The Sun is at the center of the planets. Close to it are the inner planets - Mercury, Venus, Earth and Mars.
Mercury the planet closest to the Sun, is a cratered rock not much bigger than our Moon. It is incredibly hot and unable to support any kind of life. The atmosphere contains sodium and potassium.
Venus is the next planet from the Sun and is about the same size as the Earth. The atmosphere is made up of mainly carbon dioxide. The surface temperature can be as high as 480 degrees Celsius. There is no life of any kind on the planet Venus.
Earth is the only planet that has the conditions to support life. The surface is neither very cold nor very hot. Water can exist in all its three forms - as gas, liquid, and solid. These conditions allow plants and animals to live and reproduce.
Mars, the first planet beyond Earth is smaller than the Earth. The atmosphere is made up mostly of carbon dioxide. Water exists on this planet, but only in the form of ice. The whole planet is a red, lifeless desert.
The outer planets, Jupiter, Saturn, Uranus, and Neptune are called the gas giants. They are much larger than the Earth. The outermost planet, Pluto, is no longer classified as a planet. It is now called a dwarf Planet. It is so far away, it is a mystery.