Gravity map shows moon is battered

Twin Nasa probes orbiting the moon have generated the highest-ever resolution gravity field map of any celestial body, showing a record of billions of years of battering of the lunar surface.

The gravity field map reveals an abundance of features never before seen in detail, such as tectonic structures, volcanic landforms, basin rings, crater central peaks, and numerous simple, bowl-shaped craters.

Data also show the moon’s gravity field is unlike that of any terrestrial planet in our solar system, Nasa said.

The new map, created by the Gravity Recovery and Interior Laboratory (GRAIL) mission, is allowing scientists to learn about the moon’s internal structure and composition in unprecedented detail.

Data from the two washing machine-sized spacecraft also will provide a better understanding of how earth and other rocky planets in the solar system formed and evolved.

“What this map tells us is that more than any other celestial body we know of, the moon wears its gravity field on its sleeve,” said GRAIL principal investigator Maria Zuber of the Massachusetts Institute of Technology in Cambridge.

According to Zuber, the moon’s gravity field preserves the record of impact bombardment that characterised all terrestrial planetary bodies and reveals evidence for fracturing of the interior extending to the deep crust and possibly the mantle. This impact record is preserved, and now precisely measured, on the moon.

“With our new crustal bulk density determination, we find that the average thickness of the moon’s crust is between 21 and 27 miles (34 and 43 kilometres), which is about 6 to 12 miles (10 to 20 kilometres) thinner than previously thought.” said GRAIL co-investigator Mark Wieczorek of the Institut de Physique du Globe de Paris.

“With this crustal thickness, the bulk composition of the moon is similar to that of earth. This supports models where the moon is derived from earth materials that were ejected during a giant impact event early in solar system history,” Wieczorek said.

The probes revealed the bulk density of the Moon’s highland crust is substantially lower than generally assumed.

“This data revealed a population of long, linear, gravity anomalies, with lengths of hundreds of kilometres, crisscrossing the surface,” researchers said.

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