Square Craters
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Square Craters

October 27, 2009
Craters generally tend to be round, but this image shows some craters that are more square than round. The likely reason for this is that Eros had some fractures (known as structural features) at its surface that were present before the impact events that formed the craters. These fractures can be seen in the lower part of the top crater. When the impacts that formed these craters occurred, the resulting crater cavities were influenced by the fractures. The result is that the crater rims that run parallel to the fractures are straighter than craters located in nonfractured areas. Geologists call this kind of effect on the craters "structural control", and a similar occurrence can be seen on Earth at Arizona's Barringer Meteor crater, which also has a slightly squared-off shape to its rim. Note also the boulder perched just beyond the right hand rim of the top crater that looks like a bright speck in the image. The shape of the boulder can be seen by its shadow, which is cast onto the crater floor. The shadow shows that the boulder is diamond shaped, and it appears to be standing on one tip. This image was taken on April 26, 2000, when NEAR Shoemaker was 50 kilometers above the surface.

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