New study explains formation of mysterious moon ‘bulge’

Friday, November 12, 2010

WASHINGTON - A new study has suggested that the bulge of elevated topography on the far side of the moon could be the result of tidal forces acting early in the moon’s history when its solid outer crust floated on an ocean of liquid rock.

Ian Garrick-Bethell, of the University of California, found that the shape of the moon’s bulge could be described by a surprisingly simple mathematical function.

“What’s interesting is that the form of the mathematical function implies that tides had something to do with the formation of that terrain,” said Garrick-Bethell.

The paper described a process for formation of the lunar highlands that involves tidal heating of the moon’s crust about 4.4 billion years ago. At that time, not long after the moon’s formation, the crust was decoupled from the mantle below it by an intervening ocean of magma.

As a result, the gravitational pull of the Earth caused tidal flexing and heating of the crust. At the Polar Regions, where the flexing and heating was greatest, the crust became thinner, while the thickest crust would have formed in the regions in line with the Earth.

This process still does not explain why the bulge is now found only on the far side of the moon.

“You would expect to see a bulge on both sides, because tides have a symmetrical effect. It may be that volcanic activity or other geological processes over the past 4.4 billion years have changed the expression of the bulge on the nearside,” said Garrick-Bethell.

A map of crustal thickness based on the gravity data showed that an especially thick region of the moon’s crust underlies the lunar far side highlands.

The mathematical function that described the shape of the moon’s bulge can account for about one-fourth of the moon’s shape, said Garrick-Bethell.

The new findings were published in the journal Science. (ANI)

Filed under: Science and Technology

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