I'm now working on my lunar lander program again. The core idea is to adapt Thrust gameplay for a circular planet, so that orbiting is a possibility. My goal is to release something in early December.
The top priority is to get an interesting planet to land on. I am working from these sources, albeit translating everything into two dimensions:
The basic idea I'm trying out is to define a density function over the plane, and then evaluate it to find the boundary where density crosses from negative to positive. The density function can be built up out of a variety of pieces; at the moment I'm starting with a radial increase with an offset (d = r - 1):
Layered on top of that are several octaves of Perlin's simplex noise. The first two are shown below:
I convert the implicit function to a surface by subdividing a large triangle that encompasses the planet; you can see its outline (cropped by the window rectangle) in the pictures above.
Below are the results of layering the radius function with three octaves of noise:
There are lots of other things to try; this is as far as I got last night.
The next step is to build a BSP or spatial hash in order to make the terrain solid. That should not be hard. After that I will probably want to triangulate the interior and texture it; I'm still thinking about the best way to accomplish that.
The noise functions don't guarantee that everything will be interconnected. You can see free-floating bits, as well as isolated pockets of air inside the ground. It might be nice to filter out the isolated pockets, and maybe justify the floating junks of rock by rendering a background layer to suggest that it's the cross section of an arch.