Deimos picture taken on the Viking Mission

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1 2.1n demonstrate an understanding that some planets have satellite systems with a variety of origins and structures (including Mars and Neptune) Mars has two moons which are incredibly small named Phobos (Fear) and Deimos (Terror), the servants of Mars (The Greek God of War). Phobos is only 22 km long along its biggest dimension, whereas Deimos is only 14 km long. Phobos is closest to the planet, closer than any other moon in the Solar System, being just 9,400 km away from the Martian surface. The two moons appear as large lumps of rock and are thought to be captured asteroids, being very similar in structure to Ceres. The Mars Reconnaissance Orbiter took the image of Phobos:- Picture credit : HiRISE, MRO, LPL (University of Arizona), NASA Picture credit : NASA/JPL Deimos picture taken on the Viking Mission

2 All the gas giants have a large number of moons, many of them having diameters bigger than the planet Mercury. By comparison to the gas giants, their moons are tiny. Jupiter : Io The 4 Galilean moons can be seen orbiting Jupiter using binoculars or a small telescope. Io is the innermost moon, being the third largest of the 4 moons. As Io is relatively close to Jupiter, the huge gravitational pull of the planet causes the ground to rise and fall by up to 9 metres on a regular basis. The friction created causes intense heat and gives rise to active sulphur volcanoes. These can shoot out material up to 300 km high, as can be seen in the photograph. The volcanic activity has given rise to a highly coloured pizza-like surface. Picture credit : NASA/JPL-Caltech Io image taken by the Galileo space probe

3 Saturn : Titan Titan is Saturn s largest moon. The photograph was taken by Voyager 2 in Titan is the only moon in the Solar System that has a dense atmosphere, which extends 600 km out from the surface. This atmosphere is 95% nitrogen + methane and other hydrocarbons and creates a pressure x1.5 than the Earth s atmosphere. The view on the surface was taken by the ESA Huygens probe which landed on the surface of Titan in The surface temperature is -180 C. The surface was found to be soft, like wet clay and covered with pebbles. The material on the ground where the probe landed is very complex in nature and the data sent back to Earth is still being analysed. Picture credit : ESA/NASA/JPL/University of Arizona

4 Uranus : Miranda This is the innermost of the larger moons of Uranus. The moon is half rock and half water ice. Initially thought to have been split by an impact and recombined, the latest theory on its bizarre appearance is linked with similar heating as on Io, related to the gravitational pull of Uranus. Constant movements in the rocky material have led to heat caused by friction. This in turn has caused the melting of the ice and allowed it to flow to the surface, covering over some of the rocky surface. This theory needs testing further to be proved beyond doubt. Picture credit : Voyager Project /NASA/JPL Miranda, with the famous chevron mark which can be seen below centre. The crater (Alonso) below this mark is 24 km across. Some of the canyons are thought to be up to 18 km deep.

5 Neptune : Triton Triton is Neptune s largest moon and is thought to be the coldest place in the Solar System at -235 C. The moon s highly inclined and retrograde orbit (opposite to the direction of the planet s rotation) will see it eventually crash into the surface of Neptune. Current theories believe the moon to have been one of a pair in a binary system. As the pair came close to Neptune, only Triton was captured and the moon began its unusual orbit around its new host. The pink colour is caused by frozen nitrogen at the South Pole. The rock and ice surface of nitrogen and methane is broken by ice volcanoes which shoot liquid nitrogen 8 km up above the surface. The complex ridges and valleys are probably caused by freeze/thaw effects. The surface of Triton is relatively new, with few craters. Another of Neptune s moons, Nereid, has the most eccentric (highly elliptical) orbit of any planet or moon in the Solar System. This moon orbits Neptune in the normal direct way and is thought to be a captured asteroid.