Neptune - planet number 8 in the solar system, if you consider the distance from the sun. The average distance of Neptune from the Sun is 4.5 billion km and it is four times larger than that of the Earth (49500 kilometers in diameter). Like Uranus, Saturn and Jupiter, Neptune is a gas giant. It is actually, the smallest gas giant in the Solar system. Neptune is the name of the God of the Sea in Roman Mythology. The atmosphere of Neptune consists of methane, helium, hydrogen and water. Neptune has rings made up of tiny debris of asteroids. Most of them have the size of a car. Because of the absorption of red light by methane gas, Neptune seems blue.