As far as I know, scientists seeking extraterrestial life are simply looking for plantets containing water in liquid state. To be honest, I find this weird.
It is true that life - in the form we know on Earth - cannot exists without water. But how can one proof that such life isn't but a special case out of a bunch of other different types of life?
Actually, I think we can come out with at least one example of a "organism-like thingy" that would not require liquid water. Well, we could build a simple robot, whose "natural ecosystem" would be a junkyard (for mechanical, electric and electronic garbage). That robot would would fuel itself with solar energy, and reproduce by seeking out appropiate parts in the junkyard and building a copy of itself from them. Of course, that's just a theoretical example, I know it has many faoults, but I still hope the idea is clear - it should be indeed possible for life to exists without water.
I have also heard (sorry, I can't remember the source) that theoretically, there could be an organism whose metabolism would rely on sulphur.
So, unless scientists can proove that no life can exists without water (any life; not just Earth-like life), why do they keep looking just for water?
Unless, of course, we define "life" as "any organism functioning like Earth organisms; therefore, metabolising organic structures with enzymes, built of protein, requiring water, etc"
BTW. This question is a little bit different than Why is liquid water considered a requirement for life? . The answers there were pointing out that water is a good solvent. And I'm (also) asking why is any similar solvent considered needed. See my example above.