There are 97 knownmoons of Jupiter, as of 30 April 2025.Jupiter has the second largest number ofmoons of anyplanet in theSolar System.[1][2][3]
The most massive of the moons are the fourGalilean moons, which were independently discovered in 1610 byGalileo Galilei andSimon Marius. They were the first objects found to orbit a body that was neither Earth nor the Sun. The Galilean moons are by far the largest and most massive objects to orbit Jupiter. The other 91 known moons andthe rings together make up just 0.003% of the total orbitingmass. The four areIo,Europa,Ganymede andCallisto. They are roughly the same size asEarth's moon, some are a bit bigger, some are smaller.
From the end of the 19th century, dozens of much smaller Jovian moons have been discovered. All these are less than250 kilometres (160 mi) indiameter, with most barely exceeding5 kilometres (3.1 mi). Theirorbital shapes range from nearly perfectly circular to highlyeccentric andinclined. Many revolve in the directionopposite to Jupiter's spin (retrograde motion).Orbital periods range from seven hours (taking less time than Jupiter does to spin around its axis), to some three thousand times more (almost three Earth years).
