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The fireball that streaked across the skies above
" L8 }( y; r# v& kChelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth ( m% J9 j8 a9 D! w
of information. Two papers in this issue present detailed reconstructions of the 7 Y0 ^$ _% h2 k: @* r) T
Chelyabinsk event. From an analysis of videos, Ji?í Borovi?ka et al. determined 7 ~, v' L8 q c1 S' y( ?/ n/ M7 S& c
the trajectory and velocity of the superbolide with high precision. Its orbit - D3 l: D/ `3 C; p# L1 {
was similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43),
) ]( P9 t$ d+ M# I5 Esuggesting that the two bodies may be part of the same asteroid family. And they
/ F& Q% L2 \5 [: Z: Wshow that it broke into small pieces between the altitudes of 45 and 30 ' {; j3 L- M: u, w+ t b, I( J" }
kilometres. In the companion paper, Peter Brown et al. analysed the damage 4 |& l+ q7 v3 Z
caused by the airburst which they estimate was equivalent in energy to the ) M2 c5 }% Y4 W
detonation of 400 to 600 kilotons of TNT. They suggest that the number of , [6 {& ]" Z' O+ Y& y% R
impactors with diameters of tens of metres was an order of magnitude higher than & H: J |, k( A7 D+ R" b- u$ U
current estimates, shifting much of the residual impact risk to these sizes. On & U$ `1 v, k0 Y5 G, V- F
the cover, a 3D simulation by Mark Boslough using CTH code on Sandia National
$ j/ o7 ]1 }( o: \- ?9 s7 n! W2 JLaboratories' Red Sky supercomputer, rendered by Brad Carvey using Houdini FX
5 H; \1 S' l9 V1 a' k( qand LightWave; background photo by Olga Kluglova, go.nature.com/wxuV58.
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发表于 2013-11-17 23:43
发表于 2013-11-18 08:19
