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Pluto: Location and Orbit
Facts in Brief
| Aphelion | 7.38 x 109 km |
| Perihelion | 4.43 x 109 km |
| Minimum Distance from Earth | 4.2937 x 109 km |
| Rotational Period | 6.4 Days (1.5 x 102 Hours) |
| Orbital Period | 248* Years (9.06 x 104 Days) * The approximation of 365.256 days per year is used. |
| Orbital Inclination | 17.2o |
| Eccentricity | 0.25 |
| Axial Tilt | 122o 31" |
Relative Location
Named for the Roman god of the underworld, Pluto highly-elliptical orbit takes it the farthest from the sun of any planet. Until 1930, the 
year of its discovery, Neptune was believed to guard the frontiers. The eight-planet model, however, failed to explain the slight perturbations in the orbital motion of Uranus. Percival Lowell, an American astronomer, predicted--with erroneous calculations, it later turned out--a ninth planet that would explain away these disturbances. He began a world-wide search for "Planet X," which was eventually discovered twenty-five years later by a junior research assistant, Clyde Tombaugh. Though its discovery explained Uranus's wobbles, it left even more questions unanswered.Two major theories of Pluto's origins exist. Most astronomers believe that either Pluto is a former moon of Neptune knocked out of orbit or that it is simply a mis-classified asteroid from the Kuiper belt. (The Kuiper belt is analogous to the asteroid belt between Mars and Jupiter: a ring of millions of rocky, icy objects orbiting the Sun beyond Neptune.)