[meteorite-list] NASA and International Researchers Obtain Crucial Data from Meteoroid Impact (Chelyabinsk)

[Ron Baalke]

November 6, 2013

Dwayne Brown
Headquarters, Washington      
202-358-1726
dwayne.c.brown at nasa.gov

Rachel Hoover
Ames Research Center, Moffett Field, Calif. 
650-604-4789
rachel.hoover at nasa.gov

Karen Randall
SETI Institute
650 960-4537
krandall at seti.org

RELEASE 13-327

NASA and International Researchers Obtain Crucial Data from Meteoroid Impact

A team of NASA and international scientists for the first time have gathered 
a detailed understanding of the effects on Earth from a small asteroid 
impact. 

The unprecedented data obtained as the result of the airburst of a meteoroid 
over the Russian city of Chelyabinsk on Feb. 15, has revolutionized scientists' 
understanding of this natural phenomenon.

The Chelyabinsk incident was well observed by citizen cameras and other 
assets. This factor provided a unique opportunity for researchers to calibrate 
the event, with implications for the study of near-Earth objects (NEOs) 
and the development of hazard mitigation strategies for planetary defense. 
Scientists from nine countries now have established a new benchmark for 
future asteroid impact modeling. 

"Our goal was to understand all circumstances that resulted in the shock 
wave," said meteor expert Peter Jenniskens, co-lead author of a report 
published in the journal Science.

Jenniskens, a meteor astronomer at NASA's Ames Research Center and the 
SETI Institute, participated in a field study led by Olga Popova of the 
Institute for Dynamics of Geospheres of the Russian Academy of Sciences 
in Moscow in the weeks following the event.

"It was important that we followed up with the many citizens who had firsthand 
accounts of the event and recorded incredible video while the experience 
was still fresh in their minds," said Popova. 

By calibrating the video images from the position of the stars in the 
night sky, Jenniskens and Popova calculated the impact speed of the meteor 
at 42,500 mph (19 kilometers per second). As the meteor penetrated through 
the atmosphere, it fragmented into pieces, peaking at 19 miles (30 kilometers) 
above the surface. At that point the superheated meteor appeared brighter 
than the sun, even for people 62 miles (100 kilometers) away.

Because of the extreme heat, many pieces of the meteor vaporized before 
reaching Earth. Scientists believe that between 9,000 to 13,000 pounds 
(4,000 to 6,000 kilograms) of meteorites fell to the ground. This amount 
included one fragment weighing approximately 1,400 pounds (650 kilograms). 
This fragment wasrecovered from Lake Chebarkul on Oct. 16 by professional 
divers guided by Ural Federal University researchers in Yekaterinburg, 
Russia.

NASA researchers participating in the 59 member consortium study suspect 
the abundance of shock fractures in the rock contributed its breakup in 
the upper atmosphere. Meteorites made available by Chelyabinsk State University 
researchers were analyzed to learn about the origin of the shock veins 
and their physical properties. Shock veins are caused by asteroid collisions. 
When asteroid collide with each other, heat generated by the impact causes 
iron and nickel components of the objects to melt. These melts cool into 
thin masses, forming metal veins - shock veins - in the objects.

"One of these meteorites broke along one of these shock veins when we 
pressed on it during our analysis," said Derek Sears, a meteoriticist 
at Ames.

Mike Zolensky, a cosmochemist at NASA's Johnson Space Center in Houston, 
may have found why these shock veins (or shock fractures), were so frail. 
They contained layers of small iron grains just inside the vein, which 
had precipitated out of the glassy material when it cooled.

"There are cases where impact melt increases a meteorite's mechanical 
strength, but Chelyabinsk was weakened by it," said Zolensky.

The impact that created the shock veins may have occurred as long ago 
as 4.4 billion years. This would have been 115 million years after the 
formation of the solar system, according to the research team, who found 
the meteorites had experienced a significant impact event at that time.

"Events that long ago affected how the Chelyabinsk meteoroid broke up 
in the atmosphere, influencing the damaging shockwave," said Jenniskens.

NASA's Near-Earth Object Program sponsors research to better understand 
the origin and nature of NEOs. These essential studies are needed to inform 
our approach to preparing for the potential discovery and deflection of 
an object on a collision course with the Earth.

NASA's recently announced asteroid initiative includes the first mission 
to capture and relocate an asteroid, as well as a grand challenge to find 
and characterize all asteroid threats to human population. It represents 
an unprecedented technological feat that will lead to new scientific 
discoveries and technological capabilities that will help protect our 
home planet.

Aside from representing a potential threat, the study of asteroids and 
comets represent a valuable opportunity to learn more about the origins 
of our solar system, the source of water on the Earth, and even the origin 
of organic molecules that lead to the development of life.

For more information about the Chelyabinsk field study visit:

http://cams.seti.org/index-chelyabinsk.html

For more information on asteroids and comets, visit:

http://www.nasa.gov/asteroids

For more information about NASA, visit:

http://www.nasa.gov

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