So to talk about where meteorites come from, we need to talk about comets and asteroids.
那么讲到流星体从何而来，我们就需要讨论下彗星和小行星。
Roids are, for the most part anyway, they are just smaller bits of asteroids and comets.
在很大程度上，Roids只是小行星和彗星的小碎片。
Rubin suggests that asteroids' heat could have derived from collisions between asteroids.
鲁宾认为，小行星的热量可能来自小行星之间的碰撞。
Earth's crust contains very little of this element, but most asteroids contain a lot more.
地壳中含有的这种元素很少，但大多数小行星上的要多得多。
I'm not going to go into any depth on comets and asteroids now, but we'll come back later and do that.
我现在不打算深入讨论彗星和小行星了，但是我们稍后会再回到这个点上，讨论这方面的内容。
The solar system also has two analogous classes of objects, smaller than planets—namely, asteroids and comets.
太阳系也有两类类似的物体，比行星还小——即小行星和彗星。
These asteroids are like the terrestrial planets, in that they're composed mostly of rocky material and metals.
这些小行星像类地行星一样，主要由岩石物质和金属构成。
The Sun is the hub of a huge rotating system consisting of nine planets, their satellites, and numerous small bodies, including asteroids, comets, and meteoroids.
太阳是一个巨大的旋转系统的中心，这个旋转系统由九大行星、它们的卫星和无数的小天体组成，包括小行星、彗星和流星体。
Skeptics have argued that a single impact would raise an asteroid's overall temperature very little and that asteroids would cool too quickly between impacts to accumulate much heat.
怀疑派认为，一次撞击只会使小行星的整体温度上升很小，而且小行星在两次撞击之间会迅速冷却，从而无法积聚大量热量。
A recent discovery that asteroids are highly porous makes Rubin's hypothesis more plausible.
最近的一项发现表明小行星非常多孔，这使得鲁宾的假设更加可信。
Watery Asteroids Also a Source?
小行星上的水也是来源之一？
大角度：小行星！
Water has already been found on asteroids.
水已被发现在小行星。
Explore an asteroids and comets interactive.
探索一颗小行星和彗星们的相互作用。
Asteroids May Have Brought Precious Metals to earth.
小行星可能把贵金属带到地球。
Dr Bottke has been tracking the orbits of asteroids.
伯克(Bottke)博士一直在追踪小行星的运行轨迹。
If there were no asteroids would there be no extinctions?
如果没有小行星，就不会有灭绝了吗？
Experiments could also be performed for mining asteroids.
实验也可以进行挖掘小行星。
Astronomers know these condense into planets and asteroids.
而天文学家知道这些云状物最终将凝结成大小行星。
They could similarly sample near-Earth objects like asteroids.
他们同样可以在像小行星这样的近地物体的提取样本。
For more information about asteroids and near-Earth objects, visit.
更多的关于小行星和近体天体的信息请参阅。
Asteroids may want to think twice before they swing too close to Earth.
小行星在过于飞近地球之前可能会再三考虑一下。
It's most likely the result of a recent collision between two asteroids.
这很可能是两个小行星之间相撞产生的结果。
This iteration of Orion is intended for trips to Mars or far-off asteroids.
猎户座的迭代是为了打算远行到火星或遥远的小行星。
Scale models of asteroids fill the windowsill of his office at JPL in Pasadena.
在帕萨迪纳喷气推进实验室，他办公室的窗台上摆满了小行星按比例制作的模型。
Just as most orbiting planets spin on their axes, so asteroids also rotate.
正如其它沿轨道运行的行星自转一样，这些小行星也有自转。
Apollo asteroids pose a threat to our planet as they routinely cross Earth's orbit.
阿波罗型小行星因定期地穿越地球轨道而构对地球的威胁。
This goes on until the particles get to the size of boulders or small asteroids.
这现象一直持续，直到微粒达到巨石或者是微型小行星的大小。
Asteroids classify comets based on the durations of their orbits around the sun.
天文学上把彗星按照它们的轨道周期分类。
Asteroids classify comets based on the durations of their orbits around the sun.
天文学上把彗星按照它们的轨道周期分类。
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