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On a crisp morning last April, a 50-ton asteroid slammed into Earth's atmosphere. It shattered sending pieces raining down on Sutters Mill, California. That's where gold was discovered back in 1848, triggering the Gold Rush.

As NPR's Richard Harris reports, scientists are now publishing their first impressions of this remarkable material from outer space.

RICHARD HARRIS, BYLINE: Ed Allen recalls that the sky was a brilliant blue on the morning of April 22nd.

ED ALLEN: I was out on my hillside burning some branches and so forth, and I heard this sonic boom. And it wasn't just one boom, it was a series of booms, literally right over my head. And it went like this: boom, boom, boom, boom, boom, boom, boom, boom.

HARRIS: He looked up from his yard in the California Gold Country to see if there was an airplane in distress or some such - nope.

ALLEN: I did see a small trail of brown, like, dust way up in the upper atmosphere. It was so unremarkable I didn't put the two together.

HARRIS: But within a day he was able to connect the dots. Reports of an impact were all over the local news. And, as his brother Norm explains, it didn't take long to pinpoint where the remnants had landed.

NORM ALLEN: Apparently the weather radar actually picked it up coming down.

HARRIS: And that impact zone just happened to include the Marshall Gold Discovery State Park, where Ed and Norm are volunteer docents. That's the site of Sutter's Mill, where the California Gold Rush all began. Norm says within days, another rush was on in a state park that just happens to allow visitors to pocket any interesting rocks they might find - gold or otherwise.

ALLEN: There were professional and semi professional meteorite hunters out here, as well as just mom and pop with the kids. In fact, one lady was pushing a baby carriage and found one of the bigger pieces that was found, right off the bat.

HARRIS: The biggest chunk was about the size of a fist. And soon professional scientists were on their way. Leading that pack was Peter Jenniskens, from NASA's SETI institute. SETI being the Search for Extra Terrestrial Intelligence.

PETER JENNISKENS: It became quickly clear that this was a rather exceptional asteroid impact.

HARRIS: Jenniskens had instigated the search of weather radar data to pinpoint the landing site. He also collected photographs and video from a few bystanders in the High Sierra. From those, his team was able to conclude that the object it was apparently a chunk of asteroid, probably weighing 10,000 pounds when it hit the atmosphere, and traveling at blistering speed - 18 miles in a second.

JENNISKENS: And because it came in so fast, very little survived. But because it was so big...

(LAUGHTER)

JENNISKENS: ...we still got to find something

HARRIS: Jenniskens has led the scientific search. He hopped into his car and drove up to the park. On his first day of prospecting, he'd been off beating the bushes for hours near Sutter's Mill without luck. He'd given up for the day.

JENNISKENS: And I'm standing there waiting for my friend to open the car - a little impatient. Then I just a few meters from the car, I see little black rocks on the pavement. And I'm thinking, it can't be. Can it?

HARRIS: But it was. Small bits of this unusual space rock. And it was different from the usual meteorites, which look like Earth rock.

JENNISKENS: Most meteorite falls we're getting on the Earth are from the terrestrial kind of stuff - chunks of rock. This is more interesting. This the type of meteorite that carries organics with it to the Earth , that must have brought in the carbon that you and I are made out of.

HARRIS: It's called a carbonaceous chondrite, which is lighter and more porous than typical meteorites. That means the mineral is very susceptible to water damage once it hits the ground. Jenniskens says scientists were fortunate to have collected chunks so quickly.

JENNISKENS: We actually got to see this type of meteorite in a pristine condition, sort of what you would get if you would go to an asteroid in space and you would collect a sample from this type of an asteroid.

HARRIS: People ultimately collected about two pounds of the Sutter's Mill meteorite. And more than 50 scientists joined up as a consortium to study the rare space rock. Their first report appears in Science magazine. Richard Harris, NPR News.

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