好英语网彗星撞地球：我们能否预先发现带来毁灭的小行星？
These scientists are on a quest to spot asteroids before they smash into Earth.
我们的任务是在小行星撞击地球之前发现它。
For five long days, a team of meteorite hunters had tussled with thorn bushes and trudged through thick grass in the middle of Botswana. They knew roughly where they should be looking – within a 200 sq km area – but the fragment was likely tiny. Who knows if it had been buried, or even blown away by the wind.
一队陨石猎人在博茨瓦纳（Botswana）中部灌木林和茂密草丛中跋涉了整整五天。他们知道大概的搜索范围是方圆200平方公里，但碎片可能极小，谁知道是不是被埋在地下了或是被风吹走了。
And then. There it was, a tiny chunk of black, dusty stone that came from outer space. About a month earlier, a team of astronomers had predicted in what part of the world meteorites from a particular asteroid would fall. That asteroid, named 2018 LA, exploded in the night-time sky in Botswana several hours after it was seen hurtling towards our plant.
最后，他们真的找到了这颗小石头。这颗落满灰尘的黑色石头来自外太空。大约一个月前，一组天文学家曾预测，来自特定小行星的陨石将坠落到地球某处。人们观测到这颗名为“2018 LA”的小行星正冲向地球。数小时后，它便在博茨瓦纳的夜空中爆炸。
Finding the fragment proved the astronomers right – and it was only the second time in history that fragments of a meteorite had been found from an asteroid previously observed in space.
陨石碎片证明了天文学家的预测是正确的，这也是人类历史上第二次找到被观测到的小行星陨石碎片。
One of the teams that contributed to this fantastic find is hoping that their system of telescopes can one day warn people on Earth in advance of a bigger, potentially fatal, impact. But how will they do it?
天文学家们希望通过望远镜能发现更严重、有可能致命的陨石撞击，并在事先发出警告。但他们怎么做到这一点？
While still in space, 2018 LA was first spotted by the Catalina Sky Survey, a Nasa-funded project. But it was then also observed by the Asteroid Terrestrial-Impact Last Alert System (Atlas) at the University of Hawaii. Atlas is a system of telescopes that has been designed with one ultimate goal in mind: save earthlings from giant space rocks.
NASA资助的“卡特琳娜天空调查”项目（Catalina Sky Survey）首次发现了当时还在太空中的“2018 LA”。随后夏威夷大学的“阿特拉斯小行星撞击陆地最后预警系统”（Asteroid Terrestrial-Impact Last Alert System, Atlas）也观测到了这一现象。阿特拉斯（Atlas）是一套望远镜系统，终极目标是避免地球遭到巨大的太空岩石的撞击。
It was set up by John Tonry, an astronomer. He was inspired to start the project years ago after constantly hearing that the chances of a dangerous asteroid hitting Earth were very low – once every millennium or so.
它由天文学家托尼（John Tonry）建立。几年前，他总是听说小行星撞击地球的几率非常低，大约每千年才会发生一次。托尼因此有了这个想法。
“It really bugged me that that number was always handed out without any uncertainty and the actual, most recent event of that type was only 100 years ago,” he explains.
他解释说：“人们总是提到这个概率，既没有证据支持，也不可靠，这让我很困扰，而且最近发生的这类事件也不过是100年前的事。”
Tonry is referring to the 1908 Tunguska event in Siberia, in which an asteroid exploded in the atmosphere, creating a 50-100m wide fireball and flattening about 80 million trees. Reportedly, one person died in the incident. Had the impact site been a more populated area, the effects would have been horrific.
托尼指的是1908年西伯利亚的通古斯卡事件（Tunguska）。当时一颗小行星在大气中爆炸，形成了一个50至100米宽的火球，压倒了大约8000万棵树。据报道，有一人在事故中死亡。如果撞击地点是人口更密集的地区，后果将不可设想。
Atlas consists of two telescopes in Hawaii, though Tonry is currently working with colleagues on setting up a third in South Africa, to observe the sky in the southern hemisphere. A fourth telescope has also been funded. Once the full system gets going, Tonry hopes it will offer us a good chance of spotting a major potential impact and, if needs be, it could provide enough notice to evacuate the predicted impact site.
阿特拉斯望远镜系统由夏威夷的两台望远镜组成，不过托尼目前正与同事们在南非建立第三台望远镜，用于观察南半球的天空。第四架望远镜也得到了资助。一旦整个系统启动，托尼希望它帮助我们预测主要的撞击，如果需要的话，它还可以发布通知以疏散受影响区域的人员。
Thanks to this summer’s fragment discovery in Botswana, we know Atlas can get it right. And pinpointing the landing place of 2018 LA was all the more impressive since it was such a small asteroid, less than 2m across.
通过今年夏天在博茨瓦纳发现的碎片，我们确认阿特拉斯确实是准确的。“2018 LA”是一颗直径不到2米的小行星，能够确定其落地点很了不起。
“It’s a very good initiative, the Atlas system” says Clemens Rumpf, a visiting researcher at the University of Southampton who specialises in the study of asteroids.
“阿特拉斯系统是一个非常好的方案，”南安普敦大学专门研究小行星的访问研究员拉姆夫（Clemens Rumpf）说。
“Even today we miss a lot of asteroids that are potentially dangerous.”
“即使在今天，我们仍然对很多有潜在威胁的小行星一无所知。”
The space around Earth is full of rocks. Atlas’s job is to pick out the ones that might threaten us. Tonry explains that in a single night of observations, he and his team might detect about a million objects. A lot of those will be stars or exploding stars (supernovae), or known asteroids on safe trajectories. There might be just ten or twenty that are new to us, and not necessarily any that are dangerous.
地球周围的空间遍布岩石。阿特拉斯的工作是找出那些可能威胁我们的岩石。托尼解释说，他和他的团队一晚上可能会探测到大约100万个。其中许多将变成恒星或是正在爆炸的恒星（超新星），又或是已知的在安全轨道上运行的小行星。对我们来说，可能只有10到20个是新的，而不一定是危险的。
If something headed for Earth does crop up, Atlas can post an update to its web pages. Astronomers at institutions like Nasa or the International Astronomical Union’s Minor Planet Center have automated scripts that scour such web-pages for new information. This is how they know as soon as a possible discovery has been made. Astronomers can then begin plotting trajectories and predicting impact sites.
如果有什么东西突然朝地球飞过来，阿特拉斯会在其网站上发布更新。美国国家航空航天局和国际天文学联合会（International Astronomical Union）下属的小行星中心（Minor Planet Center）等机构的天文学家已经编写了自动程序脚本，可以在这些网页上发布新的信息。凭借这种方式，他们可以及时了解新进展，然后就可以开始绘制轨道和预测撞击地球的地点。
Rumpf points out that some larger asteroids are in a regular orbit around the sun, usually an oval-shaped path that may or may not intersect with Earth at some point in the future. Possible future impacts of such asteroids are easier to predict – but not all space rocks play nice.
拉姆夫指出，一些较大的小行星正处于围绕太阳的正常轨道上。这些轨道通常是一个椭圆形，并且在未来某一时刻可能与地球相交，也可能不相交。这些小行星未来潜在的影响更容易预测，但并非所有的太空岩石都是这样。
“[Some] are on irregular orbits because they are not bound by the sun,” explains Rumpf. “They kind of come out of nowhere.”
“有一些处于不规则轨道上，因为它们不受太阳引力的约束，”拉姆夫解释说。“这些就不知会从哪里冒出来。”
Systems like Atlas might be particularly useful, in theory, at spotting those just in time.
从理论上讲，像阿特拉斯这样的系统在及时发现这些岩石方面可能特别有用。
By studying how light reflects off different kinds of rocks, such as those with higher metal content and so on, scientists can then make predictions about asteroids flying towards Earth based on the light they themselves reflect, says Alessondra Springmann, a planetary radar astronomer at the University of Arizona.
亚利桑那大学的行星雷达天文学家斯普林曼（Alessondra Springmann）说，通过研究光在不同种类岩石上的反射情况，比如那些金属含量更高的岩石等等，科学家就可以根据小行星反射的光来预测小行星飞向地球的情况。
“If the asteroid comes close enough you can use radar – if you have shape, volume and composition then you can perhaps work out the density,” she adds.
“如果小行星离得足够近，你可以使用雷达，如果了解了行星的形状、体积和组成等数据，那么也许可以计算出密度，”她补充说。
That can help predict what kind of explosion a large asteroid might make as it enters Earth’s atmosphere. The more solid and the heavier it is, the worse the news could be for mankind.
这有助于预测一颗大型行星进入地球大气层时可能会发生什么样的爆炸。对人类来说，行星越结实、越沉重，结果越糟糕。
What if we find an asteroid so big that it could threaten thousands or millions of lives? Or throw up so much debris into our atmosphere that the climate would be damaged for a very long time?
如果我们发现了一颗可能会威胁到成千上万甚至上百万人生命的大型行星，该怎么办？或者由于撞击地球产生大量烟尘，地球气候受到长时间破坏，该怎么办？
Ideally, we’d spot such a monster long before it arrived, which might give us time to defend ourselves. Springmann notes that there are a couple of ideas for how to do this – including launching a “gravitational tractor”. This would involve blasting a spacecraft towards the asteroid and positioning it close enough that the, albeit tiny, gravitational pull of the craft could steer the asteroid off-course.
理想情况下，我们应该在这种怪物到来之前很久就发现它，这样我们就有足够的时间来保护自己。斯普林曼指出，有几个解决方案，包括发射一个“引力牵引器”，比如向小行星发射一艘宇宙飞船，并将其定位在足够靠近小行星的位置，使飞船的引力（尽管很小）能够引导小行星偏离轨道。
“If you don’t have a lot of warning, the last ditch effort is to send a kinetic impactor,” she says, before clarifying: “a bomb”.
她说：“如果没有足够的预警，使用动能冲击是最后一道防线。”其实就是一颗“炸弹”，她解释道。
If we do ever get the chance to shatter a life-threatening space boulder, it’ll be thanks to observations made by scientists here on Earth that tell to some degree of confidence us how big it is, how fast it’s moving – and how likely it is to kill us all.
如果我们有机会粉碎危及生命的大石头，前提一定是因为科学家们能够准确预测到它的大小、移动速度以及毁灭人类的可能性。