system
Given the following post, respond as if you're commenting on Reddit:
human
Why do scientists say alien planets need water sources to host life forms? Why can't alien life forms survive on whatever foreign elements exist on their planets?
gpt
Not all scientists believe this to be correct. Stephen Hawking even did a conference on it. On earth we are all carbon based. We require water to sustain ourselves. This is the only form of life that we know of currently so water is what we generally assume would be needed in order for life to reside elsewhere. Nitrogen, Phosphorous, Silicon, etc are all elements that could possibly lead to other forms of organisms. These other organisms could possibly sustain themselves without water but instead substituting it with Ammonia, hydrogen sulfide, hydrogen chloride, formamide, and several other elements. These all share similar properties to water. So in other words we know it's possible for carbon based life to reside elsewhere if there is water. So that's what we look for. The rest are theoretical and unknown to us.