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The fireball that streaked across the skies above ' r) E6 _3 X1 N; R1 _4 dChelyabinsk in Russia on 15 February 2013 is providing astronomers with a wealth + Z- c) v. Y2 ~of information. Two papers in this issue present detailed reconstructions of the 6 C+ [' @$ }, O( o
Chelyabinsk event. From an analysis of videos, Ji?í Borovi?ka et al. determined 4 P4 ^' [7 j; \/ A7 X9 \, `% a* s- x
the trajectory and velocity of the superbolide with high precision. Its orbit # H/ _% i8 y4 x4 R
was similar to that of the 2-kilometre-diameter asteroid 86039 (1999 NC43), ! _: I- r5 l6 h: f! s0 Isuggesting that the two bodies may be part of the same asteroid family. And they ! C* X, T* r& r' w1 a7 [$ Tshow that it broke into small pieces between the altitudes of 45 and 30 " s+ `' M: s; o# fkilometres. In the companion paper, Peter Brown et al. analysed the damage & J. ^) _4 a+ i4 v* u Ycaused by the airburst which they estimate was equivalent in energy to the % v5 e: V6 L$ n# ]0 t$ \detonation of 400 to 600 kilotons of TNT. They suggest that the number of $ B+ d& e7 `' c
impactors with diameters of tens of metres was an order of magnitude higher than / g W1 m6 F3 C1 ^& b3 `1 c
current estimates, shifting much of the residual impact risk to these sizes. On - L2 ?5 M0 q: x, m" Ithe cover, a 3D simulation by Mark Boslough using CTH code on Sandia National , F7 ~) Q: j5 H2 R! O& |/ @+ I7 @Laboratories' Red Sky supercomputer, rendered by Brad Carvey using Houdini FX 6 R3 |3 W T* i$ U
and LightWave; background photo by Olga Kluglova, go.nature.com/wxuV58. + s, m" \4 e# Q/ \ : v( \7 b6 e- B+ V作者: 懵懂干细胞 时间: 2013-11-18 08:19
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