Which grouping includes the outer solar system planets?

• A. Mercury, Venus, Earth, Mars
• B. Pluto, Haumea, Eris, and Ceres
• C. Earth’s Moon and the planets
• D. Jupiter, Saturn, Uranus, and Neptune

Answer: (D)

Outer solar system planets are the four giant worlds beyond the asteroid belt: Jupiter, Saturn, Uranus, and Neptune. They’re much farther from the Sun and far larger than the rocky planets closer in, and they’re mostly gas or ice rather than rock. This set uniquely groups the outer planets together, distinguishing them from the inner rocky planets—Mercury, Venus, Earth, and Mars—and from dwarf planets and smaller bodies like Pluto, Haumea, Eris, and Ceres. It also isn’t just Earth’s Moon mixed with planets, which isn’t a coherent planetary group. So the grouping that lists Jupiter, Saturn, Uranus, and Neptune correctly represents the outer planets.