Moons of the Giant Planets Europa

Callisto is the outermost of Galilean moons at a distance of 1 Callisto is the outermost of Galilean moons at a distance of 1.2 million miles. It is in synchronous revolution around Jupiter every 17 days. The moon has a heavily cratered surface that has seen little change over the last 4.4 billion years. CALLISTO

Callisto froze solid before the process of differentiation occurred Callisto froze solid before the process of differentiation occurred. It is a geologically dead world. CALLISTO

Closeup of Callisto

GANYMEDE Ganymede is the largest moon in the Solar System. Parts of its surface are very old like Callisto but others are relatively young, perhaps a billion years old. Ganymede may have a rocky, metallic core. Tidal forces may occasionally heat the interior and cause water to erupt and resurface portions of the moon. GANYMEDE

Closeup of Ganymede

Europa is predominantly a rocky world with an ice-covered surface that is crisscrossed with cracks and low ridges. Few craters are evident. The ice appears to be the frozen surface of a great water ocean that has broken up and refrozen many times. EUROPA

Tidal forces may generate enough heat to keep water in the liquid state not too far beneath the surface layer of ice. EUROPA

Closeup of Europa

IO is a close twin our Moon with about the same size and density. Io has active volcanoes on its surface. Volcanoes emit hot rocky lava, sulfur and sulfur dioxide. The sulfur and sulfur dioxide recondense in the cold and snow down upon Io’s surface. IO

Io is constantly resurfacing itself.

Closeup of Io

Moons of Saturn 19 Moons and Massive Ring System Titan is most significant satellite and the only moon with a significant atmosphere Ring material size of ping-pong, tennis and basketballs.

Saturn’s Titan is about the size of Jupiter’s Ganymede and is about half ice and half rock. It is the only moon to have a substantial atmosphere. The atmospheric surface pressure is 1.6 times that of Earth. Io

Titan’s atmosphere is composed mostly of methane Titan’s atmosphere is composed mostly of methane. Nitrogen and hydrocarbon compounds are also present. Methane clouds composed of shroud the surface. The surface is probably covered with methane ice and perhaps methane oceans. Io

Tethys Tethys's icy surface is heavily cratered and contains cracks caused by faults in the ice. There is one enormous trench on Tethys about 65 kilometers wide and extending from above the center to the extreme left. It covers three-fourths of Tethys' circumference. The fissure is about the size scientists would predict if Tethys were once fluid and its crust hardened before the interior. The canyon has been named Ithaca Chasma.

Enceladus: Enceladus is one of the innermost moons of Saturn. Enceladus reflects almost 100 percent of the sunlight that strikes it. The uncratered regions are geologically young and suggest that Enceladus has experienced a period of relatively recent internal melting. The rims of several craters near the lower center of the picture have been flooded by the smooth terrain.

Dione Dione was discovered in 1684. It is an icy body with a density of 1.43 gm/cm3, which makes it the densest moon of Saturn other than Titan. Dione is probably composed of a rocky core making up one-third of the moon's mass, with the rest water-ice. Dione's icy surface includes heavily cratered terrain, moderately cratered plains, lightly cratered plains, and wispy material.

Mimas One of the craters, named Herschel, is surprisingly large in comparison to the size of the moon. The crater is 130 kilometers wide, one-third the diameter of Mimas. Herschel is 10 kilometers deep, with a central mountain almost as high as Mount Everest on Earth. This central mountain rises 6 kilometers above the crater floor. This impact probably came close to disintegrating the moon.

Moons of Uranus 18 Moons and 11 Dark Rings Miranda – A Moon that may have broken up and then reassembled. Moons of Neptune 8 Moons Triton – A large satellite in retrograde orbit

Miranda Its surface is unlike anything in the Solar System with features that are jumbled together in a haphazard fashion. Miranda consists of huge fault canyons as deep as 20 kilometers terraced layers and a mixture of old and young surfaces.

It is believed that Miranda may have been shattered as many as five times during its evolution. After each shattering the moon would have reassembled from the remains of its former self with portions of the core exposed and portions of the surface buried.

Cutting across the ridges and valleys are many faults Cutting across the ridges and valleys are many faults. The largest fault scarp, or cliff, is seen below and right of center. The fault may be 5 km (3 mi) high, or higher than the walls of the Grand Canyon on Earth.

Miranda

Io Triton is the largest moon of Neptune. It has the coldest temperature of any object unmanned spacecraft have visited – 35-40 degrees above Absolute Zero. Triton is so cold that N and CH4 are frozen on its surface. The moon is 75% rock and 25% water ice. Io