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Two years ago we reported evidence that
the moon is shrinking. Now we found

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evidence that the moon is actually being
pulled apart forming features called

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graben.
So the shrinking moon it turns out is

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not shrinking everywhere. Some places the
moon is actually expanding by a little

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bit.  So finding these young graben was a
real surprise because we thought well

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all these lobate scarps are telling us
the moon is shrinking so what are these

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little small graben that are telling us
the moon is pulling apart doing in in

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this picture how does this all fit
together. All that's related to how the

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moon has evolved how the moon has lost
heat over its four-and-a-half billion

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year history. Most of the terrestrial
planets when they formed were very hot

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and they got so hot that they actually
completely melted. When that happens they

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will be in a general state of
contraction because they're still hot on

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the inside and cooling down. And as they
cool they want to shrink. Only the outer

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part of the Moon melted forming what is
called a magma ocean. And in that model

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the balance of stresses or forces that
are acting on the moon would allow us to

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form both these small lobate scarps that
show contraction as well as the small

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graben on that show the moon being pulled
apart. One of the really really exciting

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returns of the Lunar Reconnaissance
Orbiter mission is that we've seen this

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now growing evidence of very young
geologic activity on the moon. Many many

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people have felt that the moon was
pretty much geologically dead. And what

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we're finding is that that's totally
wrong. That the moon appears to be

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geologically active now.

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Music

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