Planet Nine: does it exist?

[Kyng]

Just saying if the planet is a super earth in mass the core of the missing 5th gas planet would make sense and it's near destruction would explain a lot of other oddities like Venus spinning backwards and Uranus being tilted on it's side, as well as the possible origin of the asteroid belt.

Possibly - although, I always thought the Asteroid Belt was a 'failed' planet that was pulled apart by Mars and Jupiter? Or is my knowledge on that 20 years out of date?

(It could very easily be - since it was ages since I heard that, and astronomy is one of those fields where our knowledge seems to shift rapidly )