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A Moon Rock's Biography
A study in the 30 July 2004 issue of the journal Science of a new lunar meteorite has revealed that the rock endured three impact events before a fourth that ejected it from the moon.
The European and U.S. authors dated the four impacts, which should allow researchers to refine their global model of the moon's evolution. Meteorite Sayh al Uhaymir 169 is roughly the size of an adult fist (70 x 43 x 40 millimeters) and was found in Oman in 2002.
Edwin Gnos and colleagues have now analyzed the rock's geology and unique chemical composition, which allowed them to pinpoint its point of departure from the moon: the Lalande impact crater. The authors' data offer a picture of the major milestones in the meteorite's life on the moon. Each impact jostled the rock and changed its position.
It was launched into space by the fourth impact approximately 340,000 years ago. Eventually, after orbiting either Earth or the Sun, the meteorite was captured by Earth's gravity field.
A related "Perspective" further discusses these findings.
29 July 2004