 Voyager image of Janus. |
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| JANUS - MOON OF SATURN | ||
| Janus is a Roman god associated with gates and doors. In statues and carvings he is represented as having two faces, looking in opposite directions. Janus was worshipped at important events such as harvest time, births and marriages because he represented change and transition. Janus was discovered by the French astronomer, Audouin Dollfus in 1966. | ||
| Orbit | ||
| Janus is co-orbital (shares an orbit) with Epimetheus. The two orbit Saturn at a distance of about 151,472 kilometres and 151,422 kilometres, their paths separated by just 50 kilometres. When the inner satellite approaches the outer satellite, it gains orbital momentum which raises its orbit while slowing the outer satellite down. This causes the outer satellite to drop into a lower and faster orbit. The satellite formerly on the inner track becomes the outermost. This change-over appears to occur every four years and is thought to have resulted from the break-up of a single larger body. Janus orbits Saturn with a period of 0.695 days, the same time it takes to rotate on its own axis. Janus exhibits synchronous rotation. | ||
 Janus orbiting outside the edge of the A ring. |
 The orbits of Pandora, Janus, Epimetheus, and Mimas. |
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 Voyager image of Janus (centre right) and Saturn's rings. |
 Hubble Space Telescope image of Mimas, Tethys, Janus and Enceladus, clustered at the western side of the edge-on ring system. |
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| Physical properties | ||
| Janus is irregular in shape and measures 196 x 192 x 150 kilometres.Interior | ||
| Surface | ||
| It is similar in appearance to its orbital twin Epimetheus. Both have an albedo of about 0.8 and are very bright. Their largest craters are about 30 kilometres across. They have many smaller craters which are more pristine. These are about 5 kilometres across. The similarities in crater density and size distribution indicate both moons are quite old. | ||
| Interior | ||
| Janus has a density of 650 kg m-3, which is very low indeed. It has one of the lowest recorded densities of any Solar System object. Such a low density implies that Janus is very porous, having a holey or sponge-like structure. | ||
| Magnetic field | ||
| No magnetic field has been detected. | ||
| Atmosphere | ||
| No atmosphere has been detected. | ||
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