S&T: Massive Meteorite Found in China

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bystander
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S&T: Massive Meteorite Found in China

Post by bystander » Tue Jul 26, 2011 1:55 am

Massive Meteorite Found in China
Sky & Telescope | Kelly Beatty | 2011 July 22
As the meteorite specialist for the Beijing Planetarium, Baolin Zhang gets all kinds of unusual reports — like the dramatic (but ultimately specious) tale of a peasant woman who recently found a blue-ice "meteorite" in her yard.

But credible reports of a massive, oddly shaped and colored stone in the remote Altai Mountains of Xinjiang Uygur province (in northwest China) got his attention. So earlier this month he assembled a small team to check it out firsthand. The trek was cold and arduous, involving a rented jeep, borrowed horses, and even a camel to cross rugged terrain and rivers still swollen with snowmelt.

On the afternoon of July 16th, after reaching a mountainous crest 9,500 feet (2,900 m) up Zhang and his team finally spotted their objective: a large dark-brown stone jutting from the ground. It took only moments for him to realize what they'd found. "This is a huge iron meteorite," he exulted as cameras recorded the scene.

Based on the size of the oblong portion above ground, 7.5 feet (2.3 m) long and about half as wide, Zhang thinks its mass is roughly 25 tons — and it could perhaps top 30 tons. Such an enormous find would rank as one of the largest meteorites known, perhaps even surpassing China's current record-holder, the 28-ton Armanty iron, found in the same region in 1898.

Apparently the big stone's existence has been well known among locals for decades. A few scrawls of graffiti have been cut into the exterior, which also bears "saw marks" that expose the interior. As Zhang reports, "The surface was shiny silver, and I can clearly see exposed not only the iron-nickel composition but also the unique grid lines," called a Widmanstätten pattern, that are common among iron meteorites.

Interestingly, the meteorite is wedged beneath an even larger granite slab, and apparently both were dragged to their current locations long ago by glaciers. It's not yet clear when or how the massive Xinjiang stone will be excavated — though this would seem too magnificent a prize to simply leave in place. The Armanty iron is on display outside the Xinjiang Geology and Mineral Museum in Urumqi, the region's capital city.

Conceivably, the Xinjiang and Armanty meteorites are part of the same fall; tests should soon establish whether they are siblings or just happen to be enormous unrelated hunks of meteoritic metal that fell to Earth from interplanetary space.
Giant Meteorite Discovered in China
Space.com | 2011 July 25
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Re: S&T: Massive Meteorite Found in China

Post by neufer » Tue Jul 26, 2011 2:29 am

http://astrobob.areavoices.com/?blog=78068 wrote:
Image
The Hoba meteorite near Grootfontein, Namibia is the largest-known
and most massive meteorite found on Earth. It was discovered
by accident when a farmer hit it with his plow.
Image
Meteorite hunter Tim Heitz feels the cosmic joy of
sitting on top of the second largest meteorite
in the world, a 37-ton Campo del Cielo.

<<It’ll be interesting to see if the new meteorite will knock China’s largest and the 4th largest meteorite found on Earth – the Armanty iron – out of 4th place. Armanty was also found in Xinjiang in 1898 and weighs 28 tons. While that’s definitely a possibility, it appears that the Hoba meteorite will still reign supreme as the largest meteorite ever found on Earth. It’s located in Namibia, Africa, and at 60 tons, was so heavy, it was simply left in the ground. Like Armanty, Hoba is an iron-nickel meteorite.

After sitting for years in a hole, the site has been developed by the Namibian government into a tourist center. Lined with concentric stone benches, it looks like a great place to sit down and contemplate just how this monster landed on our planet an estimated 80,000 years ago. Oddly, it left no crater. That may have been due to its flat shape and low angle of entry.

After Hoba, the next largest space rock is a 37-ton specimen of the Campo del Cielo iron meteorite in Argentina. This one fell within human memory some 4,000-5,000 years ago. Campo del Cielo, which means ‘Field of the Sky’, came to the attention of the Spaniards in 1576. Local Indian peoples used pieces of it for their weapons, claiming that the huge ‘rock’ had fallen from the sky. They were right.

Thousands of ‘Campos’, as they’re called, have been discovered since. They’re spread over many miles of terrain that contain the remains of at least a dozen impact craters. Over the past few years, many have been and continue to be offered on auction sites like eBay for very reasonable prices.

Composed of an iron and nickel mix, Campos, like other metal meteorites, feel heavy in the hand and look the way many expect a meteorite to appear. You might be surprised however to learn that the vast majority – 82% – of meteorites seen to fall are chondrites or stony meteorites. Irons only account for about 6% of falls. Stony meteorites are also the most commonly found lying around in the hot deserts of Africa and the Middle East as well as the icy plains of Antarctica.

The largest meteorite in the U.S. resides in the American Museum of Natural History. Called the Cape York (Greenland) iron or Ahnighito, it weighs 34 tons and was transported from Greenland to New York in 1897 by Arctic explorer Robert Peary. You can go right up to it and touch it. Like Campo del Cielo, the local Inuit people once cut off metal from it to use for tools and harpoons.>>
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Re: S&T: Massive Meteorite Found in China

Post by Martin33 » Mon Oct 24, 2011 2:27 pm

I just found this forum through Google and I love it :)

I really like what the Namibian government did with the place. The Hoba meteorite definitely deserves touristic attention. I'd definitely like to go there someday and touch the meteorite.

I also find it interesting that such a huge rock didn't leave any crater, weird but possible.

Martin.

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Re: S&T: Massive Meteorite Found in China

Post by Chris Peterson » Mon Oct 24, 2011 3:04 pm

Martin33 wrote:I also find it interesting that such a huge rock didn't leave any crater, weird but possible.
Cratering is produced when objects impact at supersonic or hypersonic speeds, which (happily!) is very rare. A meteorite this size typically lands at terminal velocity- say 50-100 m/s. That's enough to produce what's called an impact pit- a depression a few centimeters to a few meters deep directly underneath the meteorite. That can result in the partial or complete burial of the specimen, which may only be exposed again after some long period of erosion.
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Re: S&T: Massive Meteorite Found in China

Post by neufer » Mon Oct 24, 2011 3:55 pm

Chris Peterson wrote:
Cratering is produced when objects impact at supersonic or hypersonic speeds, which (happily!) is very rare. A meteorite this size typically lands at terminal velocity- say 50-100 m/s. That's enough to produce what's called an impact pit- a depression a few centimeters to a few meters deep directly underneath the meteorite. That can result in the partial or complete burial of the specimen, which may only be exposed again after some long period of erosion.
[c]. http://www.calctool.org/CALC/eng/aerospace/terminal

China Meteorite:
-----------------------
Mass: ~25000 kg
CS area: ~3.7 m2
Drag coefficient ~2.1
Medium density: 1.5 kg/m3
Gravity: 1

Terminal velocity: ~205 m/s[/c]
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Re: S&T: Massive Meteorite Found in China

Post by Chris Peterson » Mon Oct 24, 2011 4:30 pm

neufer wrote:China Meteorite:
-----------------------
Mass: ~25000 kg
CS area: ~3.7 m2
Drag coefficient ~2.1
Medium density: 1.5 kg/m3
Gravity: 1

Terminal velocity: ~205 m/s
Still far too slow to produce cratering, of course. In reality, the terminal velocity remains unknown (or more accurately, only known within a fairly wide range of possibilities) due to the large uncertainty in the drag coefficient and cross-sectional area during flight, and in the details of flight orientation.
Chris

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