Astronomy
The Possibility of a Ninth Planet in the Solar System
Quick fact
In 2016, astronomers proposed that a planet roughly ten times more massive than Earth, orbiting dozens of times farther from the Sun than Neptune, could explain the strange, clustered orbits of several distant icy objects—even though it has never been directly observed.
Why this is interesting
Imagine a giant planet hiding in the dark outskirts of our solar system, so distant that we haven't seen it directly, yet its gravity may be reshaping the orbits of other worlds. What could be out there?