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The orbits of icy minor planets beyond Neptune are doing something very strange: they all tilt and pitch in similar ways, and maybe even cluster together on the sky. In a 2016Ìý, my collaboratorÌýÌýand I show that when gravitational forces between minor planets on eccentric orbits are included in N-body simulations, the orbits incline rapidly off the disk plane, and tilt and pitch in exactly the same way. This gravitational instability is something that a disk of eccentric orbits does on its own -- we don't need to invoke an external reason (like aÌý) for it. We do, however, predictÌýa lotÌýof minor planets in the outer Solar System, a "new Kuiper Belt" (with an order of magnitude more mass!), to defend the orbital clustering against the precessing effects of the giant planets.

We now have a whole series of papers on this topic, including an explanation of theÌýÌýand the discovery of eccentricity oscillations when we include aÌý.

We recently (April 2020) submitted a paper onÌýÌýand a letter showing that the collective gravity of extreme Trans-Neptunian Objects can result inÌý.