八大行星有什么不同（用英语表达）急！急急急急！

The Eight Planets
　　Mike Brown

　　On August 24th 2006 the word "planet" was given its first-ever scientific definition by a vote of the International Astronomical Union. With the raising of a few yellow cards in Prague Pluto was demoted from full-fledged planet to "dwarf planet." The object 2003 UB313, sometimes called Xena, sometimes called the "10th planet," which in many ways precipitated this final debate, becomes the largest known dwarf planet. Unless astronomers revisit this issue at some point in the future, it is unlikely that there will ever be more than eight planets.

　　What was the problem with nine (or ten) planets?
　　Pluto and 2003 UB313 are significantly smaller than the other planets. If you were to start to classify things in the solar system from scratch, with no preconceived notions about which things belong in which categories, you would likely come to only one conclusion. The four giant planets -- Jupit