Not necessarily. We understand lots of the underlying orbital physics and know from stellar lifecycles how much of each element to expect. From there you can ru

Not necessarily. We understand lots of the underlying orbital physics and know from stellar lifecycles how much of each element to expect. From there you can run the math on radius and density and only be left with so many possibilities of what the thing is made of. It’s not certainly water, just one of the likely possibilities. An interesting hypothesis that could actually be tested by atmospheric spectroscopy using Webb.