[meteorite-list] Serving Up Meteorites on Ice (Antarctic Meteorites)
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:47:09 2004
Serving Up Meteorites on Ice
Planetary Science Research Discoveries
November 7, 2001
--- Antarctic meteorites provide a continuous and
readily available supply of extraterrestrial materials,
stimulating new research and ideas in cosmochemistry,
planetary geology, astronomy, and astrobiology.
Written by Linda M.V. Martel
Hawaii Institute of Geophysics and Planetology
Annual collections of meteorites from Antarctica are a steady source of new
non-microscopic extraterrestrial material including lunar and Martian
samples and rare and unusual flotsam from asteroids. This article summarizes
research on new kinds of Antarctic meteorites that is not simply changing
how meteorites are classified but causing a revolution in our knowledge of
the materials and processes in the solar nebula, our solar system, and the
formation of asteroids, planets, and ultimately our world. When the
2001-2002 Antarctic Search for Meteorites (ANSMET) field party begins
scouting for meteorites on the ice this season, we will be continuing a
25-year tradition of exploration along the Transantarctic Mountains. As a
new ANSMET meteorite hunter, I will report to PSRD on this season's search
and recovery of specimens and how studies of Antarctic meteorites are
unraveling the secrets of solar system formation.
U. S. Antarctic Search for Meteorites program.
Finding Rocks That Fall From Outer Space
The U. S. Antarctic Search for Meteorites (ANSMET) program is a
collaborative effort of the National Science Foundation (NSF),
NASA, and the Smithsonian Institution. Field collection is supported
currently by a grant from the NSF Office of Polar Programs to
Principal Investigator Dr. Ralph Harvey at Case Western Reserve
University in Cleveland, Ohio. NASA and the Smithsonian Institution
provide for the classification, curation, and distribution of
Antarctic meteorites. All three agencies sponsor research on the
specimens which remain the property of the National Science Foundation.
The Meteorite Working Group (MWG) reviews requests for samples by
scientists of all countries. The MWG is a peer-review committee that
meets twice a year to guide the collection, curation, allocation, and
distribution of the U. S. collection of Antarctic meteorites.
The National Institute for Polar Research (NIPR) in Tokyo manages their own
expeditions to Antarctica and oversees the curation, allocation, and
distribution of Japanese collections of Antarctic meteorites. The Committee
on Antarctic Meteorites, which also meets approximately twice a year,
reviews all requests for meteorite samples. The samples are the property of
the NIPR, and allocations are generally only made for a period of 1 to 2
European expeditions and collection programs in Antarctica include the
Italian (PNRA) and German GANOVEX programs. European specimens currently
curated at the Open University, UK are available for study and can be
requested through the Department of Mineralogy of the Natural History Museum
These international collection programs require nothing less than strategic
trips to the ice by sturdy, trained individuals working together in a
well-coordinated way to survive and succeed in this extraordinary
environment. What motivates us to venture to a place that was only a
hypothesized landmass until it was actually sighted in 1820-21? The thrill
of living in an extreme, remote environment (likened by some to a space
outpost) with a rich history of heroic exploration, for the golden chance of
finding pieces of rock from space that tell stories of creation. From the
beginning, the Antarctic collection programs have aimed to recover large
enough numbers of meteorites each season so that something unusual might be
served up, possibly one day a sedimentary rock from Mars showing evidence of
the planet's watery history.
[Scott tents at Meteorite Hills]
Tents at Meteorite Hills during the 2000-2001 ANSMET
field season. This photo was taken from the helicopter
while two of the planetary geologists, Ben Bussey and
Ralph Harvey, began a six-day reconnaissance trip to
ice fields near Bates Nunatak.
Meteorites Found on the Blue Ice
Since 1976, ANSMET has recovered more than 10,000 specimens from meteorite
stranding surfaces along the Transantarctic mountains. The total number of
Antarctic meteorites is closer to 30,000 when you include Japanese
collections (beginning in 1969) and European collections. This large number
is uncorrected for pairing--when laboratory examinations show that two or
more specimens are actually broken pieces of the same rock. Antarctica (the
highest, driest, coldest, windiest, and emptiest place on Earth) has proven
to be an exceptionally good hunting ground because meteorites that have been
falling on the surface through the millennia become buried in the ice moving
slowly seaward. Where mountains or subsurface obstructions block the forward
movement of the ice, the old, deep ice, laden with meteorites, is pushed up
to the surface against the barrier. Strong katabatic winds (winds blowing
down the slopes) clear the surface of loose ice and snow and aid sublimation
and mechanical erosion which expose the meteorites on the blue ice. These
concentrations of meteorites, called stranding surfaces, are not permanent
but appear and disappear as the ice cap changes.
The Antarctic Meteorite Location and Mapping Project (AMLAMP) maintains
databases of meteorite locations for each ice field searched by ANSMET; see
the map below. The Allan Hills-David Glacier Region includes samples from
Allan Hills, Beckett Nunatak, David Glacier Icefields, Elephant Moraine,
MacKay Glacier Icefields, Outpost Nunataks, and Reckling Moraine. The
Darwin-Byrd Glacier Region includes Bates Nunatak, Derrick Peak, Lonewolf
Nunataks, and Meteorite Hills. The Beardmore Region includes Bowden Neve,
Dominion Range, Geologists Range, Grosvenor Mountains, Lewis Cliff,
MacAlpine Hills, Miller Range, and Queen Alexandra Range. The Wisconsin
Range-Scott Glacier Region includes Gardner Ridge, Graves Nunataks, Klein
Glacier, Mt. Howe, Mt. Prestrud, Scott Glacier Icefield, Wisconsin Range,
and Mt Wisting. The Thiel Mountains-Patuxent Region includes Lapaz Icefield,
Patuxent Range, Pecora Escarpment, Stewart Hills, and Thiel Mountains.
A complete set of maps, meteorite listings, and
explanations are available from AMLAMP.
Samples are identified by location (using a three-letter abbreviation), year
of collection, and unique sample number. For example, the Allan Hills
location is abbreviated as ALH, Elephant Moraine is EET, Queen Alexandra
Range is QUE, and Meteorite Hills is MET. Meteorite ALH 81005 was recovered
in Allan Hills during the 1981-1982 ANSMET field season and was the fifth
rock analyzed in the lab. It was a significant find because it turned out to
be a piece of the Moon. The next paragraphs summarize some of the
extraordinary discoveries enabled by ANSMET.
A Suite from the Moon
Scientists have identified 21 meteorites from the Moon. About half are
from Antarctica and half from hot desert regions. They recognized
the first one, ALH 81005, in 1982 on the basis of chemical, mineralogical,
and isotopic compositions. These rocks provide lunar scientists with
samples from places far from the U. S. Apollo and Russian Luna landing sites,
allowing a much better understanding of the composition of the lunar crust.
More importantly, the mere fact that impacts could blast rocks off the Moon
without melting them, gave some credence to the idea that we might also have
meteorites from Mars. See Randy Korotev's web site at Washington University in
St. Louis for more information about meteorites from the Moon.
The idea that bits of Mars have fallen to Earth was hotly debated from
the late 1970s to the mid-1980s. The evidence centered around the relatively
young ages of a group of rocks called the SNC meteorites. They were a mere
1.3 billion years old, some even younger. Since the Moon's volcanic engine
stopped more than 2 billion years ago, the argument went, these meteorites
must come from a much large body. The logical choice was Mars. The evidence
was circumstantial. All that changed when scientists measured the gases trapped in
melted pockets inside EET 79001, a SNC meteorite found at Elephant Moraine.
The abundances of the gases and the isotopic compositions of them were dead
ringers for the atmosphere of Mars, as measured by the Viking landers in 1976.
The results stopped all arguments about where the SNC meteorites came
from--they are our first Martians. There are now 19 Martian meteorites, six of
which come from Antarctica and seven from hot deserts.
Ureilites may be the most mysterious of all the meteorites. They were named for Novo
Urei, a small rock that fell in Russia in 1886. Until people started collecting
meteorites in hot and cold deserts, only six ureilites were known. All contained
small grains of diamond (a high-pressure form of carbon), along with graphite
(low-pressure carbon). This was a startling discovery because diamonds form at high
pressure. Many scientists proposed that the diamonds formed deep inside a large body.
But as we understood the effects of large impacts, it became clear that the diamonds
were the products of high-pressure shock waves caused by a large impact event on the
ureilite body. The key question became the source of the diamond. Was it originally
present in the rocks as graphite that crystallized along with the silicate
minerals, and was then converted to diamond by shock? Or was the diamond forcibly
[graphite in ureilite ALH83014] injected into the rocks by an impact event?
During the past 15 years or so, the number of ureilites has increased dramatically
from only six to 110. Some of the new ones are not severely damaged by shock and
preserve the original state of the rock and its carbon minerals. Examination showed
that they contain long lath-shaped crystals of graphite intergrown with the silicate
minerals. The intergrowth clearly indicates that the carbon was not mixed in by a shock
event. The original six ureilites fell into distinct groups on the basis of the amount
of FeO (iron oxide) in their olivine and pyroxene. This suggested that the rocks
within a group were related to each other, but unrelated to the other groups. Analyses
of the new samples indicate something different, that there is a complete
gradation in the amount of FeO, not separate groups. The relationships among
the ureilites are not so simple and researchers are continuing to try to
understand the geologic processes on the ureilite parent body.
[metal-rich chondrite HH 237] Leftovers From the Birth of the Solar
Chondrites are meteorites that contain rounded objects (called chondrules) that
cooled very rapidly from a molten state. For a long time most scientists thought
chondrules formed directly in the solar nebula--the cloud of gas and dust surrounding
the primitive Sun. However, chemical and mineralogical properties of chondrules and
experiments designed to reproduce the mineral intergrowths in chondrules showed that they
could not possibly have condensed from a gas. The condensation idea gave way in the 1980s
to the hypothesis that chondrules formed from small aggregations of dust (like those fluffy
dust balls that accumulate under your bed) that were melted by some mysterious process
in the solar nebula. Thus, meteoriticists concluded that chondrules were secondary
Three chondrites found in Antarctica (ALH 85085 and QUE 94411) and the Sahara (Hammadah
al Hamra 237) are changing that view. Investigators in the U. S. and Europe may
have found direct condensates from the solar nebula in those meteorites. Chondrules and
grains of metallic iron-nickel chondrules tell the story of heat and wind in the solar
nebula. The chemical compositions of the chondrules indicate formation from a cloud
that had become enriched in dust before being completely evaporated. When the gas cloud
cooled, the tiny droplets condensed, but were blown into much cooler regions far from the
Sun before they had a chance to acquire moderately volatile elements such as sodium,
potassium, and sulfur. They appear to have accreted into asteroids before other
processes affected them, thus preserving the record of heating and jetting in the nebula
that surrounded the infant Sun. The results support new astrophysical theories of
chondrule and star formation. (For details on these interesting meteorites, see the PSRD
articles: Relicts from the Birth of the Solar System and The Oldest Metal in the Solar
Meteorite Bonanzas in Cold and Hot Deserts
We know that extraterrestrial materials fall randomly on Earth; it is simply
easier to find them in deserts where they are well preserved (due to lack of
weathering) and concentrated on a plain background so that they are easily
recognized. Successful meteorite searches in cold and hot deserts have
dramatically increased the number of meteorite finds. While Antarctica is
the premier cold desert hunting ground, researchers Ralph Harvey (Case
Western Reserve University), Anders Meibom (Stanford University), and
Henning Haack (University of Copenhagen) have been using remote sensing
images to look at Earth's other ice sheet, Greenland, for evidence of
meteorite stranding surfaces. Their work suggests that Greenland would be an
excellent place for future meteorite hunts. Several hot desert regions are
yielding huge numbers of meteorites, namely the Sahara Desert (Algeria and
Libya), the Nullarbor Plains (Western and South Australia), Mojave Desert
(Southern California), and high plains of Texas and New Mexico. The three
most productive areas in the Sahara are the Reg el Acfer in Algeria (at
least 320 meteorites), Dar al Gani (at least 256 meteorites) and Hammahah al
Hamra (at least 520 meteorites) in Libya. Over 200 specimens have been
collected from an unknown Saharan location (undisclosed by the private
collectors). An additional 280 meteorites have been collected in Australia's
To Boldly Look for Meteorites
Antarctic meteorites are collected, preserved, and documented very
carefully. They've proven their extraordinary value to science and to our
understanding of the history of the Solar System from its origin in the
solar nebula to the formation of our Sun and planets. Collecting meteorites
in Antarctica is like going on a field trip to the Moon, Mars, and
asteroids. Last year, the eight ANSMET team members recovered 740 meteorite
specimens during their two-month field trip. This season's team of ten will
return to Meteorite Hills to continue searching this portion of the vast
East Antarctic Ice Sheet. These annual systematic collection programs offer
the best chance of finding Martian meteorites and brand new types of
meteorites inspiring new research, ideas, and discoveries.
[people in Antarctica]
Success! ANSMET 2000-2001 field team.
ANSMET--Antarctic Search for Meteorites program history, descriptions,
ANSMET 2001-2002 Expedition Website photos and journal entries from the
field (available starting Nov. 26, 2001.)
Catalogue of Meteorites; additional ordering information from Cambridge
Exploring Meteorite Mysteries, a teacher's guide with activities for
Earth and Space Sciences for grades 5-12. NASA publication
EG-1997-08-104-HQ. Companion Slide Set.
Harvey, R. P., Meibom A., and Haack H. (2001) Meteorite stranding
surfaces and the Greenland icesheet, Meteoritics and Planetary Science,
v. 36, p. 807-816.
Italian Antarctic Research Program.
Lindstrom, M. M. and Score, R. (1995) Populations, Pairing, and Rare
Meteorites in the U. S. Antarctic Meteorite Collection.
Listing of Antarctic web sites from the Committee for Environmental
Protection, Norwegian Polar Institute.
Meteorites from Antarctica, from the Astromaterials Curation office at
NASA Johnson Space Center.
National Institute of Polar Research, Japan.
Office of Polar Programs, National Science Foundation.
Polar Research, National Science Foundation.
Scientific Committee on Antarctic Research, an inter-disciplinary
committee of the International Council for Science.
Taylor, G. Jeffrey "Relicts from the Birth of the Solar System." PSR
Discoveries. March 2001. http://www.psrd.hawaii.edu/Mar01/relicts.html
Taylor, G. Jeffrey "The Oldest Metal in the Solar System." PSR
Discoveries. September 2000.
Virtual Antarctica History: Chronology
Received on Thu 08 Nov 2001 12:15:25 PM PST