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The fireball that streaked across the skies above
" p+ B9 Z e" S4 o/ x5 Z& LChelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth 3 D0 j- o! S# u# V7 r; b6 L
of information. Two papers in this issue present detailed reconstructions of the
* D4 E, o4 ^. J" f) { A- Y6 kChelyabinsk event. From an analysis of videos, Ji?í Borovi?ka et al. determined 7 O" J. ~0 ] s2 |4 x
the trajectory and velocity of the superbolide with high precision. Its orbit
1 J1 s% V' ~: [" E$ s. p3 Owas similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43), * U' G1 w. `9 d+ P' {. V L; h
suggesting that the two bodies may be part of the same asteroid family. And they 3 ?- M* h$ a+ a" I$ A
show that it broke into small pieces between the altitudes of 45 and 30 6 V/ k, _- \; k4 f# Z. U- R1 z
kilometres. In the companion paper, Peter Brown et al. analysed the damage
6 i8 h8 F$ U& @3 L" s5 ?caused by the airburst which they estimate was equivalent in energy to the . Q2 b- f4 \) K% P3 s, p" J
detonation of 400 to 600 kilotons of TNT. They suggest that the number of 4 x. w) Z! i# n% `% n
impactors with diameters of tens of metres was an order of magnitude higher than 9 Q/ \/ x7 G _6 ?
current estimates, shifting much of the residual impact risk to these sizes. On
+ Z0 ?3 t ]! A& O$ [/ l Mthe cover, a 3D simulation by Mark Boslough using CTH code on Sandia National
8 }! u' C* | U2 s, Q" qLaboratories' Red Sky supercomputer, rendered by Brad Carvey using Houdini FX
0 v2 @2 e$ J2 t3 E' eand LightWave; background photo by Olga Kluglova, go.nature.com/wxuV58." s; z- M' p! M6 P
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发表于 2013-11-17 23:43
发表于 2013-11-18 08:19
