Our Solar System May Have Had A Fifth 'Giant' Planet

I thought this was interesting.

Our Solar System May Have Had A Fifth 'Giant' Planet

That's one I hadn't heard before. I have heard it suggested that there was another rocky planet between Jupiter and Mars, which was torn apart and created the asteroid belt.

I had heard that too. A fifth gassy planet, bouncing off Neptune and heading for parts unknown sounds a little too Velikovskian.

I heard that too. But it didn't actually happen.

wikipedia wrote:

The asteroid belt formed from the primordial solar nebula as a group of planetesimals, the smaller precursors of the planets, which in turn formed protoplanets. Between Mars and Jupiter, however, gravitational perturbations from Jupiter imbued the protoplanets with too much orbital energy for them to accrete into a planet. Collisions became too violent, and instead of fusing together, the planetesimals and most of the protoplanets shattered.