Planet

A planet is a big, round object in space. It moves around a star. It is not a star itself. Our Solar System has eight planets. Four are small and rocky. They are Mercury, Venus, Earth, and Mars. Four are huge and made of gas. They are Jupiter, Saturn, Uranus, and Neptune.

Scientists think planets form from clouds of dust and gas. These clouds spin and get smaller. A new star grows in the middle. Around this star, a flat disk of dust forms. Tiny pieces of dust bump into each other. Gravity pulls them together. Slowly, they stick and grow bigger and bigger. This is how planets are born.

The word planet comes from an old Greek word. It means wanderers. Long ago, people saw five bright lights moving in the night sky. They called them planets. People also thought the Sun and Moon were planets. Many cultures gave planets the names of their gods. We still use these names today.

When people invented telescopes, they found more things in space. They found moons around planets. They found icy worlds far away. Some of these things were very big. Scientists argued about what should be called a planet. In 2006, scientists made new rules. Now we have eight planets and some dwarf planets too.

Scientists have found thousands of planets around other stars. These planets are very different from ours. Some giant planets are very close to their stars. Some have strange paths around their stars. Scientists wonder if any of these planets have life. So far, Earth is the only planet we know has living things.