What Are the Inner Planets Made Of?

The inner planets are made of rocks and metals and are called the terrestrial planets. They are Mercury, Venus, Earth and Mars. As of 2014, Earth is the only terrestrial planet known to have life.

Mercury is the closest inner planet to the sun. It has very little atmosphere and is pockmarked with craters. It's made mostly of iron and nickel and, like Earth, is believed to have a molten iron core. The crust of Mercury is made of silicates.

Venus is notorious both for its beauty in the morning and evening skies and also for its atmosphere, which is thick with clouds made of sulfuric acid. Venus also has an iron core, but it spins so slowly that the planet doesn't have a global magnetic field like Earth. Venus is so geologically active, with many volcanoes, that its surface features change constantly.

Earth is not only made of rocks and metals, but it is also covered in water, which allows it to support life.

The red soil of Mars indicates that the iron within it has oxidized. Mars might also have liquid water, but its atmosphere is so thin that the water probably sublimates, or turns directly from water to gas. Mars seems to have water ice at its poles.