Saturn. Photo: NASA
Read The Saturn's ice rings and inner moons may have been created as a result of the same cosmic event. Astrophysicist Robin Canup of the Planetary Science Directorate of the Southwest Research Institute in Boulder has compiled this thesis based on calculations. A meteorite surrounded by a layer of ice could have been peeled off by the tidal forces near the planet before it crashed into Saturn. From the detached ice chunks, extremely massive rings would have formed, which gradually expanded. In the margins, the inner moons of the planet could eventually have formed, reports Canup. Because of its mysterious rings, Saturn has been fascinating humanity for hundreds of years. Even today, because while a lot is known about the second largest planet of our solar system, but especially on the history of origin is still much speculation. As early as the 19th century, Édouard Albert Roche, astronomer, suggested that a Saturn moon had come so close to the planet that it was broken by the tidal forces and the rings formed from the material. The distance to Saturn, from which such forces can act, is called today according to Roche boundary. Another hypothesis suggests a collision of a meteorite with a moon as a source of material.

Such assumptions, however, contradict a fact that make the Saturn rings exception: they consist of 90 to 95 percent of frozen water. Other celestial bodies are usually composed of at least half of silicates and metals - accordingly, the Saturn rings and the also extremely water-rich inner moons should have a higher proportion of these materials. The hypothesis of Robin Canup provides an explanation for all these objections: it is based on a Saturn companion the size of the Saturn moon Titan, which consisted in the core of silicates and iron, but around a lighter coat of ice carried. When crossing the Roche border, the tidal forces would have shaken and dragged on this layer of ice to such an extent that it was gradually rubbed off and the chunks of ice were distributed in a ring around Saturn. The heavy core, however, was attracted further by the planet and finally crashed into it.

According to the model, the ice rings initially had a good thousand times more mass than today. But after Canup's thesis, they subsequently expanded and lost material at the edges. This evolution may have been further assisted by meteorite collisions around the rings: it could have simultaneously ejected material from the rings while silicates and metals mingled into the rings. From the material drifting away from the rings, the inner moons could finally have formed like Tethys. Evidence for Canup's assumptions may soon be provided by the Cassini spacecraft, which is due to close at the end of its mission to determine the current mass and "fouling" of the Saturn rings before it will burn up in 2017 in the Saturnian atmosphere. If the measurement results match the mass calculated by Canup, this would be a valuable support of the hypothesis. The model could also help understand the formation of lunar and ring systems of other large planets.

Robin Canup (Southwest Research Institute, Boulder): Nature, Vol. 468, No. 7326, p. 943, doi: 10.1038 / nature09661 dapd / Mascha Schacht advertisement


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