Measuring the Mean Plane of the Distant Kuiper Belt

"We find a warp relative to the invariable plane at semimajor axes of 80 - 400 AU (98% confidence) and 80 - 200 AU (96% confidence), but not at 50 - 80 AU or 200 - 400 AU. If it is not spurious, a possible explanation for this warp is an unseen planet in the outer solar system. With n-body simulations, we find that a planet with mass between that of Mercury and the Earth, semimajor axis in the range 100 - 200 AU, and inclination ≳10∘ to be the most likely cause of the warp; however, parameters outside of these ranges are still possible."