Planet Nine: does it exist?

[Kyng]

Kyng that is the prevailing theory yes, but it's still entirely possible that it was destroyed by other forces, don't forget Jupiter wasn't always where it is today so it's possible Jupiter and mars are preventing it from reforming after a cataclysm.

Yeah, I was assuming that Mars and Jupiter were closer to one another (and, indeed, to this failed planet) when they pulled it apart.

Although, even if that was the case, I expect it'd take a lot of energy (and perhaps a lot of time) to put all the pieces back together. It's hardly surprising that they haven't re-formed on their own .