<P> There are 69 known moons of Jupiter . This gives Jupiter the largest number of moons with reasonably stable orbits of any planet in the Solar System . The most massive of the moons are the four Galilean moons, which were independently discovered in 1610 by Galileo Galilei and Simon Marius and were the first objects found to orbit a body that was neither Earth nor the Sun . From the end of the 19th century, dozens of much smaller Jovian moons have been discovered and have received the names of lovers or daughters of the Roman god Jupiter or his Greek equivalent Zeus . The Galilean moons are by far the largest and most massive objects to orbit Jupiter, with the remaining 65 moons and its rings together comprising just 0.003% of the total orbiting mass . </P> <P> Of Jupiter's moons, eight are regular satellites with prograde and nearly circular orbits that are not greatly inclined with respect to Jupiter's equatorial plane . The Galilean satellites are nearly spherical in shape due to their planetary mass, and so would be considered (dwarf) planets if they were in direct orbit around the Sun . The other four regular satellites are much smaller and closer to Jupiter; these serve as sources of the dust that makes up Jupiter's rings . The remainder of Jupiter's moons are irregular satellites whose prograde and retrograde orbits are much farther from Jupiter and have high inclinations and eccentricities . These moons were probably captured by Jupiter from solar orbits . Eighteen of the irregular satellites have not yet been named . </P> <P> The physical and orbital characteristics of the moons vary widely . The four Galileans are all over 3,100 kilometres (1,900 mi) in diameter; the largest Galilean, Ganymede, is the ninth largest object in the Solar System, after the Sun and seven of the planets, Ganymede being larger than Mercury . All other Jovian moons are less than 250 kilometres (160 mi) in diameter, with most barely exceeding 5 kilometres (3.1 mi). Their orbital shapes range from nearly perfectly circular to highly eccentric and inclined, and many revolve in the direction opposite 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). </P> <P> Jupiter's regular satellites are believed to have formed from a circumplanetary disk, a ring of accreting gas and solid debris analogous to a protoplanetary disk . They may be the remnants of a score of Galilean - mass satellites that formed early in Jupiter's history . </P>

Which of jupiter's moons is the largest