.
From what I've seen in documentaries and websites, our search for life on other planets begins with searching for other planets that share characteristics with Earth. I assume this is because we know that Earth can sustain life, therefore, due to the immensity of space, it's just more efficient to search for life on planets like ours.
So we find some giant planet orbiting a distant star, but it's way too close to its star, so we assume there is no "life" because it's too hot.
But my question is whether life can definitely not exist on planets completely unlike Earth? (Sorry for the multiple negative.)
A friend of mine said "well, there might be life on other planets, but who knows what that life would be like? Perhaps life can exist on a planet with no atmosphere in forms that we are unfamiliar with. Or on a planet with a nitrogen atmosphere, with life adapted to that. Or perhaps some life-forms don't have to breathe at all?"
Is there some reason why life cannot exist on a planet as close to its star as Mercury? Or as far as Neptune? Or without oxygen?
Is it known with certainty that those environments cannot sustain life? (I guess I'm thinking of a chemical reason, like temperatures above X or below Y do not permit bonding beyond Helium, or something like that.)
Or do we just not know how it would be possible?
Thanks, and I'm sorry if this doesn't make much sense. I'll try to clarify if necessary.