The path to Pluto is riddled with false starts and mistaken identities, but Mother Nature has been kind to its explorers. Here's a look at some of the key moments leading up to humanity's first close-up look at Pluto.
PHOTOS: Our Dwarf Planet Dreams are Coming into Focus
Percival Lowell, an American businessman, mathematician and astronomy buff, spent the last decade of his life searching for what became known as "Planet X," a ghost world in the solar system's nether regions that had enough heft to gravitationally elbow the orbits of the two outermost giant planets, Uranus and Neptune.
He never found it, but working at the Flagstaff, Ariz., observatory that Lowell founded, astronomer Clyde Tombaugh in 1930 spotted a planet near where Lowell's calculations a quarter of a century earlier predicted Planet X should be. Though the newly found planet's mass could not be accurately measured for another 50 years, scientists came to suspect that it was too small to account for quirks in the giant planets' orbits.
The Planet X theory was officially retired when astronomers figured out that their estimates of Neptune's mass were off. With more precise data from the 1989 Voyager 2 flyby, the orbital discrepancies disappeared.