system
Given the following post, respond as if you're commenting on Reddit:
human
Can a planet be entirely made up of water?

Meaning none of it is frozen, with no land masses and a completely liquid center. Would it remain stable? Or is something like this completely impossible?
gpt
There's nothing explicitly wrong with a planet made out of water, but it is impossible to be made entirely out of liquid water. If the planet is massive enough, it will develop a solid, pressurized core. And no matter what you do, save turning the entire waterworld into some kind of super-dense hyper-compressed magical water, there will always be gaseous water seeping off of the surface due to the vacuum. The result (if you tried) would probably resemble a very odd-looking gas giant.