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 like the other eight planets, 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 sixty years since its discovery.Which argument supporting the classification of Pluto as a planet is the weakest?

Correct answer: E. Pluto has been classified as a planet for more than sixty years since discovery

• A. Pluto orbits the sun just like the other eight planets
• B. Pluto has a moon
• C. Pluto has a stable orbit
• D. Pluto, like the planet Mercury, has little or no atmosphere
• E. Pluto has been classified as a planet for more than sixty years since discovery

Last updated 3 September 2026