The largest planet in the solar system is Jupiter. This gas giant is known for its immense size, possessing a diameter of about 86,881 miles (139,822 kilometers) and being over 11 times the diameter of Earth. Jupiter is primarily composed of hydrogen and helium, with a thick atmosphere characterized by its Great Red Spot, a massive storm that has persisted for centuries. The planet has a strong magnetic field and numerous moons, with over 79 confirmed, including the four largest known as the Galilean moons: Io, Europa, Ganymede, and Callisto. Jupiter's size, mass, and dynamic weather patterns make it a fascinating subject of astronomical study.