What are planets made of?
Earth and the other three inner planets of our solar system (Mercury, Venus and Mars) are made of rock, containing common minerals like feldspars and metals like magnesium and aluminum. So is Pluto. The other planets are not solid. Jupiter, for instance, is made up mostly of trapped helium, hydrogen, and water. In our solar system, the four “gas giants” are Jupiter, Saturn, Neptune, and Uranus.