Which of the following is classified as a dwarf planet?

Which of the following is classified as a dwarf planet?

• A. Mercury
• B. Venus
• C. Pluto
• D. Mars

Answer: (C)

A dwarf planet is a body that orbits the Sun, is nearly round in shape due to its own gravity, but has not cleared its neighboring region of other objects. Pluto fits this description: it orbits the Sun and is large enough to become rounded, but it lies in the Kuiper Belt with many other objects, so its gravity hasn’t cleared that area. In 2006 the IAU defined this category and placed Pluto there. The other rocky worlds—Mercury, Venus, and Mars—are planets that have cleared their orbits, so they aren't dwarf planets.

A dwarf planet is a body that orbits the Sun, is nearly round in shape due to its own gravity, but has not cleared its neighboring region of other objects. Pluto fits this description: it orbits the Sun and is large enough to become rounded, but it lies in the Kuiper Belt with many other objects, so its gravity hasn’t cleared that area. In 2006 the IAU defined this category and placed Pluto there. The other rocky worlds—Mercury, Venus, and Mars—are planets that have cleared their orbits, so they aren't dwarf planets.