By Donna Fuller
Updated Mar 24, 2022
Our solar system comprises eight planets, grouped into inner and outer sets. In order of distance from the Sun, the inner planets—Mercury, Venus, Earth, and Mars—are followed by the Asteroid Belt and then the outer giants: Jupiter, Saturn, Uranus, and Neptune.
According to the Beacon Learning Center, the inner planets are rocky, composed mainly of silicate rocks and metals, earning them the designation “terrestrial.” The outer planets are gas giants, dominated by hydrogen and helium, with denser cores of rock and ice—hence the term “Jovian.”
Terrestrial planets are relatively compact, all with diameters under 8,000 mi. In contrast, the smallest gas giant, Neptune, measures about 30,000 mi across, making the outer planets vastly larger yet far less alike in scale.
All rocky planets exhibit volcanic structures and impact craters, though Earth’s active geology and erosive forces have erased many of its scars. The gas giants lack solid surfaces; their “landforms” are atmospheric bands and storm systems.
The inner planets complete a full rotation in 24 hours or more—Venus taking an astonishing eight Earth months. The gas giants spin much faster, each day lasting fewer than 17 hours, as noted by The Nine Planets.org.
None of the inner planets possess rings. Mercury and Venus have no moons, Earth has one, and Mars has two. All outer planets host extensive ring systems composed of icy particles and boast numerous natural satellites.
