Why two astronomers think we have a ninth planet

There are quirks at the far edge of our solar system, in the form of disturbed objects in the Kuiper belt. One explanation: Planet Nine.

Have Astronomers Found a New Ninth Planet in the Solar System

Pluto and the Solar System

How Scientists (Possibly) Found the Solar System's Ninth Planet

Planet 9: “You kill a planet, then you go out and find a new one

Weird orbits hint 'Planet Ten' might lurk at solar system edge

Why astronomers now doubt there's a Planet Nine, Space

New evidence points to giant 9th planet on solar system edge

Why astronomers now doubt there's a Planet Nine, Space

Beyond Pluto: the hunt for our solar system's new ninth planet