The Formation Of Gas Planets托福聽力原文翻譯及問題答案

The Formation Of Gas Planets托福聽力原文翻譯及問題答案

一、The Formation Of Gas Planets托福聽力原文：

NARRATOR:Listen to part of a lecture in an astronomy class.

MALE PROFESSOR:Last week we discussed the formation of Earth and the other rocky planets—the planets in the inner solar system.Uh,s-so,what about the gas giants?Jupiter,Saturn,Uranus,and Neptune.

Well,there's two theories.But first,let's recap.We believe our solar system began as a huge spinning cloud of dust and gas,which flattened and eventually collapsed in on itself.The matter it's centered condensed into a ball of hot gas and dust,eventually becoming our sun.And what happened to the remaining cloud?

To the disk encircling the sun when it was a young star?FEMALE STUDENT:The rocky planets were born.Um,dust—little grains of rock and metal within the disk collided with each other and stuck together.And this process sorta snowballed over millions of years...until the chunks grew into mini-planets—protoplanets.

MALE PROFESSOR:Yeah.This process is called accretion.And we call the disk an accretion disk.Now...think of it as two parts—an inner accretion disk and an outer accretion disk.In the inner part,once an object gets large enough,that object's gravitational field gets stronger,which speeds up the accretion process.You know,larger objects attract smaller ones and sort of gobble them up.And eventually,you get a full-sized planet in its own orbit.

Okay.That's how the inner rocky planets probably formed—by accretion.

But what about those gas planets in the outer solar system,in the outer accretion disk?

Well,the first theory says the accretion process was similar to the one that formed the rocky planets,with some key differences.

Remember,the gas giants are farther from the sun,where temperatures are much colder.So,in the outer accretion disk,compounds like water and ammonia exist in frozen form.Closer to the sun,they're more likely to be vaporized by solar radiation.What this means is that in addition to rocky and metallic particles there would be other solids like frozen water and frozen ammonia.FEMALE STUDENT:...so more solid substances are available to clump into protoplanets,right?MALE PROFESSOR:Precisely!So the solid cores of the gas giants could conceivably have formed by accretion.And once their mass reaches a certain point,around about 5 to 10 Earths,what would happen?FEMALE STUDENT:Five to ten Earths?With a mass that big,I guess gravity would start to pull in more and more material faster,right?MALE PROFESSOR:Material,meaning gas.It would rapidly pull in more and more gas from the accretion disk,so you end up with a solid core of rock,metal and ice surrounded by massive amounts of gas.That's the core accretion theory.Now,the other theory is called the disk instability theory.The disk-instability theory holds that gas begins the planet-making process,without a solid core.You see,most of the outer accretion disk would have been gas.We believe solid particles probably made up just one percent of the outer accretion disk.

So this theory suggests that large planets,the gas giants,uh,they develop from large clumps of mostly gas and some dust in an accretion disk.Outer regions of an accretion disk can be unstable,gravitationally unstable,which is what causes these clumps to form,and in some cases,grow in to proto-planets.

Over time,dust particles within a gas clump coalesce,bond together,and eventually fall toward the center,creating a core.Once this happens,the gas clump grows relatively quickly as its gravity pulls in more and more gas and dust particles.And this whole process can theoretically happen within one hundred thousand years.

FEMALE STUDENT:That's amazingly fast!So,which theory's correct?

MALE PROFESSOR:That's the debate.Most of my colleagues favor core accretion.Personally,I think the accretion theory works for the formation of rocky planets,but not necessarily for gas planets.A major problem is that gas giants like Jupiter and Saturn would take too long to form through core accretion.Core accretion would take several million years.But observations of other star systems indicate that a disk's gas disappears more quickly than that.Whatever's not drawn into planets ends up dissipated and evaporated by solar wind and radiation,from nearby stars.So basically,a baby Jupiter would run out of gas before it grew up.But the disk-instability theory...well,the timing's right.That process is fast enough to finish before the gas runs out.

二、The Formation Of Gas Planets托福聽力中文翻譯：

旁白：在天文學(xué)課上聽一節(jié)課的一部分。

男教授：上周我們討論了地球和其他巖石行星的形成——太陽系內(nèi)部的行星。呃，那么，氣態(tài)巨行星呢？木星、土星、天王星和海王星。

有兩種理論。但首先，讓我們回顧一下。我們相信，我們的太陽系最初是一團(tuán)巨大的旋轉(zhuǎn)的塵埃和氣體云，它變平并最終自行坍塌。它的中心物質(zhì)凝結(jié)成一團(tuán)熾熱的氣體和塵埃，最終成為我們的太陽。剩下的云怎么了？

當(dāng)它還是一顆年輕的恒星時(shí)，圍繞太陽的圓盤？女學(xué)生：巖石行星誕生了。嗯，塵埃圓盤內(nèi)的小顆粒巖石和金屬相互碰撞并粘在一起。這一過程在數(shù)百萬年的時(shí)間里像滾雪球一樣發(fā)展。。。直到這些塊體成長(zhǎng)為迷你行星-原行星。

男教授：是的。這個(gè)過程叫做吸積。我們稱之為吸積盤。現(xiàn)在把它看作兩部分，一個(gè)內(nèi)部吸積盤和一個(gè)外部吸積盤。在內(nèi)部，一旦一個(gè)物體變得足夠大，該物體的引力場(chǎng)就會(huì)變得更強(qiáng)，從而加速吸積過程。你知道，較大的物體會(huì)吸引較小的物體并將其吞噬。最終，你會(huì)在自己的軌道上看到一顆全尺寸的行星。

可以這就是內(nèi)部巖石行星可能是如何通過吸積作用形成的。

但是那些位于太陽系外部吸積盤中的氣體行星呢？

第一種理論認(rèn)為，吸積過程與形成巖石行星的過程相似，但有一些關(guān)鍵的區(qū)別。

記住，氣態(tài)巨行星離太陽更遠(yuǎn)，那里的溫度要低得多。因此，在外部吸積盤中，水和氨等化合物以凍結(jié)的形式存在。離太陽越近，它們?cè)饺菀妆惶栞椛湔舭l(fā)。這意味著，除了巖石和金屬顆粒外，還會(huì)有其他固體，如冷凍水和冷凍氨。女生：。。。所以有更多的固體物質(zhì)可以聚集成原行星，對(duì)嗎？男教授：沒錯(cuò)！因此，可以想象，氣態(tài)巨行星的固體核心是通過吸積作用形成的。一旦它們的質(zhì)量達(dá)到某個(gè)點(diǎn)，大約5到10個(gè)地球，會(huì)發(fā)生什么？女生：五到十個(gè)地球？有這么大的質(zhì)量，我想重力會(huì)更快地吸引越來越多的物質(zhì)，對(duì)嗎？男教授：材料，意思是氣體。它會(huì)迅速?gòu)奈e盤中吸入越來越多的氣體，因此最終形成一個(gè)由巖石、金屬和冰組成的固體核心，周圍環(huán)繞著大量的氣體。這就是核心吸積理論。另一種理論叫做圓盤不穩(wěn)定性理論。圓盤不穩(wěn)定性理論認(rèn)為，氣體在沒有固體核心的情況下開始了行星的形成過程。你看，大部分外部吸積盤都是氣體。我們相信固體粒子可能只占外部吸積盤的1%。

所以這個(gè)理論表明，大型行星，氣態(tài)巨行星，呃，它們是由吸積盤中的大量氣體和塵埃形成的。吸積盤的外部區(qū)域可能是不穩(wěn)定的，引力不穩(wěn)定的，這就是導(dǎo)致這些團(tuán)塊形成的原因，在某些情況下，會(huì)生長(zhǎng)成原行星。

隨著時(shí)間的推移，氣體中的塵埃顆粒聚結(jié)在一起，結(jié)合在一起，最終朝中心下落，形成一個(gè)核心。一旦發(fā)生這種情況，氣體團(tuán)塊增長(zhǎng)相對(duì)較快，因?yàn)槠渲亓ξ嗽絹碓蕉嗟臍怏w和塵埃顆粒。理論上，整個(gè)過程可以在十萬年內(nèi)完成。

女學(xué)生：真是太快了！那么，哪個(gè)理論是正確的？

男教授：這就是辯論。我的大多數(shù)同事都贊成核吸積。我個(gè)人認(rèn)為吸積理論適用于巖石行星的形成，但不一定適用于氣體行星。一個(gè)主要的問題是像木星和土星這樣的氣態(tài)巨行星需要很長(zhǎng)時(shí)間才能通過核心吸積形成。堆芯吸積需要數(shù)百萬年的時(shí)間。但對(duì)其他恒星系統(tǒng)的觀測(cè)表明，圓盤中的氣體消失得更快。沒有被行星吸引的物質(zhì)最終會(huì)被附近恒星的太陽風(fēng)和輻射所消散和蒸發(fā)。所以基本上，幼小的木星在長(zhǎng)大之前就會(huì)耗盡氣體。但圓盤不穩(wěn)定性理論。。。嗯，時(shí)機(jī)是對(duì)的。這個(gè)過程足夠快，可以在氣體耗盡之前完成。

三、The Formation Of Gas Planets托福聽力問題：

Q1:1.What is the main purpose of the lecture?

A.To describe two new theories about the formation of rocky planets.

B.To discuss competing theories about the formation of gas planets.

C.To compare the composition of Jupiter,Saturn,Uranus,and Neptune.

D.To explain why young stars are often surrounded by disks of gas and dust.

Q2:2.Why does the professor review the formation of rocky planets?

A.To contrast it with the formation of the Sun.

B.To correct a common misunderstanding about accretion.

C.To use the information as the basis for another topic of discussion.

D.To introduce recent discoveries about rocky planets in other solar systems.

Q3:3.What point does the professor emphasize when he mentions water and ammonia?

A.Solid forms of water and ammonia may have contributed to the formation of the gas giants.

B.Water and ammonia were not common substances in the outer accretion disk.

C.Water and ammonia are pulled in by the gravity of protoplanets more readily than other substances are.

D.Most substances found in the core of rocky planets are also found in the core of gas planets.

Q4:4.According to the professor,what could have occurred when a protoplanet in the outer accretion disk reached a mass of five to ten Earths?

A.It started to shed grains of rock and metal into the solar system.

B.Its gravity began to pull in huge amounts of the surrounding gas.

C.Its gravity caused clumps to form in the surrounding gas.

D.It collided with smaller protoplanets.

Q5:5.According to the professor,what are two claims of the disk-instability theory?[Click on 2 answers.]

A.Gas planet formation did not begin with a solid core.

B.Gas planets cannot form in extremely cold temperatures.

C.Gas planet formation can occur anywhere in the accretion disk.

D.Gas planets form over a relatively short time.

Q6:6.Which is the professor's opinion about the disk-instability theory?

A.It differs from the core-accretion theory in relatively insignificant ways.

B.It does not take into account the amount of time needed for gas planets to form.

C.It is more applicable to star formation than the core-accretion theory is.

D.Solid particles are believed to own a small proportion of the outer accretion disk.

四、The Formation Of Gas Planets托福聽力答案：

A1:正確答案：B

A2:正確答案：C

A3:正確答案：A

A4:正確答案：B

A5:正確答案：AD

A6:正確答案：D

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