Enceladus

Enceladus is one of Saturn’s moons. It was discovered in 1789 by the German-born British astronomer William Herschel.

Enceladus is the sixth largest of Saturn’s moon and the brightest object in the Solar System. It reflects almost 100 % of the sunlight it receives. Saturn has 62 moons with definite orbits, 53 of which have names. 24 of these are regular satellites that orbit Saturn with only small inclinations to the planet’s equatorial plane. 37 of the remaining 38 are irregular satellites that orbit at high inclinations and a much greater distance from Saturn. These are probably either minor planets captured by Saturn or debris from their break-up during the process. The final irregular satellite is unclear.

Saturn’s moons are named after the Titans and Titanesses, who were the brothers and sisters of the Roman god. When these names had all been used, other names were taken from additional characters in Greek or Roman mythology or from the mythologies of other cultures. The irregular satellites are named after figures from Inuit, Gallic and Norse mythology. Enceladus is named after one of the Gigantes, the giant sons of Gaia, who was the mother of all the heavenly gods. Enceladus had serpent-like limbs, was disabled by a spear thrown by Athena, the goddess of war and heroes and buried under Mount Etna in Sicily. The name was suggested in 1847 by William Herschel’s son.

The composition of Enceladus appears to be a silicate and iron-rich core with a mantle of water and ice. There is pure ice on its surface and there could be liquid water beneath its southern pole. Its surface features include impact craters with domed floors modified by fractures and ridges. There are folded ridges indicating compression and shear forces. Linear grooves and fissures on the surface could be formed by extensional forces due to diapirs, the upwelling of material from the interior of the moon.

Scientists believe the moon is still geologically active and that it has a crust that is just 100 million years old. There are smooth plains formed by water flowing from inside the moon or by cryovolcanism – water ice and ammonia volcanoes. The tectonism may have reoriented Enceladus around its polar axis.

Plumes of icy material, or methane hydrates, resembling geysers rise from its surface. There is a substantial atmospheric plume that is mostly water together with carbon dioxide, carbon monoxide, nitrogen, methane and trace amounts of acetylene, propane and ammonia. Winds appear to have blown dark sand across the surface of the moon.

Enceladus orbits in the densest part of Saturn’s E ring. It takes 1.38 Earth days to orbit Saturn. Along with Saturn and its other moons, it takes 29.4 Earth years to orbit the sun.
Spacecraft missions Voyager 1 and 2 took the first photographs of Enceladus. The Cassini mission to Saturn provided detailed images. Radar imagery at 480 km above Enceladus had a resolution of 1.5 km.