Here is a bit more on the information they used in their model to come to this unusual conclusion:

But modeling the Solar System, Nesvorny was able to “rewind” and take a look at where these rocks came from. He found that they were once under the influence of Neptune’s gravity, albeit further from the Sun; Neptune orbited at a distance of 4.2 billion kilometers (2.6 billion miles), and the kernel at 6.9 billion kilometers (4.3 billion miles). But suddenly, four billion years ago, Neptune’s orbit was shifted and it moved 7.5 million kilometers (4.7 million miles) outwards. The kernel, unable to keep up, escaped the clutches of Neptune, and remained in the same position, where it is today.

And the below video is related in that some think there may be at least one or more planets just outside our solar system.  This is the intro from the person who posted this video:

Astronomers think at least two more planets exist.Beyond Neptune.  In two studies from the UK and Spain, scientists say the planets’ existence is the only way to explain why objects are behaving as they are in the nether regions beyond Neptune (and recently demoted non-planet) Pluto, These objects—called extreme trans-Neptunian objects, or ETNOs—should be zipping around randomly but are instead doing so with “unusual symmetry,”

If nothing else this is all interesting.

thanks to iflscience.com for the great info