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The fireball that streaked across the skies above
7 s( \3 N: Z/ o- K5 W$ A' FChelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth % t+ Y* y( s& I5 n5 x
of information. Two papers in this issue present detailed reconstructions of the 5 ^8 }9 W8 K8 J- K$ }4 x* m* P
Chelyabinsk event. From an analysis of videos, Ji?í Borovi?ka et al. determined # j/ A% C2 x1 r
the trajectory and velocity of the superbolide with high precision. Its orbit 0 Q* S- j% c* \8 I8 C2 m2 ^. P5 R
was similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43), ) J" C% ^7 H1 ]3 E6 {0 o! s9 ^
suggesting that the two bodies may be part of the same asteroid family. And they
0 L; w5 \7 E/ ~/ R2 U& `/ C; {9 C3 fshow that it broke into small pieces between the altitudes of 45 and 30 " I% _0 j- R5 R1 F
kilometres. In the companion paper, Peter Brown et al. analysed the damage : N) T7 S, }0 L2 b( t3 a9 u
caused by the airburst which they estimate was equivalent in energy to the
5 D0 U5 q8 E0 n m& G" ndetonation of 400 to 600 kilotons of TNT. They suggest that the number of
! v0 ? Z# E) F1 dimpactors with diameters of tens of metres was an order of magnitude higher than
+ r8 `0 X+ y" }. v6 s( \; ^current estimates, shifting much of the residual impact risk to these sizes. On
" P+ F0 {$ l B; cthe cover, a 3D simulation by Mark Boslough using CTH code on Sandia National
' O9 F4 B4 z4 m X h$ U0 e) XLaboratories' Red Sky supercomputer, rendered by Brad Carvey using Houdini FX
( n+ G2 Q% r1 {$ rand LightWave; background photo by Olga Kluglova, go.nature.com/wxuV58.+ }" F: }$ \' M8 O0 A% Q
3 q/ g3 A$ E, U+ U& A8 |' u+ M
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发表于 2013-11-17 23:43
发表于 2013-11-18 08:19
