There are 67 confirmed moons of Jupiter. This gives Jupiter the largest number of moons with reasonably secure orbits of any planet in the Solar System. The most massive of them, the four Galilean moons, were discovered in 1610 by Galileo Galilei 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, conquests, or daughters of the Roman god Jupiter, or his Greek equivalent, Zeus.
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 having planetary mass, and so would be considered dwarf planets if they were in direct orbit about 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.
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 having planetary mass, and so would be considered dwarf planets if they were in direct orbit about 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.
FOUR MAJOR MOONS OF JUPITER
Io is the innermost of the four Galilean moons of the planet Jupiter. It is the fourth-largest moon, has the highest density of all the moons, and is the driest known object in the Solar System. It was discovered in 1610 and was named after the mythological character Io, a priestess of Hera who became one of Zeus's lovers.
With over 400 active volcanoes, Io is the most geologically active object in the Solar System. This extreme geologic activity is the result of tidal heating from friction generated within Io's interior as it is pulled between Jupiter and the other Galilean satellites--Europa, Ganymede and Callisto.
With over 400 active volcanoes, Io is the most geologically active object in the Solar System. This extreme geologic activity is the result of tidal heating from friction generated within Io's interior as it is pulled between Jupiter and the other Galilean satellites--Europa, Ganymede and Callisto.
Europa, is the sixth-closest moon of Jupiter, and the smallest of its four Galilean satellites, but still the sixth-largest moon in the Solar System. Europa was discovered in 1610 by Galileo Galilei and was named after Europa, daughter of the king of Tyre, who became one of Zeus' lovers. Progressively better observations of Europa have occurred over the centuries by Earth-bound telescopes, and by space probe flybys starting in the 1970s.
Slightly smaller than the Moon, Europa is primarily made of silicate rock and has a water-ice crust and probably an iron–nickel core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is striated by cracks and streaks, whereas craters are relatively rare. It has the smoothest surface of any known solid object in the Solar System.
Slightly smaller than the Moon, Europa is primarily made of silicate rock and has a water-ice crust and probably an iron–nickel core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is striated by cracks and streaks, whereas craters are relatively rare. It has the smoothest surface of any known solid object in the Solar System.
Callisto is a moon of the planet Jupiter. It was discovered in 1610 by Galileo Galilei. It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede, and the largest object in the Solar System not to be properly differentiated.
Callisto is composed of approximately equal amounts of rock and ices, with a mean density of about 1.83 g/cm3, the lowest density and surface gravity of Jupiter's major moons. Compounds detected spectroscopically on the surface include water ice, carbon dioxide, silicates, and organic compounds. Investigation by the Galileo spacecraft revealed that Callisto may have a small silicate core and possibly a subsurface ocean of liquid water at depths greater than 100 km.
Callisto is composed of approximately equal amounts of rock and ices, with a mean density of about 1.83 g/cm3, the lowest density and surface gravity of Jupiter's major moons. Compounds detected spectroscopically on the surface include water ice, carbon dioxide, silicates, and organic compounds. Investigation by the Galileo spacecraft revealed that Callisto may have a small silicate core and possibly a subsurface ocean of liquid water at depths greater than 100 km.
Ganymede is the largest moon of Jupiter and in the Solar System, and the only moon known to have a magnetosphere. It is the seventh satellite outward from Jupiter and third of the Galilean moons, the first group of objects discovered orbiting another planet.
Ganymede is composed of approximately equal amounts of silicate rock and water ice. It is a fully differentiated body with an iron-rich, liquid core, and an internal ocean that may contain more water than all of Earth's oceans together.
Ganymede is composed of approximately equal amounts of silicate rock and water ice. It is a fully differentiated body with an iron-rich, liquid core, and an internal ocean that may contain more water than all of Earth's oceans together.