The Formation Of Gas Planets托福听力原文翻译及问题答案

The Formation Of Gas Planets托福听力原文翻译及问题答案

一、The Formation Of Gas Planets托福听力原文：

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托福听力中文翻译：

旁白：在天文学课上听一节课的一部分。

男教授：上周我们讨论了地球和其他岩石行星的形成——太阳系内部的行星。呃，那么，气态巨行星呢？木星、土星、天王星和海王星。

有两种理论。但首先，让我们回顾一下。我们相信，我们的太阳系最初是一团巨大的旋转的尘埃和气体云，它变平并最终自行坍塌。它的中心物质凝结成一团炽热的气体和尘埃，最终成为我们的太阳。剩下的云怎么了？

当它还是一颗年轻的恒星时，围绕太阳的圆盘？女学生：岩石行星诞生了。嗯，尘埃圆盘内的小颗粒岩石和金属相互碰撞并粘在一起。这一过程在数百万年的时间里像滚雪球一样发展。。。直到这些块体成长为迷你行星-原行星。

男教授：是的。这个过程叫做吸积。我们称之为吸积盘。现在把它看作两部分，一个内部吸积盘和一个外部吸积盘。在内部，一旦一个物体变得足够大，该物体的引力场就会变得更强，从而加速吸积过程。你知道，较大的物体会吸引较小的物体并将其吞噬。最终，你会在自己的轨道上看到一颗全尺寸的行星。

可以这就是内部岩石行星可能是如何通过吸积作用形成的。

但是那些位于太阳系外部吸积盘中的气体行星呢？

第一种理论认为，吸积过程与形成岩石行星的过程相似，但有一些关键的区别。

记住，气态巨行星离太阳更远，那里的温度要低得多。因此，在外部吸积盘中，水和氨等化合物以冻结的形式存在。离太阳越近，它们越容易被太阳辐射蒸发。这意味着，除了岩石和金属颗粒外，还会有其他固体，如冷冻水和冷冻氨。女生：。。。所以有更多的固体物质可以聚集成原行星，对吗？男教授：没错！因此，可以想象，气态巨行星的固体核心是通过吸积作用形成的。一旦它们的质量达到某个点，大约5到10个地球，会发生什么？女生：五到十个地球？有这么大的质量，我想重力会更快地吸引越来越多的物质，对吗？男教授：材料，意思是气体。它会迅速从吸积盘中吸入越来越多的气体，因此最终形成一个由岩石、金属和冰组成的固体核心，周围环绕着大量的气体。这就是核心吸积理论。另一种理论叫做圆盘不稳定性理论。圆盘不稳定性理论认为，气体在没有固体核心的情况下开始了行星的形成过程。你看，大部分外部吸积盘都是气体。我们相信固体粒子可能只占外部吸积盘的1%。

所以这个理论表明，大型行星，气态巨行星，呃，它们是由吸积盘中的大量气体和尘埃形成的。吸积盘的外部区域可能是不稳定的，引力不稳定的，这就是导致这些团块形成的原因，在某些情况下，会生长成原行星。

随着时间的推移，气体中的尘埃颗粒聚结在一起，结合在一起，最终朝中心下落，形成一个核心。一旦发生这种情况，气体团块增长相对较快，因为其重力吸引了越来越多的气体和尘埃颗粒。理论上，整个过程可以在十万年内完成。

女学生：真是太快了！那么，哪个理论是正确的？

男教授：这就是辩论。我的大多数同事都赞成核吸积。我个人认为吸积理论适用于岩石行星的形成，但不一定适用于气体行星。一个主要的问题是像木星和土星这样的气态巨行星需要很长时间才能通过核心吸积形成。堆芯吸积需要数百万年的时间。但对其他恒星系统的观测表明，圆盘中的气体消失得更快。没有被行星吸引的物质最终会被附近恒星的太阳风和辐射所消散和蒸发。所以基本上，幼小的木星在长大之前就会耗尽气体。但圆盘不稳定性理论。。。嗯，时机是对的。这个过程足够快，可以在气体耗尽之前完成。

三、The Formation Of Gas Planets托福听力问题：

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托福听力答案：

A1:正确答案：B

A2:正确答案：C

A3:正确答案：A

A4:正确答案：B

A5:正确答案：AD

A6:正确答案：D

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