There is a planet in Outer Wilds that seems to be made almost entirely of water. The description for this planet is as follows (taken from the in-ship computer).
None of our spacecraft have ever been able to penetrate beyond the outer atmosphere
Sure enough, when I try to fly my way into the center, I can pass through the (surprisingly stormy and hazardous) atmosphere, and only seem to get a short distance into the first layer of water.
I'm at full throttle in this image, and as you can see, I'm now approaching the core at 0 m/s, which I guess means I'm stopped. I can toss probes towards the center, and they too end up hanging in underwater limbo a short distance ahead of me.
Is it possible to reach the center somehow?