24-08-06 Pluto is NOT a planet (Prague) <br /> <br />PLUTO DECLARED A DWARF PLANET: Today at the International Astronomical Union (IAU) General Assembly in Prague, astronomers decided that the Solar System has eight planets, and Pluto is not one of them. Instead, Pluto is a "dwarf planet." <br />To be a planet, the assembly ruled, a world must meet three criteria: <br />(1) It must have enough mass and gravity to gather itself into a ball. <br />(2) It must orbit the sun. <br />(3) It must reign supreme in its own orbit, having "cleared the neighborhood" of other competing bodies. <br />So, e.g., mighty Jupiter, which circles the sun supreme in its own orbit, is a planet--no adjective required. Pluto, on the other hand, shares the outer solar system with thousands of Pluto-like objects. Because it has not "cleared its own neighborhood," it is a dwarf planet. <br />This decision clarifies the vocabulary of planetary astronomy while simultaneously upturning 76 years of "Pluto is a planet" pop-culture. Will non-specialists heed Pluto's demotion? That remains to be seen. Meanwhile, according to the IAU, the Solar System has eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune; and three dwarf planets: Ceres, Pluto and 2003 UB313. <br />Source : www.spaceweather.com <br />Affiliated site of the NASA
