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The fireball that streaked across the skies above
& P. P: z) [! a' W( r# `Chelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth 1 l( f2 c! z+ q& |# i1 G: c
of information. Two papers in this issue present detailed reconstructions of the
' N$ m1 ~) @: F; aChelyabinsk event. From an analysis of videos, Ji?í Borovi?ka et al. determined
* \5 p% ~3 y8 L3 Athe trajectory and velocity of the superbolide with high precision. Its orbit / C; r( z; P' `1 c
was similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43), 4 _7 h% C6 D; M$ c0 d
suggesting that the two bodies may be part of the same asteroid family. And they , D* c: P% k. |/ P& I- Q( J# n
show that it broke into small pieces between the altitudes of 45 and 30 1 Q& p% N# V% z3 ]" ^4 ]( ^
kilometres. In the companion paper, Peter Brown et al. analysed the damage - p" @' f+ p7 }* ~) C1 ?! |4 r( ~
caused by the airburst which they estimate was equivalent in energy to the
% g" p% h5 ?5 @2 Q, Pdetonation of 400 to 600 kilotons of TNT. They suggest that the number of
' e% p5 p. W; B4 E. l; j. Kimpactors with diameters of tens of metres was an order of magnitude higher than 6 r* z B: i, G# W5 B7 y& J
current estimates, shifting much of the residual impact risk to these sizes. On : }7 s( l4 d; s3 W1 h A
the cover, a 3D simulation by Mark Boslough using CTH code on Sandia National
4 [% a" E5 @ Y( `Laboratories' Red Sky supercomputer, rendered by Brad Carvey using Houdini FX ) o& p6 ^7 d' i4 A |- n0 F
and LightWave; background photo by Olga Kluglova, go.nature.com/wxuV58.1 a; {! e0 ~/ i# K! K
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发表于 2013-11-17 23:43
