Our solar system is the sun and everything that orbits around it: eight planets (including Earth), their moons, asteroids, comets, and countless smaller objects, all held together by the sun's gravity. The sun sits at the center, containing 99.8% of all the mass in the solar system, while everything else circles around it in vast, invisible paths called orbits.

The planets travel in order from the sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The inner four planets are small and rocky, while the outer four are huge worlds made mostly of gas and ice. Between Mars and Jupiter lies the asteroid belt, a region filled with millions of rocky chunks left over from when the solar system formed 4.6 billion years ago.

Beyond Neptune, in the cold outer reaches, lies the Kuiper Belt, home to icy objects including Pluto, which scientists reclassified from a planet to a “dwarf planet” in 2006. Even farther out, the Oort Cloud contains trillions of icy bodies, some of which occasionally fall inward to become comets with spectacular tails.

Our solar system is just one of billions in the Milky Way galaxy.