2013年11月14日 Nature

nero1981

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The fireball that streaked across the skies above
$ j3 x* \+ o& ~! S! P# S  SChelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth 3 Y" F3 J! L$ x- k1 v5 \& U$ @
of information. Two papers in this issue present detailed reconstructions of the
* u4 ~) e8 P6 wChelyabinsk event. From an analysis of videos, Ji?í Borovi?ka et al. determined
5 ?1 z# ^% }9 \" F- N; ?5 tthe trajectory and velocity of the superbolide with high precision. Its orbit # D1 o2 Q, V- c$ W
was similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43),
% j9 M0 T# b. \, Vsuggesting that the two bodies may be part of the same asteroid family. And they
1 ]  A( ^! b6 C1 h2 o( Tshow that it broke into small pieces between the altitudes of 45 and 30 7 A" {5 l: s( j' u- e, p1 h
kilometres. In the companion paper, Peter Brown et al. analysed the damage 2 l% b7 k7 p% b- k# b- o" e, |8 V* h
caused by the airburst which they estimate was equivalent in energy to the
. o/ f5 d: J' O, \0 X) ndetonation of 400 to 600 kilotons of TNT. They suggest that the number of 2 N; v) \' c! C8 \
impactors with diameters of tens of metres was an order of magnitude higher than
  o5 F' p9 D. {1 y8 Pcurrent estimates, shifting much of the residual impact risk to these sizes. On
/ I; M" i+ K9 i: l4 [% Tthe cover, a 3D simulation by Mark Boslough using CTH code on Sandia National
( ?+ z7 B2 y% T& C. GLaboratories' Red Sky supercomputer, rendered by Brad Carvey using Houdini FX 9 K$ o5 A& p' c6 }0 M
and LightWave; background photo by Olga Kluglova, go.nature.com/wxuV58.4 k- `5 v( l" H+ y/ c6 h, D. x

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