Ray crater
A ray crater has bright streaks of ejecta radiating outwards, a sign that it is relatively young.
A ray crater is surrounded by bright streaks, called rays, that spread outwards like spokes of a wheel. The rays are made of material thrown out during the impact, including fine debris and many small secondary craters made by falling blocks.
On the Moon, the crater Tycho, about 85 kilometres across, has rays that stretch more than 1,500 kilometres and are easily seen with binoculars at full Moon. Copernicus and Kepler also have prominent rays. Rays are bright because they expose fresh, unweathered material.
Over time, space weathering by the solar wind and micrometeorites darkens rays until they fade into the surrounding surface. So rays mark relatively young craters, perhaps less than about a billion years old. Tycho is thought to be about 100 million years old, based on samples possibly related to it collected by Apollo 17. Ray craters also exist on Mercury and on some icy moons.
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Level: Explorer Ages 10 and up