Mysterious California fireball resulted in one of the ‘rarest’ meteorites in history

A close shave is providing astronomers with data.

By Max Sonnenberg, The Space Reporter
Thursday, December 20, 2012

Mysterious California fireball resulted in one of the ‘rarest’ meteorites in history

It’s being called one of the rarest meteorites in history.

Just eight months after a  fireball was spotted lighting up California and Nevada skies, a team of researchers say the cause was one of the rarest bits of cosmic material ever discovered.

Researchers responsible for recovering the small pieces of the meteor that hit northern California say it is was largely a carbonaceous chondrite — one of the rarest types to strike Earth. It is composed of cosmic dust and presolar materials that helped form the planets of the solar system, possibly presenting scientists with an extremely valuable resource for studying the early solar system.

Lead author and meteor astronomer Peter Jenniskens of the SETI Institute and NASA Ames Research Center, Moffett Field, California, noted that the age of the meteor made the specimen extremely rare, saying its age could yield some surprising data.

“[O]nly between 50,000 and 90,000 years ago, while most meteorites originate millions and millions of years ago,” he said.

Astronomers say the meteorite likely formed about 4.5 billion years ago. It was knocked off its parent body, which may have been an asteroid or a Jupiter-family comet, roughly 50,000 years ago. The meteorite’s journey came to a halt in late April, when scientists descended on  Sutter’s Mill, California — the gold discovery site that sparked the California Gold Rush — in an effort to recover fragments of the meteorite.

Jenniskens, who led the scientific search, described the search for the fragments, explaining that they instigated a search of weather radar data to pinpoint the exact landing site. He also worked to collect photographs and video from a few bystanders in the High Sierra, some of whom captured stills of the fireball. The team of scientists also employed the use of seismic equipment at international nuclear weapons detection sites in an effort to better pinpoint the size of the meteorite when it struck Earth.

The details of the meteorite were released in a study on Thursday, and the latest findings represent the conclusion of the eight-month ordeal. According to the published report, Jenniskens and his team estimate that the energy of the exploding fireball was equal to a 4-kiloton blast of an atom bomb. Jenniskens and his colleagues report that the asteroid that hit the atmosphere probably had a mass of some 40,000 kilograms, corresponding to a diameter of 2.5 to four meters. It streaked in from the east before detonating at an altitude of about 48 kilometers, the team of researchers said.

Most notably, Jenniskens says the meteorite hit the Earth’s atmosphere at a blistering speed of nearly 18 miles per second, making it one of the fastest recorded object to strike Earth. Jenniskens noted that the object’s speed likely created enough pressure to break it apart, leaving researchers with just small chunks of rock scattered across a wide area.

“The small three meter-sized asteroid that impacted over California’s Sierra Nevada came in at twice the speed of typical meteorite falls,” said Jenniskens.  “Clocked at 64,000 miles per hour, it hit with the energy of a quarter of a Hiroshima bomb. It was the biggest impact over land since the impact of the four meter-sized asteroid 2008 TC3, four years ago over Sudan.”

Of the estimated 100,000 pound asteroid, less than two pounds was recovered on the ground in the form of 77 meteorites. The biggest was 205 grams, according to NASA.

According to Jenniskens’ team, their focus will now shift to further examining the meteorite pieces. The team says the first step will revolve around studying the chemistry and mineralogy of the collected samples, possibly in an attempt to better understand the early solar system and universe.

“It exhibits considerable diversity of mineralogy, petrography, and isotope and organic chemistry, resulting from a complex formation history of the parent body surface. That diversity is quickly masked by alteration once in the terrestrial environment but will need to be considered when samples returned by missions to C-class asteroids are interpreted,” researchers wrote.

Meanwhile, astronomers around the world are using the event as a cautionary tale. The combined speed and size of the meteorite could have been disastrous, according to researchers involved in the study.

“If this were a much bigger object, it could have been a disaster,” said co-author and UC Davis geology professor Qing-zhu Yin. “This is a happy story in this case. “


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