Lunar Reconnaissance Orbiter Science Targeting MeetingTempe, Arizona
June 2009
Dr. Barbara A. Cohen
NASA Marshall Space Flight Center
One of the important outstanding goals of lunar science is understanding the bombardment history of the Moon and calibrating the impact flux curve for extrapolation to the Earth and other terrestrial planets. The "terminal lunar cataclysm," a brief but intense period of bombardment about 3.9 billion years ago, is of particular scientific interest.
Radiometric dating of lunar impact-melt rocks forms the backbone of the lunar cataclysm hypothesis. A histogram of precise age determinations of impact-melt rocks shows the characteristics of the classic formulation of the lunar cataclysm hypothesis: a sharp peak at 3.9 billion years, a steep decline after 3.9 billion years and perhaps only 20-200 million year long, and few rocks of impact origin prior to 4 billion years.
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