Saturn is the second largest of the planets, and has prominent, beautiful rings, first seen by Galileo Galilei in the early 1600s, but he was so surprised he drew them as 'ears'.
Saturn has been visited by a number of probes, and yet we are still discovering fascinating things about the planet, its ring system and many moons.
First visited by Pioneer XI in 1979, it was revisited by Voyager 1 in 1980, and Voyager 2 in 1981. The latest probe was Cassini in 2009, which entered Saturnalian orbit.
Saturn has a tilt similar to Earth's, causing seasonal variations in temperature as the solar radiation varies angle of incidence and intensity. This temperature variation affects the rings as well, causing changes which Cassini was able to observe, revealing vital information about their structure and composition.
The rings temperature was measured by Cassini's Composite Infrared Spectrometer. Currently, it is believed that the behaviour of Ring A (the outermost of the large rings), which did not fit computer models, was due to the composition of the particles. These are estimated to be about 1, in diameter, and consist of solid ice, with a thin costing of regolith. Their clulstered distribution is still puzzling space scientists. Perhaps a 'shepherd moon' was responsible - but where is it now?
Saturn has a complex system of rings, as well more than 62 satellites. These are stunning in their diversity and activity.
Enceladus was given a closeup examination by NASA's Cassini probe in 2008. Enceladus is geologically active, evidenced by visible jets. The icy moon's surface is covered by fractures, folds and ridges, as the small world's tectonic plates jostle around. This is usually only observed with larger bodies.
Image Credit: NASA/JPL/Space Science Institute
Cassini is an international project, combining the resources of NASA, the ESA, and the Italian Space Agency. A great deal of research and computer modelling of the jets observed in earlier missions, including comparisons to similar eruptions on Earth, where magma pours out of deep fractures, to produce 'curtains of fire', led to the discovery that the jets on Enceladus are not what they seem.
Due to the folds in the surface of the moon, curtains of eruptions can appear as individual jets, but Cassini has revealed this to be an optical illusion.
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