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Narrator: Listen to part of a lecture in an Astronomy class.

教授：OK，我想复习一下不同类型的陨石，我们从它们身上已经了解了地球形成的内容，以及太阳系。

Male professor: OK, I want to go over the different types of meteorites and what we've learned about them from the formation of earth and the solar system.

呃……关于陨石特别有趣的事情是，他们来自星际空间，但它们由来源于地球上相同的化学元素组成，只是比例不同。

Uh, the thing is, what's especially interesting about meteorites is that they come from interplanetary space, but they consist of the same chemical elements that are in matter originating on earth, just in different proportions.

但是，这使得我们更容易将东西识别为陨石，而不是……只是地面的岩石。

But that makes it easier to identify something as a meteorite as opposed to just a terrestrial rock.

所以要讨论陨石从哪里来，我们需要谈谈彗星和小行星，它们基本上……它们基本上是由在46亿年前在太阳系起源遗留下来的碎片组成的。

So to talk about where meteorites come from, we need to talk about comets and asteroids, which basically, they are basically made up of debris left over from the origin of the solar system 4.6 billion years ago.

现在我要颠倒下顺序……嗯……

Now I'm going a bit out of order here, um.

我不打算深入讨论彗星和小行星，但我们将在之后讨论。

I'm not going to go into any depth on comets and asteroids now, but we will come back later and do that.

现在，我就说说关于他们的一些基本信息。

For now, I'll just cover some basic info about them.

OK，彗星和小行星，它可能会帮助，如果你想……还记得我们谈到的我们太阳系中两类行星吗？

OK, comets and asteroids, it might help if you think of, remember we talked about the two classes of planets in our solar system?

类地行星，就像火星和地球，主要是由岩石和金属组成？

The terrestrial planets like Mars and Earth, composed largely of rocks and metals?

那么，太阳系也有两个相似类型的对象，比行星小，即小行星和彗星，比较靠近太阳，在太阳系内，精确地说是在木星和火星之间。

Well, the solar system also has two analogous classes of objects smaller than planets, namely asteroids and comets, relatively near the Sun, in the inner solar system between Jupiter and Mars to be precise.

我们已经有了小行星带，其中包含绕太阳的所有小行星的90%。

We've got the asteroid belt, which contains about 90 percent of all asteroids orbiting the Sun.

这些小行星是……呃……像陆地行星，因为他们大多是由岩石材料和金属组成。

These asteroids are, uh, like the terrestrial planets in that they are composed mostly of rocky material and metals.

远离太阳，在太阳系外围，超越木星的轨道，温度足够低，水形成冰……甲烷和二氧化碳之类的气体也形成冰。

Far from the Sun, in the outer solar system, beyond Jupiter's orbit, temperatures are low enough to permit ices to form out of water and, and out of gases like, uh, methane and carbon dioxide.

这些冰和小岩石颗粒组建成彗星。

Loose collections of these ices and small rocky particles form into comets.

所以彗星和气体巨星在组成成分上相似。

So comets are similar in composition to the gas giants.

无论彗星和小行星……通常比行星小得多。

Both comets and asteroids are, typically are smaller than planets.

一个更小的类型星际碎片是流星体。

And even smaller type of interplanetary debris is the meteoroid.

我们从流星体得到流星和陨石。

And it's from the meteoroids that we get meteors and meteorites.

Roid，在大多数情况下，他们只是小行星和彗星小块片。

Roids are, for the most part anyway, they're just smaller bits of asteroids and comets.

当这些小块片进入地球大气层，嗯，这让它们如此特殊，它们得到一个特别的名字，他们被称为流星。

When these bits enter earth's atmosphere, well, that makes them so special that they get a special name: they're called meteors.

他们大多是非常小的，而且他们在进入地球大气层后燃烧起来很快。

Most of them are very small and they burn up soon after entering earth's atmosphere.

较大的成功穿越大气层并砸到地面上的碎片，被称为陨石。

The larger ones that make it through the atmosphere and hit the ground are called meteorites.

因此，陨石是那些真正成功穿过大气层的那些。

So meteorites are the ones that actually make it through.

现在，几千年来，我们已经在地球上发现了陨石。

Now, we've been finding meteorites on earth for thousands of years.

我们已经分析了他们，足够的了解了很多关于它们的组成，大部分是来自小行星，虽然一些可能来自彗星。

And we've analyzed enough of them to learn a lot about their composition, most come from asteroids, though a few may have come from comets.

所以基本上他们是岩石或像石头一样。

And like rocks, they are mixtures of minerals.

他们一般分为三大类：石头，陨铁石和铁。

They are generally classified into three broad categories: stones, stony irons and irons.

石陨石，我们简单的称之为，呃，石头，几乎完全是岩石材料。

Stone meteorites, which we refer to simply as, uh, stones, are almost entirely rock material.

他们实际上几乎占据了所有的落到地球上的陨石材料。

They actually account for almost all of the meteorite material that falls to earth.

我的意思是，找到一个铁陨石或石铁更容易。

I mean, it's easier to find an iron meteorite or stony iron.

What do you think iron meteorites consist of?

教授：是的，铁和一些镍，两个都是金属。

Professor: Yeah! Iron and some nickel, both of which are metals.

那么，当你想要找到金属的时候？

石陨石，如果他们闲置着，被暴露于风雨中几十年之后，它们是由岩石组成的，所以他们最终看上去和普通地面的岩石几乎没有区别，那些起源于地球的岩石。

Stone meteorites, if they lie around exposed to the weather for a few years, well, they're made of rock, so they end up looking almost indistinguishable from common terrestrial rocks, ones that originated on earth.

但我们可以用金属探测器来帮助我们找到其他的。

But we can use metal detectors to help us find the others.

所以大部分的陨石收藏中，呃，博物馆，都是陨铁，或陨铁石，即使他们只是大约构成了地面上的陨石材料的5％。

So most of the meteorites in collections, uh, in museums, they'll be, they are iron meteorites, or the stony iron kind, even though they only make up about 5 percent of the meteorite material on the ground.

What comparison does the professor make to help describe the composition of asteroids and comets?

What does the professor say about the origin of meteors and meteorites?

According to the professor, what feature of a meteoroid generally determines whether the meteoroid becomes a meteorite?

What are two points the professor makes about stone meteorites?

Listen again to part of the Lecture. Then answer the question Why does the professor say this: