9781422283721

  The near planets   were formed very much   like the Earth. Planets Like Ear th

Mercury, Venus, and Mars are known as the terrestrial, or Earth-like planets. This is not because they look like the Earth, but because they are similar to the Earth in how they are formed. The Earth is made up of rock and metal, mainly iron. Geologists—the scientists who study the Earth—tell us that the Earth is made up of a number of different layers. They found this out by studying the way earthquake waves travel through the Earth. On top is the crust , a thin layer of hard rock. Underneath there is a much thicker layer of heavier rock, called the mantle . Underneath that, in the center of the Earth, is the core , which is made up mainly of iron. The outer part of the core is liquid.

Inside the planets Astronomers cannot find out directly what the terrestrial planets are like inside. But they think that the planets must be similar to the Earth because they formed at the same time and in the same way. They have a crust and a mantle made up of rock, and an iron core. The size of these layers varies from planet to planet.

∆ Venus probably has a mantle and core about the same size as those of the Earth.

∆ Mercury has a thin mantle but a thick core.

8