Terrestrial Planet Facts

The four innermost planets of our solar system (Mercury, Venus, Earth and Mars) are called the “terrestrial” planets. The name comes from the word “telluric” derived from the Latin words “terra” and “tellus”, used to refer to Earth. They are made mostly of silicate rocks and metals, with solid surfaces and atmospheres that range from thick (on Venus) to very thin (on Mercury). Earth is the only one with liquid oceans, although Mars may have had them in the past.

Find out more about the inner planets by selecting one below:

Facts about the Terrestrial Planets

• The terrestrial planets in our solar system orbit relatively close to the Sun, this gives them their other name; the “Inner Planets”
• Earth is the most hospitable to life. Mars may have supported life in the past, but there is no evidence that conditions have ever been life-friendly on Mercury or Venus.
• Each of the terrestrial planets has a central core made mostly of iron. The layer above the core is called the “mantle” and is usually made of silicate rocks. These are rocks rich in silicon and oxygen. The terrestrial planets are also sometimes referred to as the “rocky” planets.
• The surfaces of terrestrial planets have mountains, craters, canyons, and volcanoes. About 75% of Earth’s surface is covered in water. Both Mars and Earth have permanent polar ice caps.
• None of the terrestrial planets in our solar system have ring systems. Planetary scientists suspect that they may once have had rings that have since disappeared.
• There is one dwarf planet considered to be terrestrial-type world: Ceres. It has a rocky core and an outer mantle, with surface features such as craters and mountains.
• Terrestrial planets exist around other stars. Data from the Kepler mission suggest Earth-sized and so-called “super-Earth” worlds exist throughout the galaxy. There could be up to 40 billion such exoplanets in the Milky Way.

Terrestrial Planet Size & Orbits

Name	Diameter	Distance from Sun	Length of Year
Mercury	4,879 km	57,909,227 km	88 Earth days
Venus	12,104 km	108,209,475 km	225 Earth days
Earth	12,742 km	149,598,262 km	365.24 days
Mars	6,779 km	227,943,824 km	687 Earth days