"We chose to reclassify Pluto in part because it is part of a larger body of objects which we call the 'Kuiper Belt,'" said IAU spokesman James Brown. "Since Pluto is too puny to clear this area of debris, we felt that a new designation was necessary to distinguish Pluto from proper planets like Venus and Neptune." Brown went on to explain the motivation which drove the IAU's decision regarding Earth. "As with Pluto, the way we see Earth's place in the solar system must change as new discoveries are made. Earth was once regarded as the center of the universe but as science progressed, our view of Earth's place in the universe had to change. As more and more Near Earth Objects (NEOs) have been discovered it appears that Earth, despite its much larger mass and gravity, like Pluto is not able to completely clear the neighborhood around its orbit. While many NEOs like Apophis will probably either collide with Earth or be ejected from their orbits by Earth's gravity, there are also enough objects like Cruithne with weird but stable orbits that we feel that a new classification was necessary to describe Earth's place in the solar system."
A second vote to decide whether or not Jupiter should be promoted from a "planet" to a "dwarf brown dwarf" has been scheduled for the IAU's winter meeting in December.