Which statement correctly defines a dwarf planet?

Which statement correctly defines a dwarf planet?

• A. A body that orbits the Sun, is nearly round, and has cleared its neighborhood.
• B. A body that orbits the Sun, is nearly round, but has not cleared its neighboring area.
• C. A small body that orbits a planet
• D. A star that orbits the Sun

Answer: (B)

The statement being tested captures the definition used for dwarf planets: an object that orbits the Sun, is nearly round in shape, and has not cleared its neighboring region of other debris. Being nearly round means its gravity is strong enough to pull it into a spheroidal form, which sets it apart from many smaller, irregularly shaped bodies. Not clearing its neighborhood means it hasn’t dominated its orbital zone; there are other objects of similar size nearby in the same region, unlike true planets that have cleared out most other debris along their orbits. For comparison, a body that has cleared its neighborhood would be classified as a planet, a small body that orbits a planet is a moon, and a star is not a planet at all. Dwarf planets include examples like Pluto or Ceres, which fit all three criteria.

The statement being tested captures the definition used for dwarf planets: an object that orbits the Sun, is nearly round in shape, and has not cleared its neighboring region of other debris. Being nearly round means its gravity is strong enough to pull it into a spheroidal form, which sets it apart from many smaller, irregularly shaped bodies. Not clearing its neighborhood means it hasn’t dominated its orbital zone; there are other objects of similar size nearby in the same region, unlike true planets that have cleared out most other debris along their orbits. For comparison, a body that has cleared its neighborhood would be classified as a planet, a small body that orbits a planet is a moon, and a star is not a planet at all. Dwarf planets include examples like Pluto or Ceres, which fit all three criteria.