New Horizons headed for the lonely world of Pluto on the outer edge of the solar system.
Although astronomers now call Pluto a dwarf planet, "it's actually a large place, about 5,000 miles around at the equator," says Alan Stern, principal investigator for the mission. "And it's never been explored."
Indeed, no spacecraft has ever visited Pluto or any dwarf planet.
Dwarf planet mysteries beckon to New Horizons