kuiper belt

Mysterious out-of-this world Ultima Thule is a billion miles beyond Pluto, 4 billion miles from Earth.
The New Horizons probe is hurtling toward an object nicknamed Ultima Thule in the mostly unexplored Kuiper Belt.
The planet -- which would have been our solar system's fifth giant -- had a bumpy ride on its way out, scientists say.
The missing planet bumped into Neptune before disappearing into the abyss of space, according to a new study.