English: The picture compares four large impact structures on Jupiter's icy moon, Europa. Clockwise, from top left, are Pwyll, Cilix, Tyre, and Mannann'an. Impact structures with diameters of more than 20 kilometers are rather rare on Europa. Tyre is most unusual. While the effective crater, which is somewhat larger than the prominent large bull's eye feature, is about 40 kilometers (25 miles) across, the entire structure is much larger. The concentric rings display relatively little relief. Some of the smaller craters near Tyre were formed by material ejected by and then redeposited from the impact which formed Tyre. One hypothesis for such characteristics is that the impactor which formed Tyre penetrated through an icy crust into a less brittle layer. While Pwyll, Cilix, and Mannann'an also display shallow crater depths for their size, they more closely resemble similar sized craters on two neighboring moons of Jupiter, Ganymede and Callisto. Perhaps the impactor did not punch through the upper crust during these events. This might have been the case if the impacting body was smaller or weaker than in the case of Tyre or if the crust was thinner at the location of Tyre during the impact event.