A 500-kiloton airburst over Chelyabinsk and an enhanced hazard from small impactors
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Nature Publishing Group
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Most large (over a kilometre in diameter) near-Earth asteroids arenow known, but recognition that airbursts (or fireballs resultingfrom nuclear-weapon-sized detonations of meteoroids in theatmosphere) have the potential to do greater damage than previouslythought has shifted an increasing portion of the residualimpact risk (the risk of impact from an unknown object) to smallerobjects. Above the threshold size of impactor at which the atmosphereabsorbs sufficient energy to prevent a ground impact, most ofthe damage is thought to be caused by the airburst shock wave, butowing to lack of observations this is uncertain. Here we report ananalysis of the damage from the airburst of an asteroid about19 metres (17 to 20 metres) in diameter southeast of Chelyabinsk,Russia, on 15 February 2013, estimated to have an energy equivalentof approximately 500 (6100) kilotons of trinitrotoluene (TNT,where 1 kiloton ofTNT54.18531012 joules).Weshowthat a widelyreferenced technique of estimating airburst damage does notreproduce the observations, and that the mathematical relationsbased on the effects of nuclear weapons—almost always used withthis technique—overestimate blast damage. This suggests that earlierdamage estimates near the threshold impactor size are toohigh.Weperformed a global survey of airbursts of a kiloton ormore(including Chelyabinsk), and find that the number of impactorswith diameters of tens of metres may be an order of magnitudehigher than estimates based on other techniques. This suggestsa non-equilibrium(if the population were in a long-term collisionalsteady state the size-frequency distribution would either follow asingle power law or there must be a size-dependent bias in othersurveys) in the near-Earth asteroid population for objects 10 to50 metres in diameter, and shifts more of the residual impact riskto these sizes.
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(2013) A 500-kiloton airburst over Chelyabinsk and an enhanced hazard from small impactors. Nature, 503:238-241
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4 pages
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