Large, Fast and Rare Meteorite hits the Earth

Geology professor Qing-zhu Yin holds a fragment of the Sutter Mill meteorite that exploded over the Sierra foothills this past spring. (Gregory Urquiaga/UC Davis photo).

A meteorite that exploded as a fireball over California's Sierra foothills this past spring was among the fastest, rarest meteorites known to have hit the Earth, and it traveled a highly eccentric orbital route to get here.

An international team of scientists presents these and other findings in a study published Friday, Dec. 21, in the journal Science.

The 70-member team included nine researchers from UC Davis, along with scientists from the SETI Institute, NASA and other institutions.

The researchers found that the meteorite that fell over Northern California on April 22 was the rarest type known to have hit the Earth - a carbonaceous chondrite. It is composed of cosmic dust and presolar materials that helped form the planets of the solar system.

The scientists learned that the meteorite formed about 4.5 billion years ago was knocked off its parent body, which may have been an asteroid or a Jupiter-family comet, roughly 50,000 years ago.

Once it left the comet, it began its journey to Earth and exploded over Sutter's Mill, the gold discovery site that sparked the California Gold Rush.

As it flew toward Earth, it traveled an eccentric course through the solar system, flying from an orbit close to Jupiter toward the sun, passing by Mercury and Venus, and then flying out to hit Earth.

The high-speed, minivan-sized meteorite entered the atmosphere at about 64,000 miles per hour.

The study said it was the fastest, "most energetic" reported meteorite that's fallen since 2008, when an asteroid fell over Sudan.

"If this were a much bigger object and had landed in a more populated area, then this could have been a disaster," said co-author and UC Davis geology professor Qing-zhu Yin. "But, in this case, it is a happy."

Before entering Earth's atmosphere, the meteorite is estimated to have weighed roughly 100,000 pounds but most of that mass burned away when the meteorite exploded. Scientists and private collectors have recovered about 2 pounds remaining.

Alchemy is back - Gold found in Bacterium

Move over, Midas. A genetically modified version of a bacterium that extracts gold from its environment can signal the presence of the precious metal. The result could be a boon for prospectors.

Some bacteria are known to be associated with gold deposits, but it has been unclear whether they play a role in its production – and if so, what that is.

Now Frank Reith of the University of Adelaide, South Australia, has found that dissolved gold is harmful to the bacterium Cupriavidus metallidurans, as it forms a toxic sulphur-containing compound when it is absorbed from the environment. This compound inhibits the bacterium's enzyme function, prompting the distressed microbe to activate a cluster of "gold detox" genes that produce enzymes able to convert the soluble gold compounds into harmless particles of metallic gold.

Hand-held prospector
Knowing how microbes do this will open up a whole new way of prospecting, says co-author Gregor Grass of the University of Nebraska. Reith and Grass have developed a genetically modified version of C. metallidurans that produces a visible response when the detox genes are switched on.

"When the microbes come into contact with gold, they flash a light that can be detected using a hand-held photometer," says Grass. He envisages that prospectors will be able to detect whether gold is present simply by taking a sample of soil and adding modified bacteria to it.

"There have been reports that bacteria can enhance the production of gold for some time," says John Stolz, an environmental microbiologist at the Bayer School of Natural and Environmental Sciences at Duquesne University in Pittsburgh, Pennsylvania. "But this is the first time scientists have actually identified how they do it."

Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0904583106.