Jupiter has 63 moons! Some are very small and others are larger than Pluto. The four largest moons are called the Galilean moons because they were discovered by Galileo Galilei in the year 1610. Ganymede is the largest moon and it is bigger than Mercury. It is the ninth largest object in our solar system. The other three Galilean moons are Io, Europa, and Callisto and all are larger than Pluto. The 59 smaller moons tend to be less than 160 miles in diameter. Some of these smaller moons have irregular (non-spherical) shapes and astronomers theorize that they have originated from passing asteroids that were pulled into Jupiter’s’ orbit by gravity.
In February 2007, NASA’s New Horizons spacecraft flew near Jupiter and took pictures of Ganymede, Io, Europa and Callisto. Click here to see those pictures.