system
Given the following post, respond as if you're commenting on Reddit:
human
Can a planet exist with a sphere, like Saturn's rings but a sphere instead?
gpt
It's unlikely you'd find a planet with a spherical shell of stuff around it, unless it was artificially designed.

All of the rocks and chunks of ice and stuff would be orbiting around the planet, with roughly circular orbits. The centres of these circular-ish orbits is always the centre of the planet. So if you imagine some particle that's currently north of the equator, then on the other side of its orbit it's going to be south of the equator.

What this means is that these orbits intersect with each other. The shell isn't rotating like a single solid body. Instead, the particles will be crashing into each other. This isn't a stable system. The particles will be losing energy and transferring angular momentum through these collisions. This will keep on going until they reach a stable state where they aren't colliding very much anymore. This stable state is a flat ring or disc - here, you can have particles all in circular orbits without crashing into each other. So a shell of particles would settle down into a ring.

You *could* artificially design it to be stable, by setting up satellites with orbits at different angles and distances that are perfectly arranged to not collide. But you wouldn't expect this to happen naturally.

If you're imagining a *solid* spherical shell, then that would definitely have to be artificial. But even then, it's not really stable. It turns out that the gravity from a shell perfectly cancels out in all directions. This means that any slight drift between the planet and the shell is not corrected - they will drift towards each other until they collide. Any science-fiction solid Dyson sphere would need some sort of thrusters to keep it stable.