[meteorite-list] FW: Moon May Hold Earth's Ancient Secrets

From: Robert Verish <bolidechaser_at_meteoritecentral.com>
Date: Wed Aug 3 17:18:15 2005
Message-ID: <20050803211807.82580.qmail_at_web51703.mail.yahoo.com>

http://www.space.com/scienceastronomy/moon_earth_020723.html

  Moon Holds Earth's Ancient Secrets

By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
23 July 2002

Tons of rocks and dust long ago blasted from Earth by
asteroid impacts lay on the Moon's surface and could
hold secrets to our home planet's early history and
the origin of life.

John Armstrong sees the Moon as Earth's attic, and he
figures we should go back and fetch some of the
valuable goods stored there. The information is not
available anywhere else, he and other astronomers
agree.

Armstrong, of the University of Washington in Seattle,
led a new study that concludes the Moon ought to be
littered with terrestrial debris -- some 11,000 pounds
within a few inches of the surface of every square
lunar mile. He told SPACE.com that retrieving some of
it would be the quickest and least expensive way to
learn more about the solar system.

"We are talking about finding material from the very
early Earth," Armstrong explained. "Samples of the
Earth 3.9 to 4.0 billion years ago could tell us a lot
about the state of the early atmosphere, what the
crust and surface were like, and possibly even when
life began to evolve."

Images:

  A close-up view of Apollo 15 lunar sample no. 15415
in the Lunar Receiving Laboratory (LRL):

<http://www.space.com/images/moon_sample_020723_02,0.jpg>
 
  Astronauts David R. Scott, right, commander of the
Apollo 15 mission, gets a close look at the sample
referred to as the "genesis rock" in the Lunar
Receiving Laboratory. Scientist-Astronaut Joseph P.
Allen, left, looks on:

<http://www.space.com/images/moon_rock_020723_02.jpg>

There might also be Venusian rocks on the Moon, say
Armstrong and his colleagues, Llyd Wells of the
University of Washington and Iowa State University's
Guillermo Gonzalez. No rock from Venus has ever been
found, nor is it likely that any will ever be
retrieved from its toasty surface. Gathering one up
would likely reveal a wealth of information about
Venus, astronomers say.

A paper detailing the study will be published later
this year in the journal Icarus.

Late Heavy Bombardment

No one has set foot on the Moon since 1972, the end of
an era of exploration in which Apollo astronauts
brought back 842 pounds (382 kilograms) of material
from the lunar surface. Among the more important
things learned from the lunar dust and rock is that
unlike here on Earth, the stuff on the surface of the
Moon is incredibly old, a record of what was going on
in this neck of the solar system some 4 billion years
ago, just a few hundred million years after the solar
system formed.

Earth's surface is continually recycled, folded deep
inside the planet by the same forces that generate
earthquakes and volcanoes. The Moon, on the other
hand, has almost none of this tectonic activity.

Scientists already knew that rocks from Mars have been
blasted into space and ended up on Earth. They have
found some.

However, few researchers have seriously looked into
the same scenario for terrestrial rock being booted to
the Moon. Armstrong and his colleagues realized that
this transfer of material should have occurred at a
frenzied pace up until about 3.8 billion years ago,
when a period called the Late Heavy Bombardment is
thought to have ended. No material of this sort has
ever been identified, however, and in fact the extent
and timing of the bombardment itself is not known with
certainty.

The bulk of terrestrial rock that's been shot to the
Moon would likely be pebble-sized or dust, having been
pulverized by the initial impact. "However, there is a
chance that larger rocks survived the trip," Armstrong
said.

A mission to gather material would be tricky.

A robotic rover could sift lunar dust and analyze its
chemistry, hunting for stuff diluted to just seven
parts per million. Because the Moon is mostly dry, the
robot would look for water-bearing minerals. Also,
asteroids that have hit the Moon on their own would
litter it with material high in water and metal, so
the robot would have to look for wet stuff that's low
in metals -- and possibly from Earth.

Armstrong said finding larger terrestrial rocks on the
Moon would be harder and likely require sending
humans.

Back to the Moon

Researchers know that getting back to the Moon is a
tough sell these days.

"It is commonly held that we've already sort of 'done'
the Moon," Armstrong points out. "However, science was
not the main driver of the Apollo mission, and we have
so much left to learn."

He said a lot of planetary science is based on
knowledge gleaned from Apollo missions.

"This [new study] gives us a compelling reason to go
back -- to look at the Moon as a window to early
Earth," he said. "But going to the Moon is the fastest
and cheapest way to learn more about our solar
system."

Finding stuff on the Moon that came from Earth would
also verify the whole premise of the new study,
Armstrong said. This would allow researchers to
accurately date the period of bombardment they suspect
would have put the rocks there in the first place.

Kevin Zahnle, a scientist at NASA's Ames Research
Center who was not involved in the study, agreed that
there might be terrestrial material on the lunar
surface.

"They [the rocks] may tell us something about the
presence or absence of continents [on Earth] 4 billion
years ago," Zahnle said. "There is a very small chance
that one might find a rock that shows unambiguously
that there was life on Earth before 4 billion years
ago."

Scientists are presently debating when life began on
Earth. The most commonly believed time frame, based on
reasonably solid evidence, is 3.8 billion years ago.
Some scientists argue that life is not that old,
however, while others think it began earlier. The
answer bears on the prospects for life having
originated on other planets.

The vault

Zahnle said further investigation into the potential
fruitfulness of a new lunar mission ought to start
with an examination of lunar samples kept in a vault
at the Johnson Space Center in Houston.

More than 2,400 separate bits of the Moon are
sequestered there, ranging from sand grains to
basketball-sized rocks. Other scientists have proposed
such work, Zahnle said, but all requests have been
rebuffed.

Armstrong and his colleagues are also seeking access
to the vault but have had no luck. Meanwhile, they've
obtained several grams of fine lunar particles from
another researcher.

"This gives us thousands if not millions of grains to
test some of our ideas about how to go about searching
for this stuff," Armstrong said. "I have no illusions
about finding Earth material in that sample, but it
gives us a place to hone our techniques."

Ultimately, Zahnle said, the "profound information"
about Earth's past that might be gleaned rummaging
through Earth's attic "is probably impossible to
obtain in any other way," than by going to the Moon.
"Its not that the Moon is a good place to look. It's
rather that the Moon is the only place to look."

     Related SPACE.com STORIES :

 Apollo Moon Rocks: Dirty Little Secrets
 
 30 Years Later, Moon Rocks Retain Their Secrets
 
<http://www.space.com/scienceastronomy/050803_moon_nitrogen.html>
Received on Wed 03 Aug 2005 05:18:07 PM PDT