A 500-kiloton airburst over Chelyabinsk and an enhanced hazard from small impactors
| Autor: | Z. Krzeminski, Milton Garces, Wayne N. Edwards, Lars Ceranna, J. Gill, R. E. Spalding, Pavel Spurný, Läslo Evers, Jelle Assink, L. Astiz, Pieter Smets, D. Uren, Aaron Kingery, Pierrick Mialle, Jiří Borovička, C. D. de Groot-Hedlin, A. Saffer, A. Le Pichon, Rod Whitaker, Rhiannon C. Blaauw, William J. Cooke, Margaret Campbell-Brown, Elizabeth A. Silber, Gabi Laske, Douglas P. Drob, Robert Weryk, Peter Brown, E. Tagliaferri, N. Brachet, David Brown, Danielle E. Moser, Mark Boslough, Michael A. H. Hedlin |
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| Rok vydání: | 2013 |
| Předmět: | |
| Zdroj: | Nature. 503:238-241 |
| ISSN: | 1476-4687 0028-0836 |
| Popis: | The damage caused by the asteroid 17–20 metres in diameter that exploded over Chelyabinsk, Russia, on 15 February 2013 is estimated here to have an energy equivalent to about 500 kilotons of TNT. The fireball that streaked across the skies above Chelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth of information. Two papers in this issue present detailed reconstructions of the Chelyabinsk event. From an analysis of videos, Jiři Borovicka et al. determined the trajectory and velocity of the superbolide with high precision. Its orbit was similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43), suggesting that the two bodies may be part of the same asteroid family. And they show that it broke into small pieces between the altitudes of 45 and 30 kilometres. In the companion paper, Peter Brown et al. analysed the damage caused by the airburst which they estimate was equivalent in energy to the detonation of 400 to 600 kilotons of TNT. They suggest that the number of impactors with diameters of tens of metres was an order of magnitude higher than current estimates, shifting much of the residual impact risk to these sizes. Most large (over a kilometre in diameter) near-Earth asteroids are now known, but recognition that airbursts (or fireballs resulting from nuclear-weapon-sized detonations of meteoroids in the atmosphere) have the potential to do greater damage1 than previously thought has shifted an increasing portion of the residual impact risk (the risk of impact from an unknown object) to smaller objects2. Above the threshold size of impactor at which the atmosphere absorbs sufficient energy to prevent a ground impact, most of the damage is thought to be caused by the airburst shock wave3, but owing to lack of observations this is uncertain4,5. Here we report an analysis of the damage from the airburst of an asteroid about 19 metres (17 to 20 metres) in diameter southeast of Chelyabinsk, Russia, on 15 February 2013, estimated to have an energy equivalent of approximately 500 (±100) kilotons of trinitrotoluene (TNT, where 1 kiloton of TNT = 4.185×1012 joules). We show that a widely referenced technique4,5,6 of estimating airburst damage does not reproduce the observations, and that the mathematical relations7 based on the effects of nuclear weapons—almost always used with this technique—overestimate blast damage. This suggests that earlier damage estimates5,6 near the threshold impactor size are too high. We performed a global survey of airbursts of a kiloton or more (including Chelyabinsk), and find that the number of impactors with diameters of tens of metres may be an order of magnitude higher than estimates based on other techniques8,9. This suggests a non-equilibrium (if the population were in a long-term collisional steady state the size-frequency distribution would either follow a single power law or there must be a size-dependent bias in other surveys) in the near-Earth asteroid population for objects 10 to 50 metres in diameter, and shifts more of the residual impact risk to these sizes. |
| Databáze: | OpenAIRE |
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