[meteorite-list] Proposed Lunar Mission Could Shed Light On How The Moon Was Formed

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:27:46 2004
Message-ID: <200311100244.SAA19021_at_zagami.jpl.nasa.gov>

http://www.stltoday.com/stltoday/news/stories.nsf/News/47A57F9826F24CBE86256DD8001917C6

Mission could shed some light on how the moon was formed
By ELI KINTISCH
St. Louis Post-Dispatch
November 7, 2003

Lunar craters have given us tantalizing bits of information.
Scientists hope a mission proposed for 2009 can tell us
more.

Looking forward to the lunar eclipse tonight? The real show
was 4 billion years ago.

Back then, volleys of meteoroids, many dozens of miles
wide, bombarded the young moon. The energy blasted holes
miles deep into the lunar landscape and flung boulders into
space. Some impacts shook the entire moon with their force,
said lunar geochemist Randy Korotev of Washington
University.

"I often think I wish I could have been there to see it," said
Korotev. "But I don't know where I'd stand."

Lunar craters are some of our best clues about the Earth's
first half billion years. Our planet took a similar beating
back then, but the evidence has been erased by plate
tectonics and weather. Missions to the moon have
delivered clues about the era, but debate rages over how
the nascent days of the solar system looked. Now three
Washington University scientists are helping propose an
unmanned mission in 2009 to the dark side of the moon, as
it's known colloquially, to learn more.

Craters on the near side of the moon, where the Apollo
astronauts explored, have their own secrets. Among other
things, analysis of moon rocks has suggested that the moon
formed in less than a million years, and led scientists to
theorize the existence of a hot moon sea.

One giant crater, known as Imbrium, is especially
enigmatic. That crater was formed by a rocky meteoroid
about 40 miles across, said Washington University chemist
Larry A. Haskin. The meteoroid blasted rock out from more
than 4 miles deep inside when it hit.

In 1998 a NASA spacecraft called the Lunar Prospector
scanned the moon's surface and found relatively high
amounts of a trace element called thorium concentrated in
rocks in the general area of Imbrium.

Moon rocks brought back from that area by Apollo
astronauts had shown high concentrations of thorium, so
scientists had mistakenly theorized that these elements
were evenly distributed in a layer deep within the moon. As
meteoroids punched into the moon's interior, the theory
went, the thorium was blasted out onto the surface.

Yet the moon surface is pockmarked with craters. If the
thorium was in fact evenly distributed, Lunar Prospector
would have detected it all over the moon.

The fact that the thorium was found on only one side raises
intriguing questions. Were "tides," as Haskin called them,
pulling the thorium on a sea of melted rock toward the
Earth?

"Nobody knows yet," said Haskin, who has been studying
the Imbrium crater for years with Korotev and Washington
University planetary geologist Bradley L. Jolliff. The three
are now trying to answer another question: Was the
Imbrium impact simply the last of a long line of impacts, or
was it part of a sustained barrage that scientists call the
"cataclysm"?

The answer may lie on the moon's far side. NASA recently
determined that a mission to take rock samples from a
crater there would be one of four candidates for a 2009
unmanned effort. The trio here is helping develop a proposal
for the endeavor.

If rocks from that side of the moon are the same age as the
samples taken near Imbrium - roughly 3.9 billion years old
- that could mean the cataclysm was real.

And that, in turn, would rewrite the early history of our
solar system.
Received on Sun 09 Nov 2003 09:44:46 PM PST