If Planet Nine Is Out There, It May Not Be Where We Think - ScienceAlert

The hypothetical Planet Nine made a big entrance in 2016, when astronomers Konstantin Batygin and Michael Brown of Caltech published a paper in The Astronomical Journal.

Under these conditions, the baby Solar System would have almost definitely formed an inner section of the Oort Cloud, the shell of icy bodies surrounding the Solar System between about 2,000 and 100,000 astronomical units from the Sun.

The formation of giant planets such as Saturn and Jupiter would have flung debris outwards towards interstellar space; but the gravitational perturbations of passing stars would have pushed them back into the Sun's gravitational influence, so that they end up forming the inner Oort Cloud.

We tend to think of the Oort Cloud as just sort of hanging about, not doing much of anything, really, but when Batygin and Brown ran a whole bunch of new simulations, taking these physics into account, they found that objects in the inner region of the Oort Cloud may indeed move about a bit.

"Due to the long-term gravitational pull of Planet Nine's orbit, inner Oort Cloud objects evolve on billion-year timescales, slowly getting re-injected into the outer solar system?

We have simulated this process, accounting for perturbations from the canonical giant planets, Planet Nine, passing stars, as well as the galactic tide, and have found that these re-injected inner Oort Cloud objects can readily mix in with the census of distant Kuiper belt objects, and even exhibit orbital clustering.".

We won't know exactly how eccentric that orbit might be until more study can be conducted of the clustered objects, to determine which of them originated in the inner Oort Cloud; but, there's a limit to how eccentric the orbit can become before it is no longer consistent with our observations of the outer Solar System.