2013年11月14日 Nature

nero1981

' y; c& U# `* q; V! V6 I) `The fireball that streaked across the skies above
  `2 ^0 j+ d5 `( H! J6 {Chelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth
( E' p7 `! E; S& N% s% Cof information. Two papers in this issue present detailed reconstructions of the # y$ a3 ~0 ]4 [" |* W. Y+ m' p
Chelyabinsk event. From an analysis of videos, Ji?í Borovi?ka et al. determined 7 \; k8 g, F) c8 q
the trajectory and velocity of the superbolide with high precision. Its orbit $ O2 m: n' I& D! i+ [
was similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43),   u) f3 v; E* F4 a# U" H
suggesting that the two bodies may be part of the same asteroid family. And they
6 N* u& K  G, S, Fshow that it broke into small pieces between the altitudes of 45 and 30 8 q( f- F0 o$ z' l# w3 P$ x  R
kilometres. In the companion paper, Peter Brown et al. analysed the damage 1 g/ n% u4 G! ?1 U
caused by the airburst which they estimate was equivalent in energy to the
  c; P7 }6 {% J. C5 y2 I8 U& h+ {detonation of 400 to 600 kilotons of TNT. They suggest that the number of 9 M8 L- {- E& X( l
impactors with diameters of tens of metres was an order of magnitude higher than 2 v7 M; M8 F+ X. |) J# I8 t
current estimates, shifting much of the residual impact risk to these sizes. On
* g1 f% e' f; ]; d5 b6 N+ ], k$ nthe cover, a 3D simulation by Mark Boslough using CTH code on Sandia National , z$ O2 x* c1 @6 ~2 T
Laboratories' Red Sky supercomputer, rendered by Brad Carvey using Houdini FX - ?2 R' H5 B- R9 l" N
and LightWave; background photo by Olga Kluglova, go.nature.com/wxuV58.
, }9 ?: b$ J3 p) G) l
# ^/ `& N  w( I) t& I5 V, \- m0 n

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