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Scientist Claims There's Even More Evidence of Planet Nine's Existence (theverge.com)
An anonymous reader cites an article on The Verge: More evidence is pointing toward a mysterious Neptune-sized planet lurking at the outer edges of our Solar System. One of the scientists who claimed in January to have found strong evidence for a ninth planet -- temporarily named 'Planet Nine' -- now says there are even more clues that support the world's existence. Mike Brown, a planetary astronomer at Caltech University, originally concluded that Planet Nine most likely exists after studying the behaviors of six objects in the Kuiper Belt -- the large cloud of icy bodies that orbit the Sun beyond Neptune. Now Brown is claiming that another Kuiper Belt object supports his theory. The object shares some of the same behavior as the other six Kuiper Belt bodies, suggesting it has also been pushed by a large planet that is between 200 and 1,200 times the distance from the Sun to Earth.
> So.. the orbits of several comets were disturbed by something large moving through our solar system at some point in the past.
Actually, by repeatedly disturbing the orbits of these Scattered Disk objects, so their orbital parameters are opposite the proposed planet. In that location, the planet doesn't disturb them any more, so they stay put. A single pass of a rogue planet would not change the orbits of *anything* that much, and once that one pass was done with, the Scattered Disk Objects would drift away from their anti-alignment.
We see other examples of this "gravity shepherding". For example, Pluto and the Plutinos stay in a 3:2 resonance orbit with Neptune, because Neptune's gravity keeps them there.