英语听力：探索发现 2014-06-18 BBC 地平线：陨石的真相-16

 Most of the damage from an explosion like this is actually the blast wave. It’s the very high winds. Mark created a simulation to see what size an asteroid¹ would need to be to be able to generate such destructive power. 

 

In this simulation I include more of the physics to be more realistic. We can see that the main shockwave doesn’t come out of the point of the explosion, but it comes out of the point where the fireball descends² to. So by the time the shockwave gets to the ground, it’s much stronger than it would otherwise be. And there’s more damage on the ground because the destructive power was carried downward. 

 

Based on Mark’s calculations, the devastation³ at Tunguska could have been caused by an asteroid, perhaps as small as 30 to 50 metres in diameter, and this carries a worrying implication. Smaller asteroids⁴ are more dangerous than we used to think and because there are so many more smaller asteroids than bigger asteroids we need to take that risk more seriously than we used to. 

 

The lesson of Tunguska helps explain why in Chelyabinsk there’s so much damage, but very little meteorite⁵ to be found. 

 

If we go back to the video footage and we see the object coming in when it’s in the high atmosphere, it suffers very little effect, but just here you get this huge flare-up and that’s because the atmosphere has become so dense⁶ that it’s almost impossible for it to push through any more. And basically something’s got to give and the asteroid gives, and it basically just breaks apart in a huge catastrophic fragmentation event. And that is what creates a shockwave which we hear as this sonic boom. 

 

1 asteroid   

n.小行星；海盘车(动物)

参考例句：

• Astronomers have yet to witness an asteroid impact with another planet.天文学家还没有目击过小行星撞击其它行星。
• It's very unlikely that an asteroid will crash into Earth but the danger exists.小行星撞地球的可能性很小，但这样的危险还是存在的。

2 descends   

v.下来( descend的第三人称单数 )；下去；下降；下斜

参考例句：

• This festival descends from a religious rite. 这个节日起源于宗教仪式。 来自《简明英汉词典》
• The path descends steeply to the village. 小路陡直而下直到村子。 来自《简明英汉词典》

3 devastation   

n.毁坏；荒废；极度震惊或悲伤

参考例句：

• The bomb caused widespread devastation. 炸弹造成大面积破坏。
• There was devastation on every side. 到处都是破坏的创伤。 来自《简明英汉词典》

4 asteroids   

n.小行星( asteroid的名词复数 )；海盘车，海星

参考例句：

• Asteroids,also known as "minor planets",are numerous in the outer space. 小行星，亦称为“小型行星”，在外太空中不计其数。
• Most stars probably have their quota of planets, meteorids, comets, and asteroids. 多数恒星也许还拥有若干行星、流星、彗星和小行星。

5 meteorite   

n.陨石；流星

参考例句：

• The meteorite in Jilin Exhibition Hall is believed to be the largest in the world.吉林展览馆的陨石被认为是世界上最大的。
• The famous Murchison meteorite smashed into the Australian ground in 1969.1969年著名的默奇森陨石轰然坠落在澳大利亚。

6 dense   

a.密集的，稠密的，浓密的；密度大的

参考例句：

• The general ambushed his troops in the dense woods. 将军把部队埋伏在浓密的树林里。
• The path was completely covered by the dense foliage. 小路被树叶厚厚地盖了一层。