Planets form as part of a protoplanetary disk around a young star. Over time, the dust and gas in the disk come together to form clumps, which eventually grow into planetesimals. These planetesimals then continue to collide and grow until they become planets. The formation of planets is influenced by the properties of the protoplanetary disk, including its temperature and density. Planets can also be classified by their atmospheric composition and their position relative to their star.

The study of planets is known as planetary science and helps us understand the formation and evolution of our solar system and the possibility of life on other planets.