Planet Nine follows Mike Brown as he begins the search for the elusive, theoretical Planet Nine at the Subaru Telescope atop Mauna Kea in Hawaii in 2016.

The New Horizons spacecraft gave us our first close-up look at Pluto, the most iconic of the dwarf planets orbiting in the icy outskirts of the solar system. This historic flyby opened a new frontier of exploration, revealing a surprisingly complex and dynamic world. Now, scientists are unraveling fresh clues about how our solar system formed - and what hidden worlds may still lie beyond Neptune.

Join astronomer Mike Brown and his team at Caltech as they track down distant dwarf planets on the frontier of space: Eris, a shimmering world once thought to be larger than Pluto; Haumea, shaped like an egg and spinning faster than any other known large object in the Solar System; and Sedna, with a mysterious, elongated orbit that carries it far beyond the Kuiper Belt into an uncharted region.

Could these extreme objects be pointing us toward an even bigger discovery-a ninth planet lurking in the shadows?

Planet Nine follows Mike Brown as he begins the search for the elusive, theoretical Planet Nine at the Subaru Telescope atop Mauna Kea in Hawaii in 2016.

The New Horizons spacecraft gave us our first close-up look at Pluto, the most iconic of the dwarf planets orbiting in the icy outskirts of the solar system. This historic flyby opened a new frontier of exploration, revealing a surprisingly complex and dynamic world. Now, scientists are unraveling fresh clues about how our solar system formed - and what hidden worlds may still lie beyond Neptune.

Join astronomer Mike Brown and his team at Caltech as they track down distant dwarf planets on the frontier of space: Eris, a shimmering world once thought to be larger than Pluto; Haumea, shaped like an egg and spinning faster than any other known large object in the Solar System; and Sedna, with a mysterious, elongated orbit that carries it far beyond the Kuiper Belt into an uncharted region.

Could these extreme objects be pointing us toward an even bigger discovery-a ninth planet lurking in the shadows?