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== Principal discovery ==

== Principal discovery ==

Shortly after he moved to arizona, the now 24-year-old Tombaugh made the discovery for which the world will always remember him. He was searching for a "Planet X" beyond [[Neptune]]. Other astronomers had predicted "Planet X" 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. His daughter Annette named the object Pluto.

Shortly after he moved to arizona, the now 24-year-old Tombaugh made the discovery for which the world will always remember him. He was searching for a "Planet X" beyond [[Neptune]]. Other astronomers had predicted "Planet X" 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. This happened on 18 February 1930. His daughter Annette named the object Pluto.

Tombaugh knew even then that Pluto was not large enough to be the predicted Planet X. Eventually the [[Voyager 2]] flyby returned data that allowed [[Jet Propulsion Laboratory]] mission controllers to determine that Neptune had more mass than astronomers had supposed. (Today the New Horizons flyby established the mass of Pluto, among other physical and orbital characteristics.)

Tombaugh knew even then that Pluto was not large enough to be the predicted Planet X. Eventually the [[Voyager 2]] flyby returned data that allowed [[Jet Propulsion Laboratory]] mission controllers to determine that Neptune had more mass than astronomers had supposed. (Today the New Horizons flyby established the mass of Pluto, among other physical and orbital characteristics.)