Inner Planets

Mercury, Venus, Earth and Mars are small, rocky planets close to the Sun.

Earth and the Moon as two small crescents against a black background, seen from Mars orbit.
Earth and Its Moon, as Seen From Mars. Credit: NASA/JPL-Caltech/Univ. of Arizona. Source, NASA media guidelines.

The four planets closest to the Sun are called the inner, terrestrial or rocky planets. They are made mostly of rock and metal, have solid surfaces and few or no moons.

Close to the young Sun it was too hot for ice to survive, so only rock and metal could clump together. That is why the inner planets are small compared with the giants farther out.

  • Mercury: the smallest planet and the closest to the Sun.
  • Venus: the hottest planet, hidden under thick clouds.
  • Earth: the only place where we know life exists.
  • Mars: the red planet with the largest volcano in the Solar System.

The image above was taken by the HiRISE camera orbiting Mars. It shows Earth and its Moon from about 205 million kilometres away.