Sutter’s Mill meteorite a rare space treasure

AIRSHIP – Dr. Peter Jenniskens, foreground, peers into an instrument aboard the cabin of a blimp as they search for meteorite over Coloma in April. Photos courtesy NASA

Rare, complex, and super fast, the Sutter’s Mill Meteorite that landed in the Lotus-Coloma area last April 22 has been a scientific treasure trove, according to those who have studied it.

Called a Carbonaceous Chondrite Regolith Breccia (that is, a primitive meteorite rich in carbon compounds and glass spherules or agglutinates), the Sutter’s Mill Meteorite was of a very rare type, making up less than 3 percent of all known meteorites.

Recently the meteorite was the subject of a paper published in the Dec. 21, 2012, issue of Science Magazine. http://cams.seti.org/Science-SOM-SM.pdf

Dr. Peter Jenniskens, a meteor astronomer with the SETI Institute and the NASA Ames Research Center, was the lead author of the research paper in conjunction with 69 other scientists.

It was Jenniskens who led scientists and volunteers in the search for remains of the meteorite. Over the spring they could be seen by the busload sweeping the hills as they scoured it for pieces. He was also the second person to find fragments of it in the parking lot of Henningsen-Lotus Park.

Later an airship was brought in to map the debris field of the meteorite to improve the number of finds.

According to Jenniskens, the meteorite made its mark not only because it “had the biggest impact of an asteroid since one fell in the Sudan in 2008, but because it came in twice as fast. In fact, it had the fastest impact ever from which we have recovered material from the ground.”

He and other scientists estimate Sutter’s Mill was about 3 meters in size, had a pre-atmospheric mass of 40,000 kilograms, and an entry velocity of 64,000 mph. However, only 1 kilogram, or about 2 pounds, of fragments have been recovered so far.

Luckily, most of the meteor broke up when it entered the atmosphere at about 30 miles above sea level. Scientists say that breakup was the equivalent of an explosion of 4 kilotons of TNT.

Jenniskens noted that it was very fortunate it fell in Gold Country because of all the excitement it generated, which in turn attracted scores of people looking for fragments.

Chip off the old block

Jenniskens said the Sutter’s Mill Meteorite was actually part of a bigger asteroid estimated to be 4.5 billion years old and 100 kilometers in size. It’s believed Sutter’s Mill broke off from that asteroid anywhere between 50,000 to 90,000 years ago.

(By way of clarification, an asteroid is a small planet or planetoid. When it enters an atmosphere, it becomes a meteor. If it hits the ground, it is a meteorite.)

Such asteroids are often a mixed bag of very primitive ancient material bombarded with newer debris hurtling through space.

Jenniskens thinks the most likely source of the meteorite is a family of asteroids called Eulalia, which orbit the sun in the asteroid belt between Mars and Jupiter. He bases that conclusion on the low-inclined orbit of the asteroid, indicating it came from a debris field of asteroids.

Subsequent testing revealed the meteorite contained a wide array of carbon-containing compounds and 79 separate chemical elements, including a few amino acids.

Doppler assist

One of the fortunate circumstances in the early recovery of Sutter’s Mill fragments was the assistance they received in the form of radar.

According to the article in Science Magazine, Beale Air Force Base in California and weather radars operated by the U.S. National Climatic Data Centers NEXRAD network were the ones that detected Doppler shifts as they followed the fast-moving daytime fireball that ended up in El Dorado County.

While many saw the fireball or heard its explosion, it was the “radar footprint” over Coloma and Lotus that helped direct the scientists and meteorite hunters to the right place to look, which was particularly important given that rain was forecast for the area.

That use of radar ensured the early recovery of the meteorite fragments and gave scientists the most pristine look, to date, at the surface of a primitive asteroid.

Now radar is used on a regular basis to detect and locate meteor falls so samples can be collected quickly enough to study the amino acids and other compounds that are part of their makeup.

Jenniskens said at present there are anywhere between five and 10 meteor falls a year around the world, but only one in 30 is of a primitive meteor. “Often meteors land in the ocean where there’s no chance of recovery,” he remarked.

The scientist said they aren’t organizing any more group searches but he hopes people will continue to look for fragments of the meteorite since it was local residents who found most of them.

“There are still many pieces out there,” he said. “They are very black and unlike other rocks and will stand out as unusual.”

For those interested, all the known finds are listed on a Website at asima.seti.org/sm along with their weight, date, and who found them.

Jenniskens said he’s willing to come out and give a presentation on what they have learned from the Sutter’s Mill Meteorite. Anyone interested in organizing such a talk can contact him at 650-810-0216 or at Petrus.M.Jenniskens@nasa.gov.

In the meantime, the meteor astronomer hasn’t lost any of his enthusiasm for the meteorite, saying he still has his “Sutter’s Mill Meteor” T-shirt commemorating the event. “It’s a symbol of our search efforts,” he said.

“It was very exciting to get pictures of finds sent to me in Gold Rush country and to get caught up  in what was going on,” he said. ”It’s a wonderful story that really came together.”

Contact Dawn Hodson at 530-344-5071 or dhodson@mtdemocrat.net. Follow @DHodsonMtDemo on Twitter.

Dawn Hodson

Dawn Hodson covers news and features.

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