As students head into science class, there is a whole new lesson to learn. How many planets are in our solar system? We learned in school there are nine. But now it's time to change the science books.
Pluto has been booted out of the planetary club. The little rock that millions of school kids learned was the ninth planet from the sun is a planet no longer, thanks to historic new guidelines adopted Thursday by leading astronomers.
After a cosmic week-long clash over what qualifies orbital masses for planetary status, the International Astronomical Union has stripped Pluto of the designation it's held since its discovery in 1930.
The decision by the prestigious international group spells out the basic tests that celestial objects now have to meet before they can be dubbed a planet.
Poor Pluto failed to make the new cut because its oblong orbit overlaps with Neptune's. It will now be a founding member of the new club of "dwarf planets."