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$ E# }+ b# _* A& k& p( gThe fireball that streaked across the skies above 3 @1 B" U6 [0 p+ ]; d- y+ f! C
Chelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth
$ q' q9 m/ c& k& @3 {8 { k$ Vof information. Two papers in this issue present detailed reconstructions of the
2 k3 \. |8 q2 [4 v' s# BChelyabinsk event. From an analysis of videos, Ji?í Borovi?ka et al. determined 7 ]3 ^/ }# [( [# S6 \. Z
the trajectory and velocity of the superbolide with high precision. Its orbit
@/ X7 O; W8 s/ \was similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43), 2 p' j- Y' ^8 w9 g
suggesting that the two bodies may be part of the same asteroid family. And they + m0 O" V/ k$ \
show that it broke into small pieces between the altitudes of 45 and 30 ! I+ W7 _) J1 @. v
kilometres. In the companion paper, Peter Brown et al. analysed the damage 5 _5 s# J! h6 f' D2 d
caused by the airburst which they estimate was equivalent in energy to the
5 @# Z3 w2 M" f! ~: b$ Ddetonation of 400 to 600 kilotons of TNT. They suggest that the number of
/ ^$ X; r! q* i/ {1 H0 Limpactors with diameters of tens of metres was an order of magnitude higher than , L/ c& @7 ~' r8 G8 r: _' {# z) A
current estimates, shifting much of the residual impact risk to these sizes. On + t! `/ v0 M3 ?& J* y- X5 X& v, X3 z
the cover, a 3D simulation by Mark Boslough using CTH code on Sandia National
9 [5 L0 j& d8 BLaboratories' Red Sky supercomputer, rendered by Brad Carvey using Houdini FX & g; R- w+ _5 i/ X) R* Z% ~
and LightWave; background photo by Olga Kluglova, go.nature.com/wxuV58.) W4 x% J: Y& L: k" U- F" Y4 v
8 W$ v+ g) `$ U9 Z' E7 L |
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发表于 2013-11-17 23:43
发表于 2013-11-18 08:19
