Hugh Pickens writes writes: "AFP reports that new images from a pair of spacecraft that are orbiting the Moon and measuring its gravitational field point to a violent past in which it was battered by comets and asteroids during its first billion years. "It was known that planets were battered by impacts, but nobody had envisioned that the (Moon's) crust was so beaten up," says Maria Zuber, the MIT scientist leading the mission. "This is a really big surprise, and is going to cause a lot of people to think about what this means for planetary evolution." As the pair of spacecraft named Ebb and Flow flew over areas of greater and lesser gravity, caused both by visible features such as mountains and craters and by masses hidden beneath the lunar surface, they moved slightly toward and away from each other. An instrument aboard each spacecraft measured the changes in their relative velocity very precisely, and scientists translated this information into a high-resolution map of the Moon's gravitational field. Unlike the Earth's crust, which is repeatedly recycled through the process of plate tectonics, the Moon's hard crust dates back billions of years, offering clues to the formation of the solar system, including Earth. Around 98 percent of the crust is deeply fragmented, porous material, the result, scientists say, of very early, massive impacts. Scientists say the beating was far more extensive than previously thought. "This is interesting for the Moon," says Zuber. "But what it also means is that every other planet was being bombarded like this.""
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