Planets are large celestial bodies that revolve around a star in fixed paths called orbits. They do not produce their own light but reflect the light of the star they revolve around. Planets are formed from leftover gas and dust after a star is born. Earth is a unique planet because it supports life due to the presence of air, water, and suitable temperature. Some planets are rocky, while others are made of gases. Planets play an important role in maintaining balance in a solar system through gravitational forces.