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How Old Are the Grooves
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How Old Are the Grooves?

October 26, 2009
Geologists use rules for determining the relative ages of features. One rule says a feature on top of something else is younger than the feature under it. The other rule says one feature is younger than another feature it cuts across. This image of Eros from NEAR Shoemaker, taken June 29, 2000, from an orbital altitude of 51 kilometers (32 miles), shows the kinds of relationships that help scientists determine the age of the asteroid's grooves. The grooves shown here cut across the oldest, must subdued craters and are therefore younger. However, the smaller, younger craters formed on top of the grooves, making the grooves older than those craters. In other words, the grooves in this picture formed part way during the evolution of this region of Eros.