Meteor post-mortem

Using videos posted on the Internet, a Czech team have reconstructed and traced the origins of the asteroid fragment that devastated a Russian city earlier this year...

The Chelyabinsk meteor, as it is now known in honour of the city where it struck, broke up in the air on February 15th 2013, unleashing a shockwave packing energy equivalent to half a million tonnes of TNT.

成千上万的玻璃被打碎,背影e injured as the airblast ripped through the metropolis.

An 8 metre hole which appeared in the ice of lake Chebarkul 70km to the west is thought to indicate the final watery resting place of what remained of the object that caused the blast.

Now, writing in Nature, Lukas Shrbeny and his colleagues at the Academy of Sciences of the Czech Republic have used 15 publically-available videos of the passing impactor to estimate its size and proportions, plot its trajectory and speculate about its origins.

Calibrating the video sequences by using the positions of identifiable stars, and using the sonic booms documented on the video soundtracks to chart the break-up of the object, the Czech team's results suggest that a house-sized object of roughly 10 million tonnes and travelling at over 19 kilometres per second slammed into Earth's atmosphere and began to fragment.

At between 30-40 kilometres up it broken into 20 boulders about 10,000 tonnes apiece before severe disintegration occurred at an altitude of 22 kilometres leaving one dominant 500 tonne object that ultimately plopped into Lake Chebarkul. Intriguingly, the results suggest that, before it hit the Earth, the object would have shared a close orbit with a known NEO (near-Earth object), an asteroid called 86039.

A collision with, they speculate, another object dislodged a chunk of 86039, dispatching it on an Earth-bound course.

Already weakened and fractured by this earlier event, the combined pressures of smashing into the atmosphere and the heating from friction with the air, caused the object to disintegrate explosively.