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9 }: e6 W, m0 p) O% f3 dThe fireball that streaked across the skies above " K/ P/ {$ c% n% i+ J
Chelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth
# E; J% Q. \" |/ `, T1 h( hof information. Two papers in this issue present detailed reconstructions of the
m% m, u! X# mChelyabinsk event. From an analysis of videos, Ji?í Borovi?ka et al. determined $ ?+ `/ G9 {! E1 D3 x
the trajectory and velocity of the superbolide with high precision. Its orbit
% ]! G2 c& r4 ?3 R. j, vwas similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43), 0 A( [7 b: W. O, a
suggesting that the two bodies may be part of the same asteroid family. And they
/ H' [9 _2 b" k" [& I# Cshow that it broke into small pieces between the altitudes of 45 and 30 2 x9 l0 @" K2 G$ T
kilometres. In the companion paper, Peter Brown et al. analysed the damage
$ J7 q3 Z) n. Q4 _; Hcaused by the airburst which they estimate was equivalent in energy to the
" q4 C. N" w- F2 ydetonation of 400 to 600 kilotons of TNT. They suggest that the number of * X% `( s( n+ ]; v0 R. i. @
impactors with diameters of tens of metres was an order of magnitude higher than
0 b. c# K) l7 P5 d- M8 Bcurrent estimates, shifting much of the residual impact risk to these sizes. On
) r+ u& f# r9 f$ O. u4 Y/ Othe cover, a 3D simulation by Mark Boslough using CTH code on Sandia National % D1 i$ A+ c4 @2 S7 V6 D; K5 `, o
Laboratories' Red Sky supercomputer, rendered by Brad Carvey using Houdini FX * Y: K8 {8 I. O, V% G2 H" {
and LightWave; background photo by Olga Kluglova, go.nature.com/wxuV58.' g1 W9 Z. g# g! p
* a" T: g6 C u
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发表于 2013-11-17 23:43
发表于 2013-11-18 08:19
