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Meteor post-mortem

Sun, 10th Nov 2013

Chris Smith

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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. Chelyabinsk meteorite fragment

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.

Thousands of windows were smashed and people 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.



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Something else of interest relating to this event is that some people had retinal burns, and that isn't surprising give that I've also heard in the last few days that it was 30 times brighter than the sun. If you see one of these things, don't stare at it, and bear in mind that a bigger one could be so bright that even a glance could destroy your centre of vision permanently. David Cooper, Sun, 10th Nov 2013

That's interesting, David. Do you have a reference or news source for this? I'd like to follow that up. chris, Sun, 10th Nov 2013

From this YouTube it certainly provided more illumination that the sun* ...

RD, Sun, 10th Nov 2013

I'd like to follow it up too, but I've only heard these slipping into news items either on the radio or TV. I can't pin down where I heard them because I listen to too many different sources, including the BBC World Service. I've heard "retinal burns" being mentioned once without further elaboration, and "30 times as bright as the sun" mentioned once without anything else being said on the matter, and yet this sounds like a really important thing to know about. A really big one that's going to kill everyone would probably blind you even if you had your eyes shut (and might fry all your skin too), but you don't want to be killed by something of intermediate size due to being blinded if it could be survived by finding your way somewhere underground before the shockwave arrives. At the time of the Tunguska event, some people had their clothes set on fire as the shockwave passed, so it's not just a blast you want to get out of the way of. Anyway, I think that spreading the word about the danger of looking at these things could prevent unnecessary damage to people's eyes and may save lives too, so it matters. I'm also worried about the risk of looking at Betelgeuse if it blows, because you don't feel pain when the retina burns. David Cooper, Mon, 11th Nov 2013

In this page there's a reference to severe burns which I suspect refers to retinas although it doesn't say so. It might be better to get someone who speaks Russian to do the searching for more info on this, because most of the useful stuff on this will be in that language. David Cooper, Tue, 12th Nov 2013

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