The solar system: What are planets made of?

Did You Know: Space – What are planets made of? 

In our solar system, the four inner rocky planets—Mercury, Venus, Earth, and Mars—have solid surfaces that you could walk on.

The surfaces of the two gas giants, Jupiter and Saturn, and the two ice giants, Uranus and Neptune, aren’t solid, and you could not walk on them.



Rocky planets have a hard surface, which is known as the crust. Much of the Earth’s crust is hidden by oceans.


All rocky planets have a similar structure. Each has a metallic core, or center, which is mostly made of iron.


The part of the planet between its crust and core is called the mantle.

It is made of many rocky layers.



Unlike the rocky planets, ice and gas giants don’t have a hard surface. They are made mostly of ice or gas with a small, rocky core.


Ice and gas giants have many layers of clouds. Underneath the cloud tops, the atmosphere gets thicker and thicker.

What are planets outside our solar system made of?

HD 189733b

Planets that orbit other stars are made of the same kind of stuff—rocks and gases —as the planets in our solar system.

HD 189733b is a huge gas giant like Jupiter. It is blue and rains liquid glass!


This is the most “Earthlike” planet discovered so far. It is a similar size as our planet, and scientists think that, like Earth, it might be rocky and have water on its surface.