What dictates that extra terrestrial life requires water in the same way as we do? Even on earth we have fish who can’t live in the open air, and people who can’t live underwater.
What is to say that ET can’t eat space rocks to obtain all of its nutrients, or even more, what is to say that they require nutrients at all?
Edit: Thanks for all the wonderful answers. Makes perfect sense. They aren’t so much saying we HAVE to have water to create life, more that we only know how that works and looking for the unknown in the vast expanse that is the universe would be the worlds largest needle in a haystack game.
In: Planetary Science
So, there is a lot going on here. We’re looking for signs of life. Obviously you can conceive of life in many ways but we know of only one way it does work — carbon based life. That kind of life needs water for celular processes to work.
Is it possible there are other life forms that are not carbon based? Yes, indeed there are other possible bases for life — silicon, and I’ve also seen metal oxides being hypothesized to be able to be the basis of a form of life.
But again, those are hypothesized life forms. They would exist in very different forms and conditions than ours. As far as I know we are looking into investigating possible silicon based life form on Titan which has a lot of amonia to act as a solvent.
Aso to your other question — how do we know that life needs nutrients. Well that’s more simple to explain. You can’t have something that makes any kind of action function — living cell basically being alive, cellular processes and such, without expending energy. Energy is a must, and you get energy with chemical procceses. For these processes you need to expend some nutrients. No nutrients, no processes possible without the organism dying in short order.
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