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== Discovery ==

== Discovery ==

On February 18, 1930, [[Clyde W. Tombaugh]] at the Lowell Observatory surveyed the sky, looking for a planet beyond [[Neptune]] (called "Planet X"). Other astronomers had inferred such an object from calculations based on an erroneous value for Neptune's mass and its orbital patterns. Tombaugh knew nothing of the error, but found an object anyway. Tombaugh's daughter Annette proposed the name of that object: Pluto.

Pluto was discovered by [[Clyde W. Tombaugh]] on February 18, 1930 at the Lowell Observatory in Flagstaff, Arizona. Tombaugh was searching for "Planet X," a planet beyond [[Neptune]] that was believed to be influencing Neptune's orbit. Percival Lowell had calculated possible positions for Planet X based on observations of Neptune's orbit. However, Tombaugh did not make use of Lowell's calculations. Instead, he used the observatory's telescope to photograph the opposition point to the sun for a year, thus conducting a full sky survey of the Zodiac. Tombaugh's daughter Annette proposed the name of that object: Pluto.

Even Tombaugh realized that Pluto was not large enough to be the predicted Planet X. Astronomers continued to search in vain for it, until [[Voyager 2]] made its flyby of [[Neptune]], and the [[Jet Propulsion Laboratory]] scientists determined from this flyby that Neptune was significantly heavier than previously supposed. Current theory predicts no more planets other than the eight now known, but still allows for many other objects, both in the classic [[asteroid]] belt and in the [[Kuiper Belt]], essentially a second belt of asteroids and [[comet]]s.

When astronomers realized that Pluto is not large enough to influence Neptune's orbit, the search for Planet X was resumed. It continued until 1989, when [[Voyager 2]] flew by [[Neptune]]. NASA scientists determine that Neptune was significantly heavier than previously supposed, invalidating earlier orbital calculations.

== The dwarf planet controversy ==

== The dwarf planet controversy ==