A planetary system consists of a star and the celestial bodies that orbit it, including planets, moons, asteroids, and comets. The most well-known example is our own Solar System, which includes the Sun and eight planets, such as Earth and Mars. These systems can vary greatly in size and composition, with some having multiple stars or a large number of planets. Planetary systems form from clouds of gas and dust in space, known as nebulae. Over time, gravity causes these materials to clump together, eventually forming stars and their orbiting bodies. Scientists study these systems to understand the formation of planets and the potential for life beyond Earth.