Scientist 1

Based on perturbations in Neptune's orbit, the search for a ninth planet was conducted, and Pluto was discovered in 1930. Pluto orbits the sun just as the other eight planets do, and it has a moon, Charon, and a stable orbit. Based on its distance from the sun, Pluto should be grouped with the planets known as gas giants. In addition, Pluto, like the planet Mercury, has little or no atmosphere. Pluto is definitely not a comet because it does not have a tail like a comet when it is near the sun. Pluto is also not an asteroid, although its density is closer to an asteroid than to any of the other planets. Pluto is a planet because it has been classified as one for more than 60 years since its discovery.

Scientist 2

Pluto should no longer be classified as a planet based on new evidence that has come to light in the last few years. When Pluto was first discovered, nothing was known about its orbit or its composition. Pluto has an orbit that is not in the same plane as the other planets (i.e., it is tilted) and its orbit is more eccentric, or elongated than any other planet's orbit. Pluto orbits the sun in the outer solar system, and so should be similar in size and composition to the gas giants, but it is not. Pluto lacks the rings that all other gas giants possess. Also, Pluto's moon is larger than any other moon relative to its parent planet. In recent years, new objects have been found that belong to the Kuiper Belt, a region of small, solid icy bodies that orbit the sun beyond the orbit of Neptune and Pluto. A large object called Quaoar has recently been discovered that has a density nearly identical to Pluto, Charon, and Triton. Based on these facts, I conclude that Pluto is a Kuiper Belt Object.