What are the Galilean Moons?
The Galilean moons are Jupiter’s largest four moons, discovered in 1610 by the Italian astronomer and physicist using one of the earliest telescopes. The discovery of the Galilean moons, and the implications about the universe they signified, are considered a landmark event in the Renaissance. By discovering the first moons orbiting around another planet, Galileo showed that other planets possess their own gravity, supporting the Copernican heliocentrist theory published 67 years earlier. The Galilean moons were, in order of size: Ganymede, Callisto, Io, and Europa. Ganymede has a diameter of 5262 km, Callisto is 4820 km, Io is 3660 km, and Europa is 3121 km. In order of distance from Jupiter, they are Io, Europa, Ganymede, and Callisto. Ganymede is even larger than the planet Mercury, although its mass is only about half. Callisto approaches Mercury in size. For comparison, our own Moon is 3474 km in size, making it only larger than Europa. Along with the Moon, Saturn’s Titan, and Nep
Jupiter’s four largest moons were discovered by Italian astronomer Galileo Galilei in 1610. Ganymede is the largest moon in the Solar System—it is 3,273 miles (5,268 km) across. Callisto is the most heavily cratered object in the Solar System, and Io is the most volcanic. Europa is covered with a blanket of water ice that may support primitive life.
