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The fireball that streaked across the skies above $ `: E4 Y" T8 Z) N3 [
Chelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth . d/ @% m2 o7 L/ h) m
of information. Two papers in this issue present detailed reconstructions of the - h$ D* e& v1 Y$ {
Chelyabinsk event. From an analysis of videos, Ji?í Borovi?ka et al. determined 4 @: S+ p/ L, L5 E2 g f
the trajectory and velocity of the superbolide with high precision. Its orbit
7 x5 c& r8 m+ w1 @7 V# ]# ?; Pwas similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43), 9 \1 c: H7 L" `4 ]* F& [
suggesting that the two bodies may be part of the same asteroid family. And they
5 |( Z' U7 q! p: [, D- W$ ~# `show that it broke into small pieces between the altitudes of 45 and 30
/ s* O! R" R$ h& u* zkilometres. In the companion paper, Peter Brown et al. analysed the damage * K& {% `$ S0 u0 M
caused by the airburst which they estimate was equivalent in energy to the / f* z2 F0 w) Z( z, ~9 G6 U) w3 h% x
detonation of 400 to 600 kilotons of TNT. They suggest that the number of 0 [4 l# D+ j. g' n1 a( ~& o
impactors with diameters of tens of metres was an order of magnitude higher than 9 r8 d b) L v N& S$ Z7 H4 c: v
current estimates, shifting much of the residual impact risk to these sizes. On / p- K6 k, T2 ?/ N8 W
the cover, a 3D simulation by Mark Boslough using CTH code on Sandia National 4 I$ {5 p: Q) J" X3 i1 b
Laboratories' Red Sky supercomputer, rendered by Brad Carvey using Houdini FX / N+ f( `- k! M3 q3 u
and LightWave; background photo by Olga Kluglova, go.nature.com/wxuV58.
+ m" h, [- p A9 |* F. Z7 d$ {6 C- K& k \# e
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发表于 2013-11-17 23:43
发表于 2013-11-18 08:19
