According to the new definition, a full-fledged planet is an object that orbits the sun and is large enough to have become round due to the force of its own gravity. In addition, a planet has to dominate the neighborhood around its orbit.
Pluto has been demoted because it does not dominate its neighborhood. Charon, its large "moon," is only about half the size of Pluto, while all the true planets are far larger than their moons.
In addition, bodies that dominate their neighborhoods, "sweep up" asteroids, comets, and other debris, clearing a path along their orbits. By contrast, Pluto's orbit is somewhat untidy.
They decided it was too small because it big enough to absorb all the smaller objects in its orbit. But maybe it is, I mean, it takes millions of years for that process to occur. Also they didn't want to consider all the other dwarf planets they were finding planets too.
1 year ago
Last edited at 2:36PM on 11/11/2012
The main reason Pluto's status was changed was because it turned out to be just one of hundreds of similar minor bodies orbiting the Sun in roughly the same belt. Similar in many ways to the items in the Asteroid Belt - Pluto was no longer unique or special. Pluto turned out to be not even the biggest of the group - only the first to be discovered. But we have a probe headed Pluto's way which will reach it in a year or two for close-up analysis and photos. This has ALREADY discovered an exciting new fact about Pluto you can find for yourself if you access NASA's website....