In this topic you will learn about the planets close to the Sun.

The solar system is a system made up of the Sun and all of the objects that orbit the Sun. The nine planets that orbit the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. We can see some of the planets in the night sky, but they do not make their own light. They reflect light from the Sun.

The inner planets are Mercury, Venus, Earth, and Mars. These planets are smaller than the other planets. The inner planets are made up of rock-like materials. The inner planets are closer to the Sun than the outer planets are, and they are also much warmer.

Mercury is less than half the size of Earth. Mercury does not have much of an atmosphere. An atmosphere is a layer of gases that surrounds most planets. Mercury does not have much air or water. The side of Mercury that faces the Sun is very hot, but the other side is very cold.

Venus is almost as large as Earth. Venus has no water, but it does have an atmosphere. The atmosphere is made up of mostly carbon dioxide.

Earth is the only planet known to have living things. Earth has water and oxygen, which living things need.

Mars is about half as wide as Earth. Its reddish surface makes it known as "the red planet." It has a thin atmosphere made up of mostly carbon dioxide. Mars has craters. It also has volcanoes that are no longer active.

Scientists learn about the planets by looking at them through telescopes. A telescope is a tool that gathers light to make faraway objects look larger, closer, and clearer. Telescopes gather light with mirrors and lenses. A lens is a curved piece of glass.