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2 v6 U8 z; n$ b; D- D% ^: qThe fireball that streaked across the skies above ! A2 n" d: M9 x/ {5 c! c
Chelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth
( t0 W8 \* \* P4 q: e2 {of information. Two papers in this issue present detailed reconstructions of the j1 Z+ C: K3 s' J2 E: n
Chelyabinsk event. From an analysis of videos, Ji?í Borovi?ka et al. determined + U4 x" T9 K9 n( v' j) s" k: a
the trajectory and velocity of the superbolide with high precision. Its orbit
7 p6 _* a- E. U. c; n: k7 |was similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43),
2 c0 Y. e. V% D2 c ]2 xsuggesting that the two bodies may be part of the same asteroid family. And they
# ^9 D `" h! O" E; Cshow that it broke into small pieces between the altitudes of 45 and 30
( a- V/ V# H3 A* X& L% pkilometres. In the companion paper, Peter Brown et al. analysed the damage
4 `! k( V* Z2 Q& q8 f w5 zcaused by the airburst which they estimate was equivalent in energy to the
4 c ^ X0 }; ~detonation of 400 to 600 kilotons of TNT. They suggest that the number of + ? G# A7 Z: `+ b; F
impactors with diameters of tens of metres was an order of magnitude higher than 8 }* c" u! S& A6 z+ x4 p# Q
current estimates, shifting much of the residual impact risk to these sizes. On 5 x' m- G$ `) b
the cover, a 3D simulation by Mark Boslough using CTH code on Sandia National
5 f Y* x, [7 cLaboratories' Red Sky supercomputer, rendered by Brad Carvey using Houdini FX
4 p! r/ x/ \2 P3 P& D: Sand 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
