[meteorite-list] Buzzard Coulee . H4 and maybe transitional to H3

From: tett <tett_at_meteoritecentral.com>
Date: Mon, 22 Dec 2008 18:56:22 -0500
Message-ID: <49502926.9060607_at_rogers.com>

Another new article.

http://www.physorg.com/news149168723.html

A University of Calgary-organized team recovered more than one hundred
meteorites from the November 20 meteorite fall southwest of
Lloydminster, Saskatchewan/Alberta, which is expected to set a new
Canadian record for the largest recorded meteorite fall.

"Finding all we could before the snow came on December 6 was a real
challenge and tough on searchers with wind chills routinely colder than
? degrees," said Dr. Alan Hildebrand, holder of the Canada Research
Chair in Planetary Science. "We did as well as we did by collaborating
with experienced researchers from The University of Western Ontario
including Dr. Phil McCausland and Dr. Peter Brown." Both Hildebrand and
Brown are veterans of the Tagish Lake (2000) and St-Robert (1994)
meteorite recovery efforts and McCausland is a veteran of the Tagish
Lake recovery.

Volunteer searchers numbered up to twenty people per day including local
residents, U of C staff and graduate & undergraduate students,
professors from the University of Saskatchewan and the University of
Regina, amateur astronomers from the Saskatoon, Calgary and Edmonton
Centres of the Royal Astronomical Society of Canada, and geoscientists
from ConocoPhillips Canada. Most searchers found at least one meteorite
despite having a thin layer of snow down the last five days.

"The last day that the search teams were out, it snowed all day and we
still found five meteorites which is ridiculous. It shows just how many
are out there," Hildebrand said.

Using the abundance of meteorites on the pond where U of C grad student
Ellen Milley found the first fragments on November 27, Hildebrand
calculated that about 2,000 meteorites of more than 10 grams in size
occur per square kilometer in the northern part of the strewn field, and
probably more than 10,000 meteorites of this size are on the ground
altogether. Many local residents and landowners also found meteorites,
as well as persons from across the prairies and meteorite dealers who
traveled to Saskatchewan to try their luck.

"We have had great cooperation from landowners, who are having a
once-in-a-lifetime experience of a meteorite harvest," Hildebrand said.
"Approximately 130 well-substantiated meteorites have been found
totaling about 40 kg, but probably double that number, weighing more
than 50 kg, have been recovered."

Hildebrand encourages everyone who has collected specimens to please
send him the masses (in grams) and locations (GPS coordinates, NAD27
datum) of their finds to help map the strewn field.

Milley and Hildebrand have formally proposed the name Buzzard Coulee to
describe the fall to the International Meteoritical Society. The name
comes from the picturesque valley near the hamlet of Lone Rock, Sask.
where the first meteorites were discovered.

Typing of the meteorite has been completed with the collaboration of Dr.
Alex Ruzicka and Dr. Melinda Hutson, a husband and wife team at the
Cascadia Meteorite Laboratory at Portland State University, Portland,
Oregon.

"The meteorite is at the low end of the H4 type and may be transitional
with type 3. It will take some more work to sort out everything, but we
have good prospects to learn a lot about the rock's history," Ruzicka said.

A lower number in the classification indicates that a meteorite
experienced less heating on its parent asteroid, making it of more
interest to researchers and potentially to collectors as well. Lower
metamorphic grades are relatively unusual in meteorites of the H, or
"high iron" type, such as the Buzzard Coulee rocks.

Dr. Hutson observed: "The meteorite also appears to show that different
types of material are mixed together in a subtle way, but we will have
to study more thin sections to better understand this. The meteorite is
slightly shocked, so the material was possibly stirred by an impact on
its parent asteroid."

Hand specimens of the meteorite show only rare fragmental texture, but
with the prospect of hundreds of meteorites to study, including some
large ones (the largest recovered to date is approximately 13 kg), more
will be learned about the history of the asteroid fragment that fell at
Buzzard Coulee than for most falls.

"It was a great experience to visit the Cascadia Meteorite Lab to see
how they do things, and it has been fun to apply the things that we
learned in class to a new meteorite fall," said Milley, who is pursuing
her MSc with Hildebrand in the U of C's Department of Geoscience. "It
feels good to be making a real research contribution. When we determine
the orbit we will also know from where in the asteroid belt this rock
originated."

The recovered meteorites are being stored in an inert nitrogen
atmosphere in a clean room in the meteorite lab at the University of
Calgary to prevent weathering by the Earth's atmosphere.

"Since these meteorites are a fresh fall collected early and nearly dry,
they are unweathered for the most part and deserve the best care
anywhere," Milley said.

The U of C researchers and their collaborators will now turn their
attention back to determining the orbit for the space rock. The H4
classification matches the history of meteorite falls of this type that
usually occur during the afternoon or evening. About 8 million years ago
a large impact occurred on an asteroid of H composition and further
studies will be done to see if Buzzard Coulee is another fragment from
that impact. Although orbit evolution is chaotic, determining this
rock's orbit may help locate that impact. Knowing the fireball's exact
trajectory will also help better plan for the spring searching.

"I think that the number of individual meteorites that will be recovered
for Buzzard Coulee will easily set the Canadian record for the largest
fall, but we still don't know how big the biggest meteorite out there
is, so we don't know how much mass we can expect to be recovered of the
approximately 1 tonne that fell," Hildebrand said. The largest Canadian
meteorite fall currently on record dates to 1960 when hundreds of
meteorites fell near Bruderheim, Alberta.

"During the spring before cultivating and seeding, we will try to
organize the biggest meteorite search effort that Canada has ever seen,"
Hildebrand said. "One of our ambitions at the Prairie Meteorite Search
project is to train everyone in the country to recognize meteorites so
more new ones will be discovered, and this is a great opportunity to
introduce hundreds of people to rocks from space."

Source: University of Calgary
Received on Mon 22 Dec 2008 06:56:22 PM PST