I am holding something remarkably old.
我手中拿的是一个非常古老的东西。
It is older than any human artifact, older than life on Earth, older than the continents and the oceans between them.
它比任何人造制品，比地球上任何生命，比任何陆地和大洋都要古老。
This was formed over four billion years ago in the earliest days of the solar system while the planets were still forming.
它是四十多亿年前形成的。那时还是太阳系的最早期，众星球还在形成。
This rusty lump of nickel and iron may not appear special, but when it is cut open...
这一块生锈的镍铁，看起来可能没有什么特别之处。但如果把它切开，
you can see that it is different from earthly metals.
你会发现它与地球的金属不同。
This pattern reveals metallic crystals that can only form out in space
它的纹路显示它是只能在太空中形成的金属晶体。
where molten metal can cool extremely slowly, a few degrees every million years.
在太空中，熔化了的金属，可以以极慢的速度冷却，每几百万年，只冷却几度。
This was once part of a much larger object, one of millions left over after the planets formed. We call these objects asteroids.
这是一个比它大很多的物体的一部分。星球形成后，它是数百万被遗落的物体之一。我们把这些物体叫做小行星。
Asteroids are our oldest and most numerous cosmic neighbors.
小行星是我们宇宙邻居里最古老和为数最多的。
This graphic shows near-Earth asteroids orbiting around the Sun,
这幅图像展示了靠近地球的小行星绕太阳运转，
shown in yellow, and swinging close to the Earth's orbit, shown in blue.
太阳是图中黄色的那个，它们活跃于地球绕行轨道附近，地球轨道是图中蓝色部分。
The sizes of the Earth, Sun and asteroids have been greatly exaggerated so you can see them clearly.
为了让大家看得清楚，图中的地球、太阳和小行星都被放大了很多倍。
Teams of scientists across the globe are searching for these objects,
世界各地的科学家团队都在寻找这些物体，
discovering new ones every day, steadily mapping near-Earth space.
他们每天发现新的小行星，逐渐绘制着近地空间的地图。
Much of this work is funded by NASA. I think of the search for these asteroids as a giant public works project,
这项工作大部分是由美国国家航空暨太空总署资助的。我觉得，搜寻小行星的工作，是极为浩大的公共工程项目，
but instead of building a highway, we're charting outer space, building an archive that will last for generations.
我们为太空制图，而不是在建高速公路，并建立着能够世代延续的档案。
These are the 1,556 near-Earth asteroids discovered just last year.
光是去年，科学家就发现了1556颗近地小行星。
And these are all of the known near-Earth asteroids, which at last count was 13,733.
图上的这些，是我们已知的全部近地小行星。根据最近的统计，总数是13733颗。
Each one has been imaged, cataloged and had its path around the Sun determined.
每一颗小行星，都已经被绘图和编入目录，它绕太阳运行的轨迹，也都已经被确定。
Although it varies from asteroid to asteroid, the paths of most asteroids can be predicted for dozens of years.
虽然每一颗小行星都不同，但它们大多数在未来几十年的运行轨迹都可以被预测。
And the paths of some asteroids can be predicted with incredible precision.
有一些小行星的轨迹，可以被无比精确地预测。
For example, scientists at the Jet Propulsion Laboratory
举个例子来讲，喷气推进实验室的科学家们，
predicted where the asteroid Toutatis was going to be four years in advance to within 30 kilometers.
提前四年预测了图塔迪斯小行星的位置，误差小于30公里。
In those four years, Toutatis traveled 8.5 billion kilometers. That's a fractional precision of 0.000000004.
在这四年里，图塔迪斯运行了85亿公里。小数精度为0.000000004。
Now, the reason I have this beautiful asteroid fragment is because, like all neighbors, asteroids sometimes drop by unexpectedly.
我之所以有手中这块美丽的小行星碎片，是因为，像所有的人类邻居一样，小行星有时候也会意外造访。
Three years ago today, a small asteroid exploded over the city of Chelyabinsk, Russia.
三年前的今天，一颗小型的小行星在俄罗斯的车里雅宾斯克市上方爆炸。
That object was about 19 meters across, or about as big as a convenience store.
当时，这块物体的截面长度大约为19米，和一个便利店的大小差不多。
Objects of this size hit the Earth every 50 years or so.
大约每五十年，就会有这样体积的物体撞击地球。

66 million years ago, a much larger object hit the Earth, causing a massive extinction.
六千六百万年前，一个还要大很多的物体撞击了地球，导致了大规模的生物灭绝。
75 percent of plant and animal species were lost, including, sadly, the dinosaurs.
百分之75的动植物物种都彻底消失，可悲的是，其中包括恐龙。
That object was about 10 kilometers across, and 10 kilometers is roughly the cruising altitude of a 747 jet.
当时的物体截面长度长达10公里。10公里差不多是一架波音747的飞行高度。
So the next time you're in an airplane, snag a window seat,
你下次坐飞机的时候，选一个临窗的座位，
look out and imagine a rock so enormous that resting on the ground, it just grazes your wingtip.
然后想象一下一颗巨石拔地而立，和你的机翼擦身而过。
It's so wide that it takes your plane one full minute to fly past it.
你的飞机需要飞整整一分钟才能越过它的宽度。
That's the size of the asteroid that hit the Earth.
这就是撞击地球的那颗小行星的尺寸。
It has only been within my lifetime that asteroids have been considered a credible threat to our planet.
在我们这个世代，小行星才被认为是我们星球的一个威胁。
And since then, there's been a focused effort underway to discover and catalog these objects.
那以后，我们才开始致力于对这些物体进行搜寻和纪录。
I am lucky enough to be part of this effort. I'm part of a team of scientists that use NASA's NEOWISE telescope.
我非常幸运能够参与这一个工作。我是使用NASA NEOWISE望远镜的科学家团队一员。
Now, NEOWISE was not designed to find asteroids.
要知道，NEOWISE并不是为搜寻小行星设计的。
It was designed to orbit the earth and look far beyond our solar system
它是为了能够绕行地球以遥望太阳系之外，
to seek out the coldest stars and the most luminous galaxies.
为了寻找最寒冷的星球和最明亮的星系而设计的。
And it did that very well for its designed lifetime of seven months.
在七个月的既定寿命中，它很出色地完成了任务。
But today, six years later, it's still going. We've repurposed it to discover and study asteroids.
但六年后的今天，它还在运转。我们将它的用途变成了搜寻和研究小行星。
And although it's a wonderful little space robot, these days it's kind of like a used car.
虽然它是个非常出色的太空小机器人，但现在它有些像二手车。
The cryogen that used to refrigerate its sensors is long gone, so we joke that its air-conditioning is broken.
用于传感器的制冷剂很早以前就消耗殆尽了，我们开玩笑说，空调坏了。
It's got 920 million miles on the odometer, but it still runs great and reliably takes a photograph of the sky every 11 seconds.
它的里程表上，已经有了9.2亿英里，但它依然运行良好。它每11秒就会拍一张天空的照片。
It's taken 23 photos since I began speaking to you.
从我开始演讲到现在，它已经拍了23张照片了。
One of the reasons NEOWISE is so valuable is that it sees the sky in the thermal infrared.
NEOWISE如此宝贵的原因之一是，它是通过热红外线观测天空的。
That means that instead of seeing the sunlight that asteroids reflect, NEOWISE sees the heat that they emit.
这意味着，NEOWISE看到的不是小行星折射的阳光，而是它们放散发的热量。
This is a vital capability since some asteroids are as dark as coal and can be difficult or impossible to spot with other telescopes.
这种能力至关重要，因为有些小行星暗如黑炭，几乎不可能被其他的望远镜观测到。
But all asteroids, light or dark, shine brightly for NEOWISE.
但所有的小行星，无论明暗，在NEOWISE的眼中，都一样熠熠闪耀。
Astronomers are using every technique at their disposal to discover and study asteroids.
天文学家们正在利用他们所有的技术来发现和研究小行星。
In 2010, a historic milestone was reached.
2010 年，一项历史性的里程碑得以树立。
The community, together, discovered over 90 percent of asteroids bigger than one kilometer across
通过研究者的共同努力，我们已经发现了超过90%截面长度大于一公里的小行星，
objects capable of massive destruction to Earth. But the job's not done yet.
这些物体足以给地球带来巨大的破坏。但我们的工作还没有结束。
An object 140 meters or bigger could decimate a medium-sized country.
一个横截长度大于140米的物体，就足以摧毁一个中型国家。
So far, we've only found 25 percent of those.
至今，我们只发现了25%这种大小的。
We must keep searching the sky for near-Earth asteroids.
我们必须不停地探索天空中的近地小行星。
We are the only species able to understand calculus or build telescopes.
我们是唯一能够理解微积分或者制造望远镜的物种。
We know how to find these objects. This is our responsibility.
我们知道如何找到这些物体。这是我们的责任。
If we found a hazardous asteroid with significant early warning, we could nudge it out of the way.
如果我们能够在危险的小行星出现早期就发现它们，我们就可以把它从原来的轨迹上推开。
Unlike earthquakes, hurricanes or volcanic eruptions, an asteroid impact can be precisely predicted and prevented.
不同于地震、飓风和火山爆发，我们可以准确地预测和预防小行星的冲击。
What we need to do now is map near-Earth space. We must keep searching the sky. Thank you.
我们现在需要做的是绘制出近地的空间地图。我们必须继续不停地探索天空。谢谢各位。