ENCELADUS: SATURN’S REGENERATING ICY MOON

Saturn’s moon Enceladus displays a geology unlike most other worlds in the solar system. Part of the satellite is heavily cratered, suggesting an ancient surface. Other regions are heavily tectonized and have almost no craters, pointing to an extremely young surface. The youngest region is located near the south pole, where active geologic processes are observed in the form of jets emanating water into space. The leading and trailing hemisphere are similarly young, but lack any observed activity, with terrains that are dominated by numerous large (up to 1 km high) ridges. On the Saturnian and Anti-Saturnian hemispheres, craters dominate the landscape but closer examination reveals a complex surface of both ancient and young tectonic features. The most ancient features are a handful of small ridges (10s m high) and troughs. The ancient ridges appear to be cut by the troughs and craters, suggesting the ridges are the most ancient features preserved on Enceladus’s surface. Similarly, the ancient troughs are cut by everything except the ancient ridges, suggesting they are the next most ancient features on Enceladus. However, extending through the ancient cratered terrains are a series of fractures that cut across all other features. These suggest a very recent and perhaps ongoing episode of tectonism. Here we present a global geological history of Enceladus: Beginning with a period of first ridge and then trough formation. That early deformation was followed by a period of cratering. Recently, the moon experienced a period of partial tectonic resurfacing, dominated by ridge formation which removed many of the craters. Lastly, Enceladus experienced an episode of global fracturing, which may be continuing today.