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NASA's twin GRAIL probes may find remnants of moon's lost sibling

December 31, 2011 - Washington

Two identical NASA space probes are due to arrive at the moon on New Year's Eve and New Year's Day to find if the Earth's companion holds the wrecked body of a lost sibling body.

The twin GRAIL probes will determine what lies beneath the lunar crust by measuring the moon's gravitational field, Discovery News reported.

The spacecraft will chase each other 34 miles above the moon's surface, speeding up and slowing down in response to gravitational forces.

By measuring the changing distance between the two, scientists can determine the moon's gravity and then model what is inside.

Evidence of the crash, if it occurred, should be buried inside the moon, in the form of remnant radioactive materials, like uranium and thorium, which would have been heated in the smash-up.

According to a recently published paper, scientists suspect a second moon once circled Earth in the same orbit and at roughly the same speed as our moon. It eventually bumped into its companion, but instead of causing an impact crater, the second moon stuck and made a mountain.

That feature today would be the lunar highlands located on the side of the moon that permanently faces away from Earth.

"One prediction of this model is that the whole exterior of the moon was once molten, and it started to cool off-actually cooled from the outside in-so you were left with a molten channel in the base of the moon's crust," said planetary scientist Maria Zuber, with the Massachusetts Institute of Technology.

Simulations show that when the second moon hit our moon the molten material was pushed around to the near side, traces of which should remain today.

"We're looking for layering in the lower crust," added Zuber, who is the lead researcher on NASA's Gravity Gravity Recovery and Interior Laboratory, or GRAIL, mission.


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