No one knows when Jupiter was discovered. The planet was known to the ancients and named after the chief god of the Romans. However, it's believed that the Chinese astronomer Gan De discovered one of Jupiter's many moons in 362 B.C. Jupiter's rings were discovered in 1979 by Voyager I.
Jupiter is the solar system's largest planet. It's a gas giant that's 272,945.9 miles round at the equator. Its atmosphere is made mostly of helium and hydrogen, though scientists believe there is an Earth-sized solid core at its center. Jupiter is the fifth planet from the sun, and it takes nearly 12 Earth years to go around the sun.