The moon
22 Images

Moons of the solar system

The moon
A view of Earth’s moon taken by the Galileo spacecraft in 1992 on its way to explore Jupiter. (NASA)
Phobos
Phobos, the largest of Mars’ two moons, is a cratered, asteroid-like object. It orbits so close to Mars that in around 100 million years it will probably be shattered by stress caused by relentless tidal forces. (NASA)
Europa
One of Jupiter’s largest moons, Europa is covered in a thick layer of ice which holds a vast, watery ocean underneath. Despite is extremely cold temperature, some astronomers and scientists believe the ocean is capable of harboring life. Europa is roughly the size of Earth’s moon. (NASA)
Europa’s rigid surface
The spots and pits visible on Europa’s icy surface suggest warmer ice is forcing its way up through the frozen shell. Evidence points to a vast, deep ocean of water below the frozen surface. (NASA)
Io
Io, the innermost of Jupiter’s many moons, is one of the most volatile destinations in the solar system. Jupiter’s immense gravitational pull creates extreme geological activity on the satellite, which has more than 400 volcanos. The lava flows from the volcanos create significant surface changes over relatively short periods of time. (NASA)
Ganymede
Ganymede is Jupiter’s largest moon -- and the largest in the solar system. It is covered in impact craters and is believed by some scientists to harbor a subterranean ocean. It is also the only moon in the solar system to have a magnetosphere. (NASA)
Callisto
The heavily cratered Callisto is the third-largest moon in the solar system, with a diameter nearly the same as the planet Mercury. The moon’s orbit around Jupiter is tidally locked, and it shows no signs of plate tectonics. (NASA)
Titan
Saturn’s largest moon, Titan, is the only satellite in the solar system to have a dense atmosphere, comprised mostly of nitrogen. Titan’s planetlike characteristics have made it one of the most intriguing moons in the solar system and a target for research by astronomers and scientists. In 2005, the Cassini-Huygens spacecraft arrived in the Saturn system to study the ringed planet and its moons. (NASA)
Titan
Titan’s hazy, orange-colored atmosphere is believed to be the result of the breaking up of methane by ultraviolet light from the sun. (European Space Agency)
Surface of Titan
The European Space Agency’s Huygens probe landed on the surface of Titan in 2006, transmitting this image back to Earth. The dense atmosphere on Titan creates an almost constant fog-like state during the moon’s daylight periods. The satellite’s rocky surface is interrupted by lakes of liquid methane. Scientists say there are enough organic building blocks on the moon to possibly start or support life. (European Space Agency)
Tethys
Saturn’s moon Tethys, containing a combination of smooth plains and heavily cratered areas, formed in the same sub-nebula that created Saturn and all of its biggest moons. Craters dominate the satellite’s surface, with the huge, shallow crater named Odysseus dwarfing the others. (NASA)
Mimas
With a surface area roughly the size of Spain, Mimas isn’t one of Saturn’s biggest moons, but the distinguishing crater on its surface makes it one of the solar system’s more recognizable satellites. The crater -- named Herschel for its discoverer William Herschel -- has led some to say it resembles the Death Star of “Star Wars” fame. (NASA)
Enceladus
Enceladus, Saturn’s sixth-largest moon, is believed to have a vast ocean of liquid water under its surface. Its icy surface helps it reflect nearly all of the sunlight it receives, giving it a bright appearance. Cryovolcanoes near the moon’s south pole shoot jets of ice particles into space, many of which are then absorbed into Saturn’s rings by the planet’s immense gravity. (NASA)
Dione
Composed mostly of water ice, Saturn’s moon Dione features a heavily cratered terrain in its leading hemisphere. Its trailing hemisphere contains a network of bright ice cliffs created by tectonic movement. (NASA)
Rhea
Rhea, Saturn’s second-largest moon, has an icy, cratered surface that is similar to Dione’s. Its low density suggests that it is mostly composed of water ice. (NASA)
Iapetus
Distinguished by the two-tone coloration of its surface, Iapetus is one of 62 known moons orbiting Saturn. In addition to its odd coloration, the moon also has a massive crater named Turgis, which measures more than 360 miles in diameter. A long ridge also runs halfway around its surface at its equator. (NASA)
Oberon
The outermost moon of Uranus, Oberon consists of equal parts ice and rock. Its slightly red color is believed to be caused by numerous asteroid and comet impacts. Like many of Uranus’ moons, it has an extreme seasonal cycle due to its equatorial plane orbit and Uranus’ side orbit. As a result, its poles spend 42 years in daylight followed by 42 years in darkness. (NASA)
Titania
Composed mostly of ice and rock, Titania is the largest moon in the Uranian system. The moon’s surface is relatively dark and red in color and is less cratered than other moons orbiting Uranus. Water ice absorption bands wrap around the moon’s leading hemisphere, but a crater known as Gertrude (upper right) is perhaps its most noticeable feature from the side of the moon photographed by Voyager 2 in 1986. (NASA)
Miranda
The innermost of the larger Uranian moons, Miranda has a unique variety of terrain, leading some to suggest that it has been fractured multiple times during its evolution. This composite image of Miranda shows numerous ridges and valleys and canyons up to 12 miles deep.  (NASA)
Ariel
The fourth-largest moon of Uranus, Ariel has an extreme seasonal cycle since it orbits and rotates in the planet’s equatorial plane. Much of the surface is composed of heavily cratered terrain that is laced by fault-bounded valleys. (NASA)
Triton
Triton is the largest moon of Neptune and is one of the few bodies in the solar system to have a nitrogen-dominated atmosphere. Triton’s cold temperature makes it the only satellite in the solar system known to have a surface made primarily of nitrogen ice. (NASA)
Charon
Orbiting the dwarf planet of Pluto is Charon (bright light lower right), which was discovered in 1978. Since then, two new moons -- Nix and Hydra -- have also been discovered orbiting Pluto. More detailed photographs of Pluto and its satellites are expected to be relayed back to Earth in 2015 when NASA’s New Horizons spacecraft arrives to study the dwarf planet. (NASA)
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