評(píng)論
打印
Narrator:Listen to part of a lecture in an astronomy class.
獨(dú)白:聽下面一段天文學(xué)課上的演講。
Professor:OK, I wanna go over the different types of meteoroids, and what we've learned from them about the formation of earth, and solar system.
教授:好的，我要講一下各種不同的流星體，以及我們從這些流星體上獲取的關(guān)于地球構(gòu)造和太陽系的信息。
Uh… the thing is what's especially interesting about meteoroids is that they come from interplanetary space, but they consist of the same chemical elements that are in matter originated on earth, just in different proportions.
額，流星體特別有趣的一點(diǎn)是，這些流星體來自行星際空間，但是他們包含著同樣的化學(xué)元素，這些物質(zhì)來源于地球，只是成分所占比例不同而已。
But that makes it easier to identify something as a meteoroid, as it opposed to…to just a terrestrial rock.
但正因?yàn)槿绱巳藗兛梢愿菀妆嬲J(rèn)出流星體，而不會(huì)將其當(dāng)做一種地球上的巖石。
So to talk about where meteoroids come from, we need to talk about comets and asteroids, which basically...they're basically made up of debris left over from the origin of the solar system 4.6 billion years ago.
那么講到流星體從何而來，我們就需要討論下彗星和小行星，基本上說，這些流星體是由 46 億年前太陽系誕生以來留下的廢墟組成的。
Now I'm going a bit out of a boarder here…umm…I'm not going to go into any depth on the comets and asteroids now, but we'll come back later and do that.
現(xiàn)在，我要講一下題外話，嗯，我現(xiàn)在不會(huì)詳細(xì)深入講彗星或小行星，我們以后再深入講解。
From now, I'll just cover some basic info about them.
從現(xiàn)在開始，我會(huì)只講一些基本信息。
OK, comets and asteroids.
好的，彗星和小行星。
It might help if you think of...remember we talked about the two classes of planets in our solar system?
這可能會(huì)對(duì)你們有所幫助，如果你想到……記得我們說過太陽系中的兩類行星嗎？
And how they differ in composition?
還有他們?cè)诔煞稚嫌惺裁床煌模?/div>
The terrestrial planets--like Mars and Earth--composed largely of rocks and metals, and the large gas giants, like Jupiter.
類地行星，像火星或地球，大部分是由巖石和金屬構(gòu)成的。另一種就像木星這種大行星，其星體上布滿氣體。
Well, the solar system also has two analogous classes of objects, smaller than planets--namely, asteroids and comets.
嗯，太陽系中還有兩種相類似的星體分類，比行星要小，那就是小行星和彗星。
Relatively near the sun and inner solar system, between Jupiter and Mars to be precise, we've got the asteroid belt, which contains about 90 percents of all asteroids orbiting the sun.
相對(duì)而言，這些星體更接近太陽和太陽系內(nèi)部，確切地說，處于木星和火星之間。我們知道小行星帶的存在，這里面有 90%的小行星是繞著太陽而旋轉(zhuǎn)的。
These asteroids are…uh…like the terrestrial planets, and they're composed mostly of rocky materials and metals.
這些小行星，額，就像是類地行星。他們主要是由巖石材料和金屬構(gòu)成的。
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 methane and carbon dioxide.
在遠(yuǎn)離太陽的地方，在太陽系外延，木星軌道之外，那里的氣溫很低，足以使某些水分凝結(jié)成冰，而且，釋放出像甲烷和二氧化碳這樣的氣體。
Loose collections of these ices and small rocky particles form into comets.
這些冰塊和小型的巖石微粒會(huì)集合起來，形成彗星。
So comets are similar in composition to the gas giants.
所以彗星的成分和氣體巨星的成分是相類似的。
Both comets and asteroids are...typically are smaller than planets.
彗星和小行星都要比行星小很多。
And even smaller type of interplanetary debris is the meteoroid.
而甚至是更為小型的行星間的碎片也是行星體。
And it's from meteoroids that we get meteors and meteorites.
而從這些行星體中會(huì)有流星和隕石。
"Roids" are, for the most part anyway, they are just smaller bits of asteroids and comets.
“Roids”通常上講，只是小行星和彗星的小型碎片。
When these bits enter earth's atmosphere, well, that makes them so special that they get a special name.
當(dāng)這些碎片進(jìn)入地球大氣層之后，它們便會(huì)變得很特別，會(huì)有一個(gè)特別的名字，
They're called meteors.
它們被稱為流星。
Most of them are very small, and they burn up soon after entering earth's atmosphere.
大部分流星都體積很小，在進(jìn)入大氣層之后會(huì)很快燃燒起來。
The larger ones that make it through the atmosphere and hit the ground are called meteorites.
那些體積較大，進(jìn)入大氣層之后直擊地面的流星便叫做隕石。
So meteorites are the ones that actually make it through.
因此隕石其實(shí)就是那些穿透大氣層到達(dá)地球表面的行星體。
Now we've been finding meteorites on earth for thousands of years, 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.
如今我們發(fā)現(xiàn)隕石的歷史已經(jīng)有幾千年了，我們已經(jīng)對(duì)其進(jìn)行了足夠的分析，解了很多關(guān)于隕石的成分，知道大部分是來自小行星，盡管有些隕石是來自彗星。
So essentially they are rocks, and like rocks, they're mixtures of minerals.
所以，基本上講，這些隕石就是巖石。它們是各種礦物的混合物。
They are generally classified into three broad categories--stones, stony irons and irons.
基本上被分為三大類:石頭，隕鐵石和鐵塊。
Stone meteoroids, which we refer to simply as, uh, stones, are almost entirely rock material.
某些行星體，我們簡(jiǎn)單稱為，額，石頭，基本上全部是巖石材料。
They actually account for almost all of the meteorite material that falls to earth.
事實(shí)上它們幾乎占到所有落到地球表面隕石材料的全部。
But even so, it's rare to ever find one.
但即便如此，找到顆隕石都難。
I mean, it's easier to find an iron meteorite or stony iron.
我是說，找到一塊鐵隕星或隕鐵石會(huì)更容易點(diǎn)。
Anyone guess why? Look at their names.
有人知道為什么嗎？看看這些名字，
What do you think iron meteorites consist of?
你們覺得隕鐵石包括什么呢？
Student:Mostly iron?
學(xué)生:大部分是鐵吧？
Professor:Yeah… iron and some nickel, both of which are metals.
教授:是的，鐵和鎳，兩者都是金屬成分，
And, if you're trying to find metal?
而如果你正試圖找某些金屬材料的話？
Student:Oh! Metal detectors!
學(xué)生:哦！金屬探測(cè)器！
Professor:Right, thank you.
教授:好的，謝謝。
At least that's part of it.
至少這是其中的一部分。
Stone meteoroids, 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-once that originated on earth.
如果暴露在某種天氣中幾年，嗯，由于他們都是由石頭構(gòu)成的，所以基本上這些石隕石跟那些普通的地球上的石頭并無兩樣。
So it's hard to spot them by eye.
而要靠肉眼來察覺這些星體是比較難的。
But we can use metal detectors to help us find the others, and they're easier to spot by eye.
但是我們能用金屬測(cè)探器幫助我們找到其他流星體，這些能更容易通過肉眼看到。
So most of the meteorites in collections, uh, in museums, they'll be...they're iron meteorites, or the stony iron kind, even though they only make up about 5percents of the meteorite material on the ground.
因此大部分聚合起來的隕石，額，在博物館中的，它們將會(huì)，它們是鐵隕星，或是隕鐵石，即便這些星體只占到地面上的隕星材料的 5%。
