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The fireball that streaked across the skies above
5 }8 a1 l4 M. L5 q- Q3 @9 ^Chelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth
* R! h, Q# b% S4 w2 \2 ]7 H( y+ ~of information. Two papers in this issue present detailed reconstructions of the
1 M% C" Q5 ~% XChelyabinsk event. From an analysis of videos, Ji?í Borovi?ka et al. determined
/ g2 I9 f1 {$ _$ uthe trajectory and velocity of the superbolide with high precision. Its orbit
% B3 r* X" U! t0 ewas similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43),
: C( l1 ?8 p3 F L) j, ~suggesting that the two bodies may be part of the same asteroid family. And they
# D) O4 l6 P0 q9 W3 s I% M) _5 d+ Qshow that it broke into small pieces between the altitudes of 45 and 30 0 v( M, X4 ^7 y; N+ O/ G, l* c
kilometres. In the companion paper, Peter Brown et al. analysed the damage 8 l! g1 H0 K- Z2 A) s6 Y
caused by the airburst which they estimate was equivalent in energy to the
& _/ T7 C1 \( z$ E' n0 Wdetonation of 400 to 600 kilotons of TNT. They suggest that the number of
. e$ S. G0 h8 {# dimpactors with diameters of tens of metres was an order of magnitude higher than % r+ z k* F' C$ |7 Q
current estimates, shifting much of the residual impact risk to these sizes. On 6 u% e. C" Q8 f* g2 l
the cover, a 3D simulation by Mark Boslough using CTH code on Sandia National 8 [8 @3 ~6 C1 z! x
Laboratories' Red Sky supercomputer, rendered by Brad Carvey using Houdini FX
+ ^# `. P5 e( q) y: b: h4 U1 Oand LightWave; background photo by Olga Kluglova, go.nature.com/wxuV58.
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发表于 2013-11-17 23:43
发表于 2013-11-18 08:19
