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' e4 l7 N7 ?0 e; C! \The fireball that streaked across the skies above ! W" g1 q' G( z, i2 j7 q
Chelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth
/ M! d" |( ] V fof information. Two papers in this issue present detailed reconstructions of the k! @; h4 Q: O# q- c
Chelyabinsk event. From an analysis of videos, Ji?í Borovi?ka et al. determined 6 m7 q2 P5 ?0 L, N+ ]
the trajectory and velocity of the superbolide with high precision. Its orbit
- A9 x: b6 o( f* D8 @3 iwas similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43), $ j. g4 s1 {7 q, C. {
suggesting that the two bodies may be part of the same asteroid family. And they
6 Z/ m2 k) d9 l# R& }/ e& _) l* a3 Cshow that it broke into small pieces between the altitudes of 45 and 30
& Y7 L( `8 R" S7 @8 f5 Skilometres. In the companion paper, Peter Brown et al. analysed the damage # w* a1 }6 P1 i9 n& n# e
caused by the airburst which they estimate was equivalent in energy to the
* F- Z2 r) D5 m0 J* R: w* Tdetonation of 400 to 600 kilotons of TNT. They suggest that the number of
% y ?+ W, `8 U+ ?impactors with diameters of tens of metres was an order of magnitude higher than
# c5 P& G, t9 Z; o) Xcurrent estimates, shifting much of the residual impact risk to these sizes. On
8 a4 u* W! ^# s& Z" jthe cover, a 3D simulation by Mark Boslough using CTH code on Sandia National
) l4 i+ A! E# \' T0 w+ xLaboratories' Red Sky supercomputer, rendered by Brad Carvey using Houdini FX 9 a3 {3 [4 M0 [
and LightWave; background photo by Olga Kluglova, go.nature.com/wxuV58.
9 B' [, U/ P% G1 J; y* a1 X) ^& z( H" I9 L, ^
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发表于 2013-11-17 23:43
发表于 2013-11-18 08:19
