Poor, puny Pluto. After it was discovered in 1930, it basked in the glory of being named the ninth planet in the solar system. But in the years since, astronomers have debated whether Pluto truly is a planet. After all, it is smaller than other planets, has a strange tilt and travels in an odd orbit. Last week, scientists met in Prague, Czech Republic, to decided Pluto's fate. The International Astronomical Union voted on guidelines that define a planet. The result: Pluto is not a planet.
About 2,500 astronomers from 75 countries met in Prague. Some scientists proposed expanding the number of planets to 12. Pluto, its moon Charon, and two other objects, Xena and Ceres, would be planets. In the end, the astronomers decided that only Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune fit the definition of "classical planets." They are celestial bodies in orbit around the Sun. They are massive enough to be nearly round. Also, each has its own orbit. Pluto fails because its orbit overlaps Neptune's path.
All is not lost for Pluto. It has been reclassified a "dwarf planet." And that's good news for planet hunters. "Many more Plutos wait to be discovered," says Richard Binzel, a professor at the Massachusetts Institute of Technology, in Cambridge.