Planetary gears are a type of gear system that consists of a central gear, known as the sun gear, surrounded by multiple smaller gears called planet gears. These planet gears rotate around the sun gear and are typically mounted on a movable arm called a carrier. This design allows for compactness and high torque transmission, making planetary gears popular in various applications, including automobiles and industrial machinery. The outermost gear in a planetary system is called the ring gear, which encircles the planet gears. When the sun gear turns, the planet gears rotate and also revolve around the sun gear, creating a unique motion. This configuration provides advantages such as increased efficiency, reduced size, and the ability to handle heavy loads, making it a preferred choice in many mechanical systems.