A solar system is a collection of planets revolving around a central star. It includes all their moons, and the comets, meteors, dust and gas in between. Each galaxy has billions of solar systems. Our solar system extends trillions of miles out into outer space. It ends in an icy cloud called the Oort Cloud. The planets in our solar system include (from the sun outward): Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune (Pluto was thought to be the ninth planet until recently). All the planets of our solar system orbit the sun.