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The fireball that streaked across the skies above + [2 l* C" b/ h
Chelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth & s6 g2 A, t$ M
of information. Two papers in this issue present detailed reconstructions of the 1 k( X3 Y6 x/ R. N6 {
Chelyabinsk event. From an analysis of videos, Ji?í Borovi?ka et al. determined
$ M& t2 V" `' z1 }* p6 C, H$ L' Qthe trajectory and velocity of the superbolide with high precision. Its orbit
! o, I5 g3 x" z8 _! ]' o5 kwas similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43), 0 T5 O7 v' ~) s( g; B" b4 A
suggesting that the two bodies may be part of the same asteroid family. And they
* E# d0 Z$ \# _" _show that it broke into small pieces between the altitudes of 45 and 30 3 b) L0 T" ^- O+ f/ N! D
kilometres. In the companion paper, Peter Brown et al. analysed the damage
# H9 s, V$ f1 i: D+ ocaused by the airburst which they estimate was equivalent in energy to the 7 o/ k& H {# o# x+ }
detonation of 400 to 600 kilotons of TNT. They suggest that the number of * Z' \" n6 X% A6 T) w( M
impactors with diameters of tens of metres was an order of magnitude higher than
4 |! \7 |+ N5 p" T' wcurrent estimates, shifting much of the residual impact risk to these sizes. On
* F- A ^* V+ V$ u2 P+ H5 M" Bthe cover, a 3D simulation by Mark Boslough using CTH code on Sandia National $ h9 J, J d; u6 S
Laboratories' Red Sky supercomputer, rendered by Brad Carvey using Houdini FX
# ?$ m% f. A# X o' ^% t1 `* O7 u& 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
