[ploo-toh] 
| 1. | Classical Mythology. a name given to Hades, under which he is identified by the Romans with Orcus. |
| 2. | Astronomy. the planet ninth in order from the sun, having an equatorial diameter of about 2100 miles (3300 km), a mean distance from the sun of 3.674 billion miles (5.914 billion km), a period of revolution of 248.53 years, and one known moon, Charon. |
| Plu·to (plōō'tō) n.
[Latin Plūtō, Plūtōn-, from Greek Ploutōn, from ploutos, wealth (from the belief that the underworld was the source of wealth from the ground); see pleu- in Indo-European roots.] |
The Roman name of Hades, the Greek and Roman god of the underworld and ruler of the dead.
Note: The planet Pluto is usually the most distant planet in the solar system.
In astronomy, the smallest of the major planets, usually ninth from the sun. Pluto was discovered in 1930 and is named for the Roman god of the underworld. (See solar system)
Note: Astronomers in the late nineteenth century, thinking they saw disturbances in the orbits of Uranus and Neptune, suspected that there was a ninth planet, not yet discovered, exerting gravitation on the other two. In the early twentieth century, astronomers searched for that planet and found Pluto. Ironically, Pluto is much too small to be the planet they sought.
Note: Pluto's orbit is a stretched ellipse, unlike the orbits of the other major planets, which are nearly circular. As a result, for a period ending in 1999, Pluto was actually closer to the sun than Neptune.
Note: There is some debate among astronomers as to whether Pluto should really be classified as a planet or should instead be considered a large asteroid-like body.
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