Footnote
a The four inner planets of our solar system—Mercury, Venus, Earth, and Mars—are called terrestrial because they have rocky surfaces. The giant outer planets—Jupiter, Saturn, Uranus, and Neptune—are composed mainly of gas.
a The four inner planets of our solar system—Mercury, Venus, Earth, and Mars—are called terrestrial because they have rocky surfaces. The giant outer planets—Jupiter, Saturn, Uranus, and Neptune—are composed mainly of gas.