CoachA terrestrial planet is a planet made mostly of silicate rock and iron, with a solid surface: Mercury, Venus, the Earth and Mars. A giant planet is a planet many times more massive than the Earth, made mostly of light elements and their compounds and without a solid surface. A gas giant is a giant planet made mostly of hydrogen and helium: Jupiter and Saturn. An ice giant is a giant planet made mostly of the compounds astronomers call ices — water, methane and ammonia — under an envelope of hydrogen and helium: Uranus and Neptune.
