I decided to branch out and try designing something for a full color powder printer. The STL really doesn't do it justice; if you have Windows 8.1 (or 10), you can open the 3MF with 3D Builder, which I work on.
I used NASA images: the Blue Marble for the earth, and the Hubble Deep Field for the knot. The earth is forever captured, but can roll around a knot-shaped orbit. See my video of the finished print.
One of the cool features we added to 3D Builder is "Buy Print", which allows you to make things in materials we can't manage at home. I printed this in Colorstone for $172 (I know, not as cheap as we'd like, but pretty good for a 6 inch wide piece).
This object was created with Matlab, and my .m script is in the downloads section. I generally use OpenSCAD for design, but these curvy forms are not well suited to it. Instead a made a recursive knot script, that builds a 3-1 knot around the path of a 2-3 knot, along which the earth rolls. Doing my own texture mapping was a new and interesting challenge.
The 3MF contains all the texture info and such. 3D Builder will open it (and hopefully more 3D apps soon as well). I work on this format, since STL and OBJ are somewhat lacking as 3D printing formats.