The Moons of Saturn

The moons of Saturn are numerous and diverse, ranging from tiny moonlets (a very small bodies orbiting a planet, often as part of a ring) less than 1,000 metres (0.62 miles) across to the enormous Titan, which is larger than the planet Mercury. Saturn has 62 moons with confirmed orbits, 53 of which have names, and only 13 of which have diameters larger than 50 kilometres (31 miles). Saturn has seven moons that are large enough to become spherical, and dense rings with complex orbital motions of their own, making the Saturnian system the most diverse in the Solar System. Particularly notable among Saturn’s moons are Titan, the second largest moon in the Solar System, with an Earth-like atmosphere and a landscape including hydrocarbon lakes and dry river networks, and Enceladus, which emits jets of gas and dust and may harbor liquid water under its south pole region. The Saturnian moon system is very lopsided, with one moon, Titan, comprising more than 96% of the mass in orbit around the planet. The six other oblate moons constitute roughly four percent, while the remaining 54 small moons, together with the rings, comprise only 0.04%. Co-orbitals moons Janus and Epimetheus are called co-orbital moons. They are of roughly equal size, with Janus being slightly larger than Epimetheus. Janus and Epimetheus have orbits with only a few kilometers difference in semi-major axis, close enough that they would collide if they attempted to pass each other. Instead of colliding, however, their gravitational interaction causes them to swap orbits every four years. inner large moons • Mimas is the smallest and least massive of the inner round moons, although its mass is sufficient to alter the orbit of Methone (another moon). It is noticeably ovoid-shaped, having been made shorter at the poles and longer at the equator (by about 20 km) by the effects of Saturn’s gravity. Mimas has a large impact crater one third its diameter situated on the moon’s leading hemisphere called Herschel. The moon has no known past or present geologic activity, and its surface is dominated by impact craters. • Enceladus is one of the smallest moons of Saturn that has spherical shape—only Mimas is smaller. Yet Enceladus is the only of Saturn’s moon, except much larger Titan and possibly Dione that is currently active. The surface of the moon is morphologically diverse (morphological classification is a system used by astronomers to divide galaxies into groups based on their visual appearance); it includes ancient heavily cratered terrain as well as younger smooth areas that contain only few impact craters. Saturn’s moon phoebe Phoebe is the first satellite to be discovered photographically. It is over eight million miles away from Saturn, over four times farther from Saturn than its nearest neighbour, the moon Iapetus. Originally thought to be a captured asteroid (any of numerous small celestial bodies that revolve around the sun, with orbits lying chiefly between Mars and Jupiter and characteristic diameters between a few and several hundred kilometres. Also called minor planet or planetoid), Phoebe was found to contain carbon dioxide, which has never been found on an asteroid. Phoebe is now thought to be either a comet or Kuiper Belt object (an area that extends from the orbit of Neptune out to 4.7 billion miles from the sun). One reason for believing Phoebe to be a comet or Kuiper Belt object is its highly unusual orbit. While most of Saturn’s moons orbit around its equator, the plane of Phoebe’s orbit is 175° from the equator of Saturn. Also, the moon rotates retrograde (Apparently moving backward, and contrary to the succession of the signs, that is, from east to west, as a planet). While most of the moons of Saturn are composed mainly of ice and therefore have relatively high albedos (reflectivity), Phoebe is estimated to be composed of 50% rock and is known to have a very low albedo. The dark colouring is part of the reason that it was first hypothesized that Phoebe was an asteroid. The surface of Phoebe is not only dark but also heavily scarred and cratered, with several substantial craters. Only in 2000, when several smaller new moons were discovered by scientists, was it determined that Phoebe is not the farthest moon from Saturn. calebunda1@yahoo.com