[meteorite-list] First Study of Chelyabinsk Meteorite

[Ron Baalke]

http://news.ucdavis.edu/search/news_detail.lasso?id=10764

First study of Russian meteorite
UC Davis Press Release
November 6, 2013

The meteor that exploded over Chelyabinsk, Russia, in February 2013 was 
"a wake-up call," according to a University of California, Davis, scientist 
who participated in analyzing the event. The work is published Nov. 7 
in the journal Science by an international team of researchers.

"If humanity does not want to go the way of the dinosaurs, we need to 
study an event like this in detail," said Qing-zhu Yin, professor in the 
Department of Earth and Planetary Sciences at UC Davis.

Chelyabinsk was the largest meteoroid strike since the Tunguska event 
of 1908, and, thanks to modern technology from consumer video cameras 
to advanced laboratory techniques, provides an unprecedented opportunity 
to study such an event, the authors note.

The Chelyabinsk meteorite belongs to the most common type of meteorite, 
an "ordinary chondrite." If a catastrophic meteorite strike were to occur 
in the future, it would most likely be an object of this type, Yin said.

The team was led by Olga Popova of the Russian Academy of Sciences in 
Moscow, and by NASA Ames and SETI Institute meteor astronomer Peter Jenniskens, 
and included 57 other researchers from nine countries.

"Our goal was to understand all circumstances that resulted in the damaging 
shock wave that sent over 1,200 people to hospitals in the Chelyabinsk 
Oblast area that day," said Jenniskens. The explosion was equivalent to 
about 600 thousand tons of TNT, 150 times bigger than the 2012 Sutter's 
Mill meteorite in California.

Based on viewing angles from videos of the fireball, the team calculated 
that the meteoroid entered Earth's atmosphere at just over 19 kilometers 
per second, slightly faster than had previously been reported.

"Our meteoroid entry modeling showed that the impact was caused by a 20-meter 
sized single chunk of rock that efficiently fragmented at 30 km altitude," 
Popova said. (A meteoroid is the original object; a meteor is the "shooting 
star" in the sky; and a meteorite is the object that reaches the ground.)

The meteor's brightness peaked at an altitude of 29.7 km (18.5 miles) 
as the object exploded. For nearby observers it briefly appeared brighter 
than the sun and caused some severe sunburns.

The team estimated that about three-quarters of the meteoroid evaporated 
at that point. Most of the rest converted to dust and only a small fraction 
(4,000 to 6,000 kilograms, or less than 0.05 percent) fell to the ground 
as meteorites. The dust cloud was so hot it glowed orange.

The largest single piece, weighing about 650 kilograms, was recovered 
from the bed of Lake Chebarkul in October by a team from Ural Federal 
University led by Professor Viktor Grokhovsky.

Shockwaves from the airburst broke windows, rattled buildings and even 
knocked people from their feet. Popova and Jenniskens visited over 50 
villages in the area and found that the shockwave caused damage about 
90 kilometers (50 miles) on either side of the trajectory. The team showed 
that the shape of the damaged area could be explained from the fact that 
the energy was deposited over a range of altitudes.

The object broke up 30 kilometers up under the enormous stress of entering 
the atmosphere at high speed. The breakup was likely facilitated by abundant 
"shock veins" that pass through the rock, caused by an impact that occurred 
hundreds of millions of years ago. These veins would have weakened the 
original meteoroid.

Yin's laboratory at UC Davis carried out chemical and isotopic analysis 
of the meteorites. Professor Ken Verosub, also of the Department of Earth 
and Planetary Sciences, measured the magnetic properties of metallic grains 
in the meteorite. Doug Rowland, project scientist in the Center for Molecular 
and Genomic Imaging at the UC Davis Department of Biomedical Engineering, 
contributed X-ray computed tomography scanning of the rock.

Put together, these measurements confirmed that the Chelyabinsk object 
was an ordinary chondrite, 4,452 million years old, and that it last went 
through a significant shock event about 115 million years after the formation 
of the solar system 4,567 million years ago. That impact was at a much 
later date than in other known chondrites of the same type, Yin said, 
suggesting a violent history.

Jenniskens calculated that the object may have come from the Flora asteroid 
family in the asteroid belt, but the chunk that hit the Chelyabinsk area 
was apparently not broken up in the asteroid belt itself. Researchers 
at the University of Tokyo and Waseda University in Japan found that the 
rock had been exposed to cosmic rays for only about 1.2 million years, 
unusually short for rocks originating in the Flora family.

Jenniskens speculates that Chelyabinsk belonged to a bigger "rubble pile" 
asteroid that broke apart 1.2 million years ago, possibly in an earlier 
close encounter with Earth.

The rest of that rubble could still be around as part of the near-earth 
asteroid population, Jenniskens said.

Yin noted that major meteorite strikes like Tunguska or Chelyabinsk occur 
more frequently than we tend to think. For example, four tons of material 
were recovered from a meteor shower in Jilin, China in 1976.

"Chelyabinsk serves as unique calibration point for high energy meteorite 
impact events for our future studies," he said. Technology for early detection 
of these objects is needed, Yin said -- such as the Large Synoptic Survey 
Telescope, currently being developed by an international team headed by 
UC Davis physics professor J. Anthony Tyson.

The work was supported by the Russian Academy of Sciences, the Office 
of the Governor of Chelyabinsk Oblast, NASA and the Academy of Finland.

About UC Davis

For more than 100 years, UC Davis has engaged in teaching, research and 
public service that matter to California and transform the world. Located 
close to the state capital, UC Davis has more than 33,000 students, more 
than 2,500 faculty and more than 21,000 staff, an annual research budget 
of nearly $750 million, a comprehensive health system and 13 specialized 
research centers. The university offers interdisciplinary graduate study 
and more than 100 undergraduate majors in four colleges - Agricultural 
and Environmental Sciences, Biological Sciences, Engineering, and Letters 
and Science. It also houses six professional schools - Education, Law, 
Management, Medicine, Veterinary Medicine and the Betty Irene Moore School 
of Nursing.

Media contact(s):

 * Qing-zhu Yin, Earth and Planetary Sciences, (530) 220-4076, qyin at ucdavis.edu
 * Andy Fell, UC Davis News Service, (530) 752-4533, ahfell at ucdavis.edu