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Risk of massive asteroid strike underestimated
Nature Journal   Nov 10, 2013   nature video  

Published on Nov 6, 2013

In February 2013, an asteroid smashed into Earth near the town of Chelyabinsk in Russia. The event was captured on film by hundreds of local people and the resulting videos soon found their way onto YouTube. Now, scientists are using the data which they can extract from these videos to study the asteroid.

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The asteroid that exploded on 15 February this year near the city of Chelyabinsk in the Urals region of Russia was the largest to crash to Earth since 1908, when an object hit Tunguska in Siberia. Using video recordings of the event, scientists have now reconstructed the asteroid's properties and its trajectory through Earth’s atmosphere. The risk of similar objects hitting our planet may be ten times larger than previously thought, they now warn.

The fireball’s early-morning flight through the sky over the Urals was observed by many people and captured by numerous video cameras. To observers on the ground, it shone 30 times brighter than the Sun, and had an energy equivalent to more than 500 kilotons of TNT. An analysis of calibrated observations now provides a precise picture of the asteroid’s last ride and reveals surprising details of its likely cosmic origin.

The rock was an ordinary chondrite from the asteroid belt located between the orbits of Mars and Jupiter, as revealed by its trajectory and by its elemental and mineral composition, mainly silicates that formed the Solar System billions of years ago. At the time it entered the atmosphere, its mass was of the order of 12,000–13,000 metric tonnes, report two studies published online today in Nature1 and another study published at the same time in Science2. This is nearly twice as heavy as initial estimates had suggested and also larger than revised estimates published in June.

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