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@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@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@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.