Our solar system may have a ninth planet after all, following the declassification of Pluto nearly two decades ago, researchers say.

A powerful new observatory is the best hope yet for finding the elusive Planet 9, a large planet that some scientists say is hidden in our solar system.

After a decade-long search, some scientists say a growing number of clues point to the existence of a hidden planet in the Kuiper Belt beyond Neptune — and they may soon have the opportunity to ...

Though Pluto has formally been considered a dwarf planet for almost two decades, it still has many lessons left for planetary scientists — including hints about how the solar system formed.