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. Last Updated: 07/27/2016

Pluto Gets Planethood Revoked

PRAGUE -- Pluto was stripped of its status as a planet on Thursday when astronomers from around the world redefined it as a "dwarf planet," leaving just eight classical planets in the solar system.

Pluto is no stranger to controversy. In fact, it's been dogged by disputes ever since its discovery in 1930.

Many astronomers contend the ninth rock from the sun -- officially downgraded to "dwarf planet" status Thursday by the International Astronomical Union -- never deserved to be a full planet in the first place.

Discovered by Clyde Tombaugh of Arizona's Lowell Observatory, Pluto was classified as a planet because scientists initially believed it was the same size as Earth. It remained one because for years, it was the only known object in the Kuiper Belt, an enigmatic zone beyond Neptune that's teeming with comets and other planetary objects.

Pluto got an ego boost in 1978 when it was found to have a moon -- Charon. But in the 1990s, more powerful telescopes revealed numerous bodies similar to Pluto in the neighborhood.

That prompted some galactic grumbling from astronomers who began openly attacking Pluto's planethood.

The definition of a planet approved after a heated debate among some 2,500 scientists from the IAU meeting in Prague drew a clear distinction between Pluto and the other eight planets.

The scientists agreed that to be called a planet, a celestial body must be in orbit around a star while not itself being a star.

It also must be large enough in mass for its own gravity to pull it into a nearly spherical shape and have cleared the neighborhood around its orbit.

Pluto was disqualified because its oblong orbit overlaps with Neptune's.

The new definition -- the first time the IAU has tried to define scientifically what a planet is -- means a second category, called "dwarf planets," has been created, as well as a third category for all other objects, except satellites, known as small solar system bodies.

From now on, traditional planets will be restricted to eight: Mercury, Earth, Jupiter, Saturn, Neptune, Venus, Mars and Uranus.

(Reuters, AP)