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.
從小行星手里拯救世界
我們來假設(shè)，有顆小行星要撞地球啦，我們怎么辦呢？難道真要想好萊塢電影《世界末日》里演的似的，把未來交到布魯斯·威利斯和他那幫烏合之眾手里？
早期預(yù)警
我們當(dāng)然也能聽任危機(jī)發(fā)展下去，在最后關(guān)頭期待一枚核彈把帶有毀滅威力的小行星擊碎或者打偏。不過這難道是人類的選擇？這個嘛，要看這顆小行星有多大，離地球有多遠(yuǎn)，我們有多少危機(jī)應(yīng)對時間啦。
足以毀滅地球的小行星早已上了NASA的定位追蹤名單。但宇宙里到處是太空垃圾，很可能沒等那些小行星威脅到地球，一些更小的流星就已足以造成地域性災(zāi)難了。
不過，有了充足的預(yù)警，我們可以發(fā)射一些無人太空飛行器，把這些小天體撞離原定軌道。這種技術(shù)早就有了，NASA就曾把一架飛行器撞向顆彗星，用以研究彗星的成分。
軌道偏轉(zhuǎn)
也有一種很少見的情況：一些天體早先只是擦過近地軌道，數(shù)年后飛回來時，卻可能撞上地球。天體軌道極細(xì)微的變化都可能導(dǎo)致今后的大災(zāi)難。這種情況下，利用太空飛行器的質(zhì)量和重力場，能將致命天體引偏些。用不著擊碎它，這樣也就不會產(chǎn)生可能威脅到地球安全的一堆碎片了。
顯然，早期預(yù)警是關(guān)鍵。這也是為什么NASA給學(xué)界和各大相關(guān)機(jī)構(gòu)出了個大挑戰(zhàn)，讓大家聯(lián)合起來，預(yù)先測算分析和處理各種小行星的運(yùn)行情況。因?yàn)橐坏┱娴牡鹊綖?zāi)難臨頭，布魯斯·威利斯可救不了人類。
