**Nine planets are in our solar system**: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Apart from Earth, these planets were named after the gods of Roman mythology. If you're having difficulty remembering the order of the planets, a few memory tricks can help you keep them straight.
The Inner Planets
The planets closest to the Sun are small, and are largely composed of rocks and metals.
Mercury's orbit ranges from between 29 million miles and 43 million miles from the sun. It is mostly composed of iron. Because it has no atmosphere, and orbits close to the sun, temperatures on Mercury can vary wildly, from over 400 degrees Celsius to under negative 150 degrees.
Venus is roughly the size of Earth, and orbits 67 million miles from the sun. Its thick, toxic atmosphere traps heat, making Venus the hottest planet, with temperatures that can reach over 460 degrees Celsius.
The Earth is your home planet, orbiting between 91 million and 94 million miles from the sun. Earth is dense and composed of metals such as iron and nickel. It is largely covered with liquid water, and the only planet known to support life.
Mars orbits at an average 142 million miles from the sun, and is roughly half the size of Earth. It has two visible icy poles, and appears red because it is covered in rusty, iron-composed minerals.
These four inner planets are separated from the outer planets by the asteroid belt, a ring of asteroids 92 million miles wide.
The Outer Planets
Apart from Pluto, the outer planets of the solar system are gas giants, which are largely composed of thick, swirling clouds of gas. You can use this difference to remember which planets are inner and outer.
Jupiter is the largest planet in the solar system, and has a mass greater than all the other planets combined. It orbits between 460 million and 508 million miles from the sun, and has 67 moons.
Saturn orbits between 839 and 938 miles from the sun, and is best known for its visually impressive rings, whose diameter is as wide as the planet itself. Saturn has 62 moons, the largest of which is named Titan.
Uranus orbits at an average of 1.79 billion miles from the sun, and has a distinct light blue color. It has faint rings, and orbits around the sun on its side -- its south pole is pointed directly at the sun.
Neptune is a dark blue gas planet that is smaller and heavier than Uranus. It orbits 2.8 billion miles from the sun, and has 14 known moons.
As of 2006, Pluto is considered a dwarf planet rather than a planet, but is still often considered among the nine planets. It orbits between 2.76 and 4.59 billion miles from the sun, and is composed of rock and ice. Temperatures on Pluto are cold, under negative 200 degrees Celsius.
Mnemonics for Remembering the Planets
A mnemonic is a tool you can use to help memorize the planet order. In a mnemonic you take the first letter of each planet's name and create a sentence out of them. For example:
"My Very Educated Mother Just Served Us Nine Pizzas"
You then memorize this sentence, and can recall it to remember how different planet names are arranged. Many mnemonics are available for the planet names, and you can even create your own. Check with your teacher about whether to include Pluto before you start using your mnemonic to memorize the planets.