The largest planet in the Milky Way galaxy is Jupiter. It is a gas giant, primarily composed of hydrogen and helium, and boasts a diameter of about 86,881 miles (139,822 kilometers), making it more than 11 times wider than Earth. Jupiter is known for its prominent bands of clouds, Great Red Spot, and numerous moons, including the four largest known as the Galilean moons: Io, Europa, Ganymede, and Callisto. Its immense size and strong gravitational influence have made Jupiter a fascinating subject for astronomers and a key player in the solar system's dynamics.