After experimenting further, I thought it was just a regular planet in darkness. There is no atmosphere and the sun has no power (regular lights work). There is nothing to see below the ground, unless you make the shaders luminous, when you will see a general glow. The Y values go crazy (below the terrain Y is some 12000).
It seems that, when you are on the surface of the planet, you are also inside it. The "normal" looking part of the terrain has a bulgy look. If you go further above, you get what looks like "camera inside the terrain" artifacts (maybe it's the mountains that have decided to rise), until, in the distance, most of the planet disappears. Turning around the camera and lighting the sides, what looked like artifacts, becomes a group of rocks dancing all over (or the side wall of the terrain?). I changed the colour of the "rock" shader (which has a minimum slope of 30) to red and that is what constitutes most of the dancing rocks. After increasing the light intensity, the rest of the terrain came into view, so the whole has a cave look. Of course, one can't be sure which is which, especially whether there is perpendicular terrain or it is all an illusion.
The preview sometimes shows very different from the final render.
Helen
Helen
