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

[tett]

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