After some searching, I came across a free Unity Asset store add-on called Simple Dynamic Clouds by Butterfly World. It’s a very simple dynamic cloud effect that incorporates moving UV coordinates to simulate fractal Brownian motion (FBM) using some specialized texture maps. However, it was too simple to use as-is as it generated only the color (albedo). So… I went into the code and added support for bumps (normals) and specular lighting. That made it look much better.
To add the clouds to the game, I created a thin shell around each planet and applied the new clouds material and shader to it. The atmospheric density of each planet controls how thick the cloud layer appears. Also, if the planet is a molten planet, the clouds will appear dark instead of white and fluffy.
Here are some screenshots! All of this is included in the latest game download. Note: The clouds animate very slowly – you’ll see different patterns form up and dissipate.