[meteorite-list] Antarctic Meteorites: Chip Off the Red Planet (MIL 03346)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Nov 1 12:29:08 2004
Message-ID: <200411011728.JAA29531_at_zagami.jpl.nasa.gov>

Antarctic meteorites: Chip off the red planet
By Emily Stone
The Antarctic Sun
October 24, 2004

The Antarctic meteorite hunters knew they'd found something good when
they spotted the crusty black rock on a Miller Range ice field last year.

"The field notes said, 'this is very, very, very sexy.' Three verys,"
said Ralph Harvey, head of the U.S. Antarctic Search for Meteorites
program (ANSMET).

The hunters had to wait months before learning what they had discovered.
The fist-sized rock first had to be carefully collected by the 4-person
team, shipped frozen to NASA's Johnson Space Center in Houston, and then
split so that a small chunk could be sent to the Smithsonian Institution
for analysis.

In July, the team learned they'd found a piece of Mars. The piece is a
1.3 billion year- old volcanic meteorite, weighing 715 grams.

Martian meteorites are rare finds. Eleven of the 31 known Mars
meteorites were found here.

This meteorite is particularly valuable because it belongs to a group of
Mars meteorites known as nakhlites. This is the seventh nakhlite on
record. All the nakhlites are believed to have come from the same
volcanic event and are among the oldest known rocks from Mars. They are
named after the Egyptian city of Nakhla, where the first meteorite of
that type was retrieved in 1911 after, as legend goes, fragments struck
and killed a dog there.

The older the rock, the more it can tell scientists about Mars' past,
explained Harvey, a geology professor at Case Western Reserve University
in Cleveland.

"The rock has potentially recorded not only a volcanic event 1.3 billion
years ago, but all of the ensuing activity on Mars," he said, like the
rock's interactions with the planet's fluids and atmosphere. "What
you've got is a little recorder, if you will. That's what us geologists
do ? we play that back."

Eighty-five scientists have requested a small piece of the rock to use
in their own experiments, according to Timothy McCoy, the curator in
charge of the national meteorite collection at the Smithsonian.

The scientists will analyze the samples with different goals, such as
searching for evidence of life, or learning more about Martian
volcanoes. Others might dissolve a piece and measure the different
isotope levels inside.

"There are a lot of little signs there that lead us toward a picture of
the environment of Mars over the last billion years, and that's pretty
cool," Harvey said. "Thirty chunks of rock from 90 billion miles away is
really more than we could ask for. It's a dream."

McCoy, who was in charge of classifying the meteorite, said he could
tell it was a nakhlite as soon as he looked through a microscope at a
one-inch long, hair's width thick piece known as a thin section.
Nakhlites are full of minerals that crystallized in the rocks as they
hardened. Under the microscope, they look like bits of bright stained
glass against a dark background, or like the view through a colorful
kaleidoscope.

"The texture of this type of rock is so distinct that you can't possibly
mistake it for something else," McCoy said. "They're really pretty."

McCoy said this meteorite has clearly interacted with liquid in its
lifetime, but it's not yet clear what kind of liquid. He is one of the
people who requested a sample to analyze more fully. McCoy plans to
compare the new nakhlite to volcanic rock from a lava flow in Ontario,
Canada. That flow is one of the few places on Earth that may be similar
to the flow on Mars where the nakhlite originated. McCoy hopes the
comparison will help determine at what depth in the flow the meteorite
originated.

ANSMET teams have been searching for meteorites in Antarctica since
1976. Meteorites fall evenly all over Earth, but Antarctica is a
particularly good place to look for them. Antarctica's advantage is
two-fold, Harvey explained.

"If you want to find things that fall from the sky, lay out a big white
sheet," he said. "And Antarctica is a big white sheet 3,000-miles across."

The second reason has to do with the way ice flows across the continent.
The meteorites get sprinkled across the ice, and many end up getting
buried over time. The ice is slowly moving toward the sea, but it gets
blocked in places by mountains and forms ice cul-de-sacs. Over millions
of years, the ice surface at those bends evaporates, exposing more and
more meteorites, Harvey said. ANSMET targets these areas for their hunts.

ANSMET sends out two teams a year, a 4-person reconnais - sance team and
an 8-person systematic search team. The reconnaissance team usually
spends a couple days to a week at each site, checking to see if it's
worth returning there. If it's deemed a good spot, a systematic search
team will go there another year and spend the whole season collecting
meteorites.

This year the reconnaissance team will work at a number of ice fields
throughout the mid-range of the Transantarctic Mountains, from the
Zanefeldt Glacier in the south to Buckley Island in the north. The
systematic search team will work at the LaPaz ice fields, approximately
400 km from the South Pole Station.

Last year's reconnaissance team found the nakhlite on Dec. 15, the third
day of its six-week season. The group used snowmobiles to scan the blue
ice field in the Miller Range of the Transantarctic Mountains, about 750
km from the South Pole.

"We just knew it was something unusual," said Nancy Chabot, a research
scientist at Case Western who was on the reconnais - sance team.

The rock was particularly black and quite shiny, Chabot said. The black
crust, called a fusion crust, is created because much of the meteorite's
exterior gets burned off when the meteorite enters Earth's atmosphere
traveling at 10 km to 20 km per second. It also appeared very
crystalline, which Chabot said usually indicates that the rock came from
a planet.

The two ANSMET teams collected a record 1,358 meteorites last season,
Harvey said, including not only the nakhlite but a couple new moon rocks
and some interesting rocks from asteroids as well.

Chabot said there's little doubt about whether it's worth sending the
systematic search team back to the site.

"I can say that definitely with this discovery and the other things we
found at the Miller Range, the answer is yes."

Since 1969, more than 16,000 meteorites have been found in Antarctica,
more than doubling the number available for study. For those working at
or visiting McMurdo Station, there are three types of meteorites on
display at the Crary Laboratory.

NSF-funded research in this story: Ralph Harvey, Case Western Reserve
University, http://geology.case.edu/~ansmet/
Received on Mon 01 Nov 2004 12:28:55 PM PST