Back in 2006, the International Astronomical Union laid out the standards for defining what is and what is not a planet, and Pluto didn't make the grade. A hue and cry went up from Pluto fans and those who didn't want to learn a new mnemonic, but Pluto still remains a dwarf planet, excluded from the pantheon of the solar system. The IAU is holding its General Assembly next month, and one of the issues will be a new definition of the word "planet."
The new parameters that astronomers want for the definition will not help Pluto. It won't affect any of the planets in our solar system. But it may help define the nearly 6,000 exoplanets that have been discovered so far, and the ones yet to be discovered. Therefore, it will have to cover the definition of a star that a planet is orbiting, and stars come in all kinds. The new definition has a lower and upper limit to a planet's size, too. Those are things that we never had to ponder before, since we only knew nine, er, eight planets. Read about the proposed new definition of "planet" and what it means for interstellar research at Gizmodo.
(Image credit: NASA/JPL)
