[meteorite-list] The moon, meteorites, and quotes from a newer list member

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Sat Sep 2 02:09:05 2006
Message-ID: <bv7if2hondsq243l4cg04ki1lbd7j977jq_at_4ax.com>

Begging a crust
NASA has a lot of moon rock, but is it enough?
Lucy Heady

There's an unassuming building at the Johnson Space Center in Houston, Texas,
that is home to some exceedingly precious rubble: more than 300 kilograms of
lunar rock.

The grey fragments of Moon range from fine grains of sand to rocks the size of
basketballs. They were brought back between 1969 and 1976, mainly by the US
Apollo missions, along with a tiny amount from Russia's robotic Luna missions.

Since their arrival, these rocks have helped scientists to understand much of
what we know about the Moon today. Data from them were crucial in supporting the
idea that the Moon was formed by a giant impact with the early Earth, for
example.

You might think that after 30 years of analysing and reanalysing these samples
mission scientists have learned all they could possibly want know.

Not so, says Randy Korotev of Washington University in St Louis. "People are
developing new techniques all the time, which are helping us to pinpoint the
dates of pivotal events in the Moon's history," he says. In 2005, for example,
fragments of Apollo rock were used to pin down the exact age of the Moon1.
Analysis of the elements halfnium and wolfram in the rock showed that the Moon
is 4.527 billion years old, give or take 10 million years ? an improvement over
previous datings of 4.56 to 4.29 billion years.

Rock on

There is a reasonable ? but not unlimited ? amount of rock around for more
studies.

In total, 382 kilograms of rock have been brought back from the Moon, 99.9% of
it by the Apollo missions. About 85% of this is still in storage (mostly at
Johnson, with a small amount elsewhere for safe keeping) and has never been
exposed to Earth's air. The United States has given away only a tiny proportion
of its store (see 'Scattered fragments'), and of the rock that has been loaned
out for educational purposes or research, only 1% or so has been destroyed.

The samples in storage are kept in a dry nitrogen atmosphere to prevent
degradation. And, after a decision made in the 1970s, only three materials -
stainless steel, aluminium and Teflon ? have ever been allowed to come in
contact with them: these materials can be easily identified and separated from
the lunar rock.

Nevertheless, just 1% of the rock at stored at the Johnson Space Center matches
up to the strict definition of 'pristine'.

Perfect pebbles

"Pristine rocks are those that have not been altered or changed by the process
that broke them free from the Moon's surface" explains Gary Lofgren, lunar
curator at Johnson. That rules out most samples simply because they are
volcanic, and having been belched from a volcano are no longer original crust,
or because they have been smashed around by meteoric impacts.

In truly pristine samples, says Lofgren, "the minerals within the rock have not
been disordered; it is an original piece". This enables scientists to get a true
picture of the processes that formed the Moon. And whenever new tests are
developed, scientists are keen to try them out on pristine rock.

"In the next five to ten years the scarcity of pristine lunar material will be a
real problem; we could easily be in the situation of turning down good research
proposals," Lofgren warns.

The right variety

It's not just quantity and quality that lunar geologists want, they need a
better range of rocks too.

The Apollo missions landed in a relatively small area of the Moon near the
equator, on the Earth-facing side. Scientists have since discovered that this
area has an unusually high concentration of radioactive chemicals, making the
samples unrepresentative of the Moon as a whole.

Lunar meteorites can help to provide information about other parts of the Moon,
but these have been altered by whatever process chipped them from the Moon's
surface and their entry into our atmosphere. And one cannot tell exactly where
such bits of rock have come from.

When the Apollo missions were launched, "all we had to guide sample collection
were photographs and some spectrum data from Earth-based telescopes", says
Korotev. "Now we are a lot more aware of where the interesting sites are".

Likely targets

The South Pole-Aitken basin is one tempting site: photographic evidence suggests
it is the oldest visible meteorite impact2. Measuring the age of the rock here
could help to put a date on when the Moon's crust formed. And samples from the
lunar poles would reveal whether there is or is not any water on the Moon.

So do President George W. Bush's plans to return to the Moon and head on to Mars
offer hope to geologists? Korotev isn't overly optimistic.

"NASA's plan for planetary exploration is not science driven, it's driven by the
aim of getting to Mars. It is true that samples from anywhere not near the
Apollo landing sites would give us new information but they wouldn't necessarily
help answer a specific question," he says. It may take a long time to tick off
Korotev's wish list.
Received on Sat 02 Sep 2006 02:10:17 AM PDT