普特英语听力mp3下载文本

普特英语听力mp3下载文本Saving the World from Asteroids

Okay, so there’s an asteroid heading toward the Earth. What do we do? Does our future really rest in the hands of Hollywood, Bruce Willis and a ragtag team of miners like in the movie Armageddon?

Early Warning

Sure, we could wait until danger is imminent and then hope that a well placed nuclear explosion would shatter or deflect the monster asteroid threatening humanity, but is this our only option? The answer is that it depends on how big the asteroid is, how far away it is, and How much time we have before impact?

Because there’s lots of space debris out there, odds are that the threatening object won’t be one of the giant Earth-destroying asteroids that NASA is already tracking, but a smaller meteoroid capable of causing regional devastation.

With enough warning, though, we could crash a robotic

spacecraft into the object and change its trajectory so that it’ll sail by Earth. We know we have the technology for this, because NASA has already successfully rammed a spacecraft into a comet to study the comet’s composition.

Deflection

There are also rare instances when space objects pass close by several years before returning on a collision course with Earth. Here even a tiny change in trajectory during the first pass would result in big payoff later. In these cases, we could use a spacecraft’s mass and gravitational field to nudge the space object off course without shattering it and creating potentially dangerous fragments.

Obviously, early warning is key, which is why NASA has issued a grand challenge to scientists in various disciplines, institutions and agencies to work together to uncover ways of detecting, characterizing and interacting with asteroids. Because when it comes to the future of the Earth, Bruce Willis can only do so much.

从小行星手里拯救世界

我们来假设，有颗小行星要撞地球啦，我们怎么办呢？难道真要想好莱坞电影《世界末日》里演的似的，把未来交到布鲁斯·威利斯和他那帮乌合之众手里？

早期预警

我们当然也能听任危机发展下去，在最后关头期待一枚核弹把带有毁灭威力的小行星击碎或者打偏。不过这难道是人类的选择？这个嘛，要看这颗小行星有多大，离地球有多远，我们有多少危机应对时间啦。

足以毁灭地球的小行星早已上了NASA的定位追踪名单。但宇宙里到处是太空垃圾，很可能没等那些小行星威胁到地球，一些更小的流星就已足以造成地域性灾难了。

不过，有了充足的预警，我们可以发射一些无人太空飞行器，把这些小天体撞离原定轨道。这种技术早就有了，NASA就曾把一架飞行器撞向颗彗星，用以研究彗星的成分。

轨道偏转

也有一种很少见的情况：一些天体早先只是擦过近地轨道，数年后飞回来时，却可能撞上地球。天体轨道极细微的变化都可能导致今后的大灾难。这种情况下，利用太空飞行器的质量和重力场，能将致命天体引偏些。用不着击碎它，这样也就不会产生可能威胁到地球安全的一堆碎片了。

显然，早期预警是关键。这也是为什么NASA给学界和各大相关机构出了个大挑战，让大家联合起来，预先测算分析和处理各种小行星的运行情况。因为一旦真的等到灾难临头，布鲁斯·威利斯可救不了人类。