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With a thin crust, the Moon’s origin is entwined with Earth’s

NASA/ARC/MIT

NASA has unveiled the most precise map yet of the Moon’s gravity field — the most detailed map of any body in the Solar System, including Earth (pictured).

Analysis of the gravity data shows that the Moon’s crust is between 34-43 kilometres thick — about 20 kilometres thinner than thought during the Apollo era.

And with a crustal bulk density also lower than previously thought, the Moon can have the same basic composition as Earth. That sits well with recent theories about the Moon-forming impact 4.5 billion years ago that suggest a common compositional origin for the Moon and Earth.

The gravity maps have also revealed dikes — thin, linear lines of solidified magma — along with circular mass concentrations that are the ghostly signatures of ancient impact basins.

The results were announced today by the GRAIL team, at a meeting of the American Geophysical Union in San Francisco, in conjunction with a paper published in Science.

The data were obtained by two twin spacecraft, nicknamed Ebb and Flow, that have chased each other around the Moon since 1 January 2012, exchanging radio signals. Variations in their relative positions are used to calculate the minuscule accelerations and decelerations caused by lumpiness in the Moon’s gravity field.

The team has not yet published the more complicated analysis needed to illuminate the detailed inner structure of the Moon, including its core. The mission, already in an extended phase where the probes are orbiting 23 kilometres above the surface, will end on 17 December with a crash.

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