[meteorite-list] First Study of Chelyabinsk Meteorite

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 6 Nov 2013 12:43:34 -0800 (PST)
Message-ID: <201311062043.rA6KhYWC005340_at_zagami.jpl.nasa.gov>

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
Received on Wed 06 Nov 2013 03:43:34 PM PST