Hi, I am Reinder: a really long-time lurker of this forums.
Last week I made a fragment shader showing a seamless space-to-planet flight, showing asteroids, sea, and terrain. You can view the shader (and the code!) online here: https://www.shadertoy.com/view/4tjGRh
You need a really good graphics card and start chrome without angle (or use a mac) to run the full shader. The shader is really heavy because it is executed each frame for each pixel. No state, textures or models are used. Everything is procedural created (for each frame, each pixel) by the shader.
I have also rendered a short movie of this shader, which you can find here: https://youtu.be/VVrPhvfAXko