just wanted to run a few ideas by you arsonide. first, as I said in the pm, it doesn't have to be perlin noise, it'll work with any set of numbers you can refer to by position, even an array as newt suggested.
so if you were planning to use gridtree, and tunnel into greater detail there's no reason this can't be adapted to that. When I have a little time, if you need me to, I can try to put this into function object form, cuz it's kindof a pain fiddling around in that formula, and also what you said about how distorted the texture gets in the distortion
but anyway. what you said about the mask might not work, because the texture would have to wrap in a circle. depending on how urgent this is, cuz I'm really busy lately, but I can help you get a workable method to reliably wrap a tileable texture around the planet in a smooth looking way. I've been working alot with distorting textures around curves and into different shapes lately. which brings me to my other idea, if you wanted, it could even be made to look like the planet surface was becoming more spherical as it became more circular, so your texture would actually bulge forward and make it look like a 3d planet, and flatten to a more 2d look as it unrolled into the sidescroller view.
anyway, gotta get to work. see ya, glad you liked it!!! It was an interesting challenge.