[meteorite-list] The Antarctic Meteorites: Classification and Curation at the Smithsonian Institution

From: Shawn Alan <photophlow_at_meteoritecentral.com>
Date: Mon, 15 Mar 2010 03:56:30 -0700 (PDT)
Message-ID: <285385.80761.qm_at_web113605.mail.gq1.yahoo.com>

Morning Listers,

Here is an article from the 41 Lunar and Planetary Science Conference about the Smithsonian and the challenges they face on the large numbers of meteorites they have to classify?from Antarctic.?
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?The Antarctic Meteorites: Classification and Curation at the Smithsonian Institution. C. M. Corrigan1, L. C.
Welzenbach1, T. J. McCoy1, 1 Department of Mineral Sciences, National Museum of Natural History, Smithsonian
Institution, Washington, DC 20560-0119, USA; corriganc at si.edu.
?
A Relentless Onslaught: Over the past decade,
we have classified between 450-1000 Antarctic mete-
orites per year (Figure 1). This pace, and the variabili-
ty in staffing levels in the Antarctic Meteorite Program
over the past ten years, has caused us to make a few
changes at the Smithsonian. We have now entered a
period of relative stability following the hire of the
author (Corrigan) who has been tasked with managing
the day-to-day activities of the Antarctic meteorite
collection. In addition, we have implemented some
improvements aimed at both saving time and creating a
more robust classification process. The first of these
includes a ?first-pass? classification during initial han-
dling at the Smithsonian, during which we give a pre-
liminary grouping to each meteorite (ordinary chon-
drite, carbonaceous chondrite, achondrite) which al-
lows us to separate out those unique types that will
need to be sectioned right away. This initial classifica-
tion is then confirmed or refuted using a variety of
techniques. These include further visual examination
with binocular microscopes for all meteorites, oil im-
mersion of a few olivine grains for equilibrated ordi-
nary chondrites, and thin section examination and mi-
croprobe analyses for other types of meteorites (carbo-
naceous chondrites, enstatite chondrites, achondrites,
iron meteorites and ?unknowns?, which are occasio-
nally found to be terrestrial samples from Antarctic
glacial moraines). Our goal is to have all of the An-
tarctic meteorites classified within two years of their
return from the ice, a standard now codified in a U.S.
Federal Regulation on Antarctic meteorites. In this
context, newly collected meteorites have always ar-
rived before all the previous year?s meteorites have
been classified.
Reducing Complexity while Maintaining Objec-
tivity: A significant challenge to timely classification
is simplifying the process by comparing meteorites
from a single field area. Pairing groups are common
and classification can be accomplished more quickly if
focus is maintained on a single field area. This has
been increasingly challenging during the past few
years, with multiple field parties working in several ice
fields returning meteorites from many geographically
and glaciologically distinct areas in a single year.
While the meteoritics research community tends to
subdivide groupings and attach significance to abun-
dances of different groups, the classifications we com-
plete must have a level of robustness that is consistent
and can be maintained. As examples, we avoid sub-
classifying eucrites and while we attach both chemical
groups and petrologic types to ordinary chondrites
classified with only visual examination and oil immer-
sion, we advise due caution in overinterpreting abun-
dances within these groups. While the overall percen-
tage of ordinary chondrites is probably a robust statis-
tic, comparing abundances of L5 vs. LL4 is fraught
with peril.
Curation of the Antarctic Meteorites: The
meteorites that are returned from Antarctica are, in the
long term, stored and curated by the staff at the Smith-
sonian. On hand (and onsite at the National Museum
of Natural History, NMNH), we house a chip of each
meteorite returned from the ice and the reference thin
section (those used in the initial classification) of each
meteorite of significant scientific interest to the mete-
orite community. All Antarctic meteorites are even-
tually sent from the Johnson Space Center (JSC) to the
Smithsonian for indefinite curation. Exceptions to this
rule are those meteorites of intense scientific interest to
the community (i.e., those that receive a large number
of requests for sampling for research projects from the
community). These meteorites, which include those
on the Meteorite Working Group?s ?special list? (a list
of rare/small designed to prevent the over-allocation of
any individual meteorite), are housed and allocated
from the specialized facilities at JSC. Meteorites are
transferred to the Smithsonian Institution permanently
after three years without requests by the scientific
community and become the responsibility of the SI for
future allocation. At the Smithsonian, meteorites are
housed in a special facility designed for the long-term
curation of meteorites (Figure 2). That facility, which
is fashioned after the Meteorite Processing Lab at
Johnson Space Center, includes stainless steel nitrogen
atmosphere cabinets for the storage of meteorites along
with a larger, updated facility currently under con-
struction. At the current rates of collection, this facili-
ty should be sufficient to house incoming samples for
approximately 20 years. This new facility will also
house the meteorites in a ?Class 10,000? clean room.

The Science of Antarctic Meteorites: Overall,
our job is to provide a preliminary classification of
each meteorite that ANSMET recovers and returns, not
to answer the individual compelling scientific ques-
tions surrounding each meteorite, no matter how tanta-
lizing the meteorite may be. Our overarching goal is
to provide the Antarctic meteorite material to the
scientific community in a timely fashion, with suffi-
cient information that individual researchers can re-
quest the samples that will most benefit their research.
Sample Requests and Education: Sample Re-
quests: Twice a year the newly classified Antarctic
meteorites are announced in the Antarctic Meteorite
Newsletter [2]. Request deadlines are included in the
Newsletter (and are generally about a month after its
publication) as is the link to the sample request form.
The Meteorite Working Group (MWG) meets bian-
nually as well, usually in Houston the weekend after
the LPSC and sometime in September at the NSF
Headquarters in Arlington, VA. All requests for An-
tarctic meteorites that are not considered ?curatorial?
are processed at these meetings and allocations are
completed following the meetings. ?Curatorial? re-
quests (includes iron meteorites and those samples that
have been permanently transferred into the SI collec-
tion) are currently being dealt with individually by the
SI and/or JSC, and many of those are dealt with on a
rolling basis. Additionally, MWG is reviewing some
requests via email between meetings.
Education: In addition to samples being allocated
for research purposes, we also provide samples for
education and public outreach. Many PIs request and
receive samples from the SI collection that are availa-
ble for use in exhibits. Suites of samples have been
put together for classes on meteorite petrology by JSC
and should be requested through the education sample
curator there (currently Mary Luckey). These can be
of immense importance to graduate students who may
otherwise come out of graduate school having seen
only the types of meteorites they work on, or only
spectra of other bodies that may (or may not!) relate to
the actual rocks we have in our collections. Ground
truthing these samples, and putting them into perspec-
tive with other material from throughout the Solar Sys-
tem is a hugely beneficial exercise.
Finally, individual researchers are welcome to
come view thin sections within the SI collection at any
time. We have the facilities for viewing and photo-
graphing the library sections for the Antarctic Mete-
orites. Many individuals have found it invaluable to
sit and spend a few days looking at all of the sections
of one particular type of meteorites, for example.
References: [1] Corrigan C.M. et al. (2008) Work-
shop on Antarctic Meteorites: Search Recovery and
Classification, MAPS 43 Suppl., A180. [2] http://www-
curator.jsc.nasa.gov/antmet/amn/amn.cfm
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http://www.lpi.usra.edu/meetings/lpsc2010/pdf/2332.pdf
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Shawn Alan
Received on Mon 15 Mar 2010 06:56:30 AM PDT