It would have been knocked into an eccentric orbit early in the Solar System's formation (when we had a lot more planets).
It couldn't have formed that far out. We know Uranus and Neptune are too far away - they formed closer in than they are now, and interactions with Saturn and Jupiter pushed them out. In fact, there's evidence that they switched places (Neptune originally being closer). Planet Nine could have been thrown into an eccentric orbit during this time.
It couldn't have formed that far out. We know Uranus and Neptune are too far away - they formed closer in than they are now, and interactions with Saturn and Jupiter pushed them out. In fact, there's evidence that they switched places (Neptune originally being closer). Planet Nine could have been thrown into an eccentric orbit during this time.
Here's a relevant wikipedia article: https://en.wikipedia.org/wiki/Nice_model