Two years ago we reported evidence that the moon is shrinking. Now we found
evidence that the moon is actually being pulled apart forming features called
graben. So the shrinking moon it turns out is
not shrinking everywhere. Some places the moon is actually expanding by a little
bit. So finding these young graben was a real surprise because we thought well
all these lobate scarps are telling us the moon is shrinking so what are these
little small graben that are telling us the moon is pulling apart doing in in
this picture how does this all fit together. All that's related to how the
moon has evolved how the moon has lost heat over its four-and-a-half billion
year history. Most of the terrestrial planets when they formed were very hot
and they got so hot that they actually completely melted. When that happens they
will be in a general state of contraction because they're still hot on
the inside and cooling down. And as they cool they want to shrink. Only the outer
part of the Moon melted forming what is called a magma ocean. And in that model
the balance of stresses or forces that are acting on the moon would allow us to
form both these small lobate scarps that show contraction as well as the small
graben on that show the moon being pulled apart. One of the really really exciting
returns of the Lunar Reconnaissance Orbiter mission is that we've seen this
now growing evidence of very young geologic activity on the moon. Many many
people have felt that the moon was pretty much geologically dead. And what
we're finding is that that's totally wrong. That the moon appears to be
geologically active now.
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