Did Noah PETRO really have ANY choice in becoming Geo or Lunar crustal
specialist? Was his path preordained??
Jerry Flaherty
--------------------------------------------------
From: "Darren Garrison" <[email protected]>
Sent: Saturday, March 06, 2010 8:49 AM
To: <[email protected]>
Subject: [meteorite-list] And there's likely a crater in a crater in
thecrater in the crater
http://www.msnbc.msn.com/id/35728750/ns/technology_and_science-space/
Crater-in-a-crater may offer peek at moon guts
Part of the Apollo Basin may expose a portion of the moon's deep crust
A big crater inside a huge crater on the moon could offer a view of the
lunar
innards, scientists now say.
Here's the setup: Shortly after the moon formed, it got whacked, big time.
The
result, an enormous crater called the South Pole-Aitken basin. It's almost
1,500
miles across and more than five miles deep.
The impact punched into the layers of the lunar crust, scattering that
material
across the moon and into space. The tremendous heat of the impact also
melted
part of the floor of the crater, turning it into a sea of molten rock.
Story continues below ?advertisement | your ad here
"This is the biggest, deepest crater on the moon - an abyss that could
engulf
the United States from the East Coast through Texas," exlained Noah Petro
of
NASA's Goddard Space Flight Center.
But wait, there was more.
Asteroid bombardment over billions of years has left the lunar surface
pockmarked with craters of all sizes, and covered with solidified lava,
rubble,
and dust. Glimpses of the original surface, or crust, are rare, and views
into
the deep crust are rarer still.
Now, scientists say a crater on the edge of the South Pole-Aitken basin
may
provide just such a view. Called the Apollo Basin and formed by the later
impact
of a smaller asteroid, it is about 300 miles across.
"It's like going into your basement and digging a deeper hole," Petro
said.
"We believe the central part of the Apollo Basin may expose a portion of
the
moon's lower crust," he said. "If correct, this may be one of just a few
places
on the moon where we have a view into the deep lunar crust, because it's
not
covered by volcanic material as many other such deep areas are. Just as
geologists can reconstruct Earth's history by analyzing a cross-section of
rock
layers exposed by a canyon or a road cut, we can begin to understand the
early
lunar history by studying what's being revealed in Apollo."
Petro presented his research Thursday at the Lunar and Planetary Science
meeting
in Houston. It was done using the moon Mineralogy Mapper (M3), a NASA
instrument
on board India's Chandrayaan-1 lunar-orbiting spacecraft. Analysis of the
light,
or spectra, in images revealed that portions of the interior of Apollo
have a
similar composition to the impact melt in the South Pole-Aitken (SPA)
basin.
As you go deeper into the moon, the crust contains minerals have greater
amounts
of iron, the researchers explained in a statement. When the moon formed,
it was
largely molten. Minerals containing heavier elements, like iron, sank down
toward the core, and minerals with lighter elements, like silicon,
potassium,
and sodium, floated to the top, forming the original lunar crust.
"The asteroid that created the SPA basin probably carved through the crust
and
perhaps into the upper mantle," Petro said. "The impact melt that
solidified to
form the central floor of SPA would have been a mixture of all those
layers. We
expect to see that it has slightly more iron than the bottom of Apollo,
since it
went deeper into the crust. This is what we found with M3. However, we
also see
that this area in Apollo has more iron than the surrounding lunar
highlands,
indicating Apollo has uncovered a layer of the lunar crust between what is
typically seen on the surface and that in the deepest craters like SPA."
The lower crust exposed by Apollo survived the impact that created SPA
probably
because it was on the edge of SPA, several hundred miles from where the
impact
occurred, according to Petro.
Both SPA and Apollo are estimated to be among the oldest lunar craters,
based on
the large number of smaller craters superimposed on top of them. As time
passes,
old craters get covered up with new ones, so a crater count provides a
relative
age; a crater riddled with additional craters is older than one that
appears
relatively clean, with few craters overlying it. As craters form, they
break up
the crust and form a regolith, a layer of broken up rock and dust, like a
soil
on the Earth.
Although the Apollo basin is ancient and covered with regolith (what we
call
dirt on Earth), it still gives a useful view of the lower crust because
the
smaller meteorite impacts that create most of the regolith don't scatter
material very far.
"Calculations of how the regolith forms indicate that at least 50 percent
of the
regolith is locally derived," said Petro. "So although what we're seeing
with M3
has been ground up, it still mostly represents the lower crust."
Earth was bombarded back then, too. But the record of the events have been
folded back into our active planet or weathered away. On the moon, which
is
comparatively dead geologically, the record of scars remains.
"The Apollo and SPA basins give us a window into the earliest history of
the
moon, and the moon gives us a window into the violent youth of Earth,"
Petro
said.
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