The collection of rocks that the Apollo astronauts brought back from the moon carried with it a riddle that has puzzled scientists since the early 1970s: What produced the magnetization found in many of those rocks? The longstanding puzzle has now been solved by researchers, who carried out the most detailed analysis ever of the oldest pristine rock from the Apollo collection. Magnetic traces recorded in the rock provide strong evidence that 4.2 billion years ago the moon had a liquid core. (source: web.mit.edu)
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