Scientists may have discovered a dwarf planet far beyond Neptune — an unearthing that may disprove a longstanding theory ...

Over the past decade, researchers have been puzzling through Pluto’s mysteries. Meanwhile, the New Horizons probe heads for interstellar space.

Our solar system may have a ninth planet after all, following the declassification of Pluto nearly two decades ago, researchers say. ABC News. Live. Video. Shows. Shop. Log In. Stream on.