Astronomers have always been fascinated by the gas giant Jupiter. A planet over 1000 times the size of Earth with 63 natural moons, 4 of whom are nearly as big as planets themselves, Jupiter and its moons are considered to be a mini solar system and are popularly known as the Jovian system.
Jupiter's massive size and gravitational pull have led to some unique features on the planet's 4 largest moons, Io, Europa, Ganymede, and Callisto. They are also known as the Galilean moons as they were discovered by Galileo Galilei in January 1610 and were the first satellites found to orbit a planet other than Earth. While Io is known to be extremely dry with over 400 active volcanoes, scientists believe that Europa, Ganymede and Callisto have subsurface oceans below their icy surfaces which may harbor life.
