Findings of the Tandem satellites probe the Moon's interior
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The first is that the Moon’s crust seems to be thinner than thought. When lunar geologists first estimated the thickness of the Moon’s crust, using data from seismometers placed by the Apollo astronauts, they concluded that it was around 60 kilometres thick. Subsequent re-analyses of those data brought the estimate down to around 45 kilometres. Now, GRAIL’s results suggest that the crust’s average thickness is only 30 kilometres, says Zuber.
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The second finding is that there is a high correlation between variations in the Moon’s gravitational field and its topography. “This, to me, is one of the most surprising things we found,” says Zuber. The result suggests that the gravitational field of the Moon is dominated by its deep craters rather than the structure of its interior. This relationship between topography and gravity was closer for the Moon than for other terrestrial bodies such as Mars, Venus and Earth, Zuber says. “It actually makes you wonder how well we understand the other terrestrial planets.”
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Third, Zuber reported that GRAIL has not been able to confirm some of the larger and older impact basins hypothesized to exist on the Moon’s surface. Lunar scientists examining the Moon’s surface have tried to unravel the history of asteroid impacts — which would illuminate the evolution of not only the Moon but also other bodies of the inner Solar System — by defining areas where large impact basins might underlie more visible and obvious craters. But GRAIL hasn’t found many of the hypothetical basins, Zuber says.
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http://www.nature.com/news/tandem-satellites-probe-the-moon-s-interior-1.11419