One of our planets may be missing, and it could explain why the solar system looks the way it does

Our solar system has two ice giants, Uranus and Neptune, but there may have been a third. According to a new study published in the journal Icarus, this extra world might have triggered a violent planetary shuffling billions of years ago that could have disrupted some of Jupiter's and Uranus's moons and possibly led to the formation of others.

Raccontata daphys.org