I figured out the orbits in an inverse r^5 force field during a particularly productive nap in the winter of 1993. (IIRC, the orbits are closed, like those in a

I figured out the orbits in an inverse r^5 force field during a particularly productive nap in the winter of 1993. (IIRC, the orbits are closed, like those in an inverse r^2 field, but---bang!---they intersect with the center of force.)