[meteorite-list] New Lunar Meteorite Found in Antarctica (MIL 05035)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Sep 14 20:08:45 2006
Message-ID: <200609142315.QAA17055_at_zagami.jpl.nasa.gov>

http://www.eurekalert.org/pub_releases/2006-09/cwru-nlm091406.php

Public release date: 14-Sep-2006

Contact: Susan Griffith
susan.griffith_at_case.edu
216-368-1004
Case Western Reserve University

New lunar meteorite found in Antarctica

Although last year's inclement weather resulted in fewer Antarctic
meteorite recoveries than usual, scientists have recently discovered
that one of the specimens is a rare breed -- a type of lunar meteorite
seen only once before.

The new specimen was found by a field party from the U.S. Antarctic
Search for Meteorites program (ANSMET) headquartered at Case Western
Reserve University. The meteorite was discovered on Dec. 11, 2005, on an
icefield in the Miller Range of the Transantarctic Mountains, roughly
750 km from the South Pole. This 142.2 g black rock, slightly larger
than a golfball and officially designated MIL 05035, was one of 238
meteorites collected by ANSMET during the 2005-2006 austral summer.
Heavy snows limited search efforts during much of the remainder of the
six-week field season, making this meteorite, discovered just 600 m from
camp, a particularly welcome find.

Scientists involved in classification of Antarctic finds at NASA's
Johnson Space Center and the Smithsonian Institution's National Museum
of Natural History said the mineralogy and texture of the meteorite are
unusual. The new specimen is a very coarse-grained gabbro, similar in
bulk composition to the basaltic lavas that fill the lunar maria, but
its very large crystals suggest slow cooling deep within the Moon's
crust. In addition, the plagioclase feldspar has been completely
converted to glass, or maskelynite, by extreme shock (presumably impact
events). The new specimen most closely resembles another Antarctic
meteorite, Asuka 881757, one of the oldest known lunar basalt samples.

Like the other lunar meteorites, MIL 05035 is a piece of the Moon that
can be studied in detail in the laboratory, providing new specimens from
a part of the lunar surface not sampled by the US Apollo program. Many
researchers believe that Apollo visited some of the most unusual and
geochemically anomalous regions of the Moon, and lunar meteorites,
knocked off the surface of the Moon by random impacts, give us samples
that are more representative of the Moon as a whole. The highly-shocked
nature of MIL 05035 suggests an old age and may provide new constraints
on the early intense bombardment of the Earth-Moon system, improving our
understanding of the history of the Earth's nearest neighbor and aiding
NASA's efforts toward a return to the Moon.

Following the existing protocols of the U.S. Antarctic meteorite
program, scientists from around the world will be invited to request
samples of the new specimen for their own detailed research. Details
concerning initial characterization of the specimen and sample
availability are available through the Antarctic Meteorite Newsletter,
available on the Web at
(http://curator.jsc.nasa.gov/curator/antmet/amn/amn.htm) and mailed to
researchers worldwide.

Discovery of this meteorite occurred during the fourth full field season
of a cooperative effort by the National Science Foundation (NSF) and the
National Aeronautics and Space Administration (NASA) to enhance recovery
of rare meteorite types in Antarctica, in the hopes new martian samples
would be found.

###

The US Antarctic Meteorite program is a cooperative effort jointly
supported by NSF, NASA and the Smithsonian Institution. Antarctic field
work is supported by grants from NSF and NASA to Case Western Reserve
University; initial examination and curation of recovered Antarctic
meteorites is supported by NASA at the Astromaterials Curation
facilities at the Johnson Space Center in Houston, Texas; and initial
characterization and long term curation of Antarctic meteorite samples
is supported by NASA and the Smithsonian Institution's National Museum
of Natural History in Washington, D.C.

FURTHER INFORMATION:

Questions regarding the recovery of meteorites in Antarctica should be
directed to the ANSMET website at http://geology.cwru.edu/~ansmet/, or
to Dr. Ralph Harvey at Case Western Reserve University (216-368-0198;
rph_at_case.edu .

Questions regarding the initial processing of Antarctic meteorite
samples and their availability for study should be directed to the
Astromaterials Curation website at
http://curator.jsc.nasa.gov/curator/antmet/antmet.htm or to Dr. Kevin
Righter (281-483-5125; kevin.righter-1_at_nasa.gov).

Questions regarding the initial characterization of the MIL 05035 sample
should be directed to Dr. Timothy McCoy at the Smithsonian Institution
(202-633-2206; mccoyt_at_si.edu).

More information about Antarctic meteorites and Apollo lunar samples can
be found at NASA Johnson Space Center's Astromaterials Curation website
(http://curator.jsc.nasa.gov). A compendium of lunar meteorite
information, maintained by Research Associate Professor Randy Korotev of
Washington University in St. Louis can be found at
http://epsc.wustl.edu/admin/resources/moon_meteorites.html.

Pictures associated with this press release, and their captions, follow.
These images are also available for download at
http://geology.cwru.edu/~harvey/MIL05035.

Figure 1 (MIL 05035 release fig1.jpg) is the field portrait of the
specimen, taken immediately after its discovery. The image shows the
meteorite with its glossy black fusion crust (a melted layer produced
during its descent through the Earth's atmosphere) resting on snow atop
the blue ice of the Miller Range icefields. The device being held above
the meteorite is a counter used to assign a temporary field number to
the find for bookkeeping purposes, and it also serves as a measuring
device. The meteorite was found on December 11th, 2005, about 600 m from
ANSMET's camp. Image courtesy of the Antarctic Search for Meteorites
Program, Case Western Reserve University.

Figure 2 (MIL 05035 release fig2.jpg) shows the new meteorite specimen
in the Antarctic Meteorite Processing Laboratory at NASA's Johnson Space
Center. The meteorite was broken open for initial characterization,
revealing a pinkish-tan interior and a granular texture unusual in
meteorites. The cube in the images is 1 cm on a side and is used to
establish a consistent frame of reference for the geometry of the
specimen; labeling the top, bottom, sides, etc.

Figure 3 (MIL 05035 release fig3.jpg) is a microscopic view of a
thin-section of the meteorite. Geologists routinely create thin sections
(30-micrometer-thick slices) of meteorites and view them in polarized
light to reveal the microscopic texture, crystallinity and mineralogy of
the specimen. The white bar in the lower left is approximately 1
millimeter in length.

In this polarized light view, we see the main constituents of the rock,
the mineral pyroxene (brightly colored and mosaicized) and maskelynite
(dark dull grey), a material formed when the mineral feldspar is
converted to glass by high levels of shock. The mineralogy is typical of
a planetary basalt; but the relatively coarse grain size and the
presence of maskelynite are unusual for lunar specimens, suggesting this
rock represents a time period in the Moon's history poorly recorded by
other lunar samples.


 
Received on Thu 14 Sep 2006 07:15:26 PM PDT