An object that exploded over Chelyabinsk, Russia in February 2013 initially measured 20-m across and was about 4,452 million years old, according to three new papers published online in journals Science and Nature.
This photograph shows the meteor streaking through the sky above Chelyabinsk, Russia. Image credit: M. Ahmetvaleev.
“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,” explained Dr Olga Popova from the Russian Academy of Sciences in Moscow, who is a co-author of a paper published in the journal Science.
The meteor’s brightness peaked at an altitude of 29.7 km as the object exploded. For nearby observers it briefly appeared brighter than the Sun and caused some severe sunburns. Scientists 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 to 6 tones, 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 kg, was recovered from the bed of Lake Chebarkul in October by Russian scientists.
Shockwaves from the airburst broke windows, rattled buildings and even knocked people from their feet. The researchers visited over 50 villages in the area and found that the shockwave caused damage about 90 km 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 km 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.
The researchers also carried out chemical and isotopic analysis of the meteorites. They measured the magnetic properties of metallic grains in the meteorite.
Put together, new data confirmed that the Chelyabinsk object was an ordinary chondrite, about 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.
The team 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.
The researchers 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.
They speculate 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,” said Dr Peter Jenniskens, a meteor astronomer with SETI Institute and co-author of Science paper.
“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,” added Prof Qing-Zhu Yin from the University of California, Davis, a co-author of Science paper.
More details are given in two papers published online in the journal Nature (paper 1 and paper 2).
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Bibliographic information: Olga Popova et al. Chelyabinsk Airburst, Damage Assessment, Meteorite Recovery, and Characterization. Science, published online November 7, 2013
Jiří Borovička et al. The trajectory, structure and origin of the Chelyabinsk asteroidal impactor. Nature, published online before print November 2013; doi: 10.1038/nature12671
Brown PG et al. A 500-kiloton airburst over Chelyabinsk and an enhanced hazard from small impactors. Nature, published online before print November 2013; doi: 10.1038/nature12741
