『新东方在线托福阅读』为托福考生准备了ETS托福TPO/Official 42 Passage 3阅读练习：Why does the author provide the information that “It is much easier for an icy body to differentiate than for a rocky one”?真题题目及答案解析，TPO/Official 42 Passage 3阅读原文范文音频翻译

托福TPO/Official 42 Passage 3阅读原文Why does the author provide the information that “It is much easier for an icy body to differentiate than for a rocky one”?题目答案及解析-新东方托福官方网校手机版

从1996年到1999年，伽利略太空飞船穿过了木星系统，提供了关于木星卫星的很多信息。

From 1996 to 1999, the Galileo spacecraft passed through the Jovian system, providing much information about Jupiter’s satellites.

木卫四，也就是木星四颗最大卫星的最外层，周期为17天绕木星运转，轨道半径为200万千米。

Callisto, the outermost of Jupiter’s four largest satellites, orbits the planet in seventeen days at a distance from Jupiter of two million kilometers.

正如月球一样，木卫四自转和绕木星公转的周期一样，所以它一直是同样的一面朝着木星。

Like our own Moon, Callisto rotates in the same period as it revolves, so it always keeps the same face toward Jupiter.

它的正午表面温度仅仅−140ºC，所以冰全年在它的表面都是很稳定的状态。

Its noontime surface temperature is only about −140ºC, so water ice is stable on its surface year-round.

木卫四的直径是4820千米，几乎和水星的一样。

Callisto has a diameter of 4,820 kilometers, almost the same as that of Mercury.

它的质量仅仅是水星的三分之一，这意味着它的密度也仅仅是水星的三分之一。

Its mass is only one-third as great, which means its density must be only one-third as great as well.

这就提醒我们木卫四有远少于其他行星内部的岩石金属物质，它的内部绝大多数是冰。

This tells us that Callisto has far less of the rocky metallic materials found in the inner planets and must instead be an icy body through much of its interior.

木卫四还没有完全分化，这也就意味着它的内部还没有分化成密度不同的几层。

Callisto has not fully differentiated, meaning separated into layers of different density materials.

通过在几次距离很近的运转时伽利略号太空飞船的重力探测细节，天文学家得知，木卫四缺乏一个高密度的内核。

Astronomers can tell that it lacks a dense core from the details of its gravitational pull on the Galileo spacecraft during several very close flybys.

这个事情使得科学家很震惊，他们都认为所有大的冰卫星都分层了。

This fact surprised scientists, who expected that all the big icy moons would be differentiated.

因为冰的熔点那么低，所以冰天体相比岩石天体更容易分化。

It is much easier for an icy body to differentiate than for a rocky one, since the melting temperature of ice is so low.

仅仅一点点的加热就能使冰融化，并且使这个进程开始，能够让岩石和金属沉到中心，冰沙漂浮到表面。

Only a little heating will soften the ice and get the process started, allowing the rock and metal to sink to the center and the slushy ice to float to the surface.

但是在分层过程完成之前，木卫四似乎冻得很结实。

Yet Callisto seems to have frozen solid before the process of differentiation was complete.

就像是月球的高地一样，木卫四的表面被撞击坑所覆盖。

Like our Moon’s highlands, the surface of Callisto is covered with impact craters.

这些撞击坑的存在告诉我们，冰天体能够形成并且使得撞击坑保存在它的表面上。

The survival of these craters tells us that an icy object can form and retain impact craters in its surface.

一想到冰体距离太阳那么远，不去根据我们熟知的在地球上的温度更高的冰去判断天体上冰体的行为是很重要的；在外太阳系的气温下，天体表面的冰坚如岩石，性能也和岩石相似。

In thinking of ice so far from the Sun, it is important not to judge its behavior from that of the much warmer ice we know on Earth; at the temperatures of the outer solar system, ice on the surface is nearly as hard as rock, and behaves similarly.

木卫四上的冰体不会像地球冰川的冰一样变形或者流动。

Ice on Callisto does not deform or flow like ice in glaciers on Earth.

木卫四在太阳系行星大小的天体中是独一无二的，因为它缺乏内部的力量去驱使地质演化。

Callisto is unique among the planet-sized objects of the solar system in its absence of interior forces to drive geological evolution.

当卫星刚刚形成的时候就是死的，并且在超过四十亿的时间里都保持了地质的不变。

The satellite was born dead and has remained geologically dead for more than four billion years.

木卫三是木星的另外一颗卫星，并且是太阳系里面最大的，它也是成坑状的，但是不如木卫四那样严重。

Ganymede, another of Jupiter’s satellites and the largest in our solar system, is also cratered, but less so than Callisto.

木卫三表面大约四分之一都很老了，并且严重的成坑化；剩余的最近才形成，我们可以从稀稀疏疏的撞击坑相对比较新的撞击坑看得出来。

About one-quarter of its surface seems to be as old and heavily cratered; the rest formed more recently, as we can tell by the sparse covering of impact craters as well as the relative freshness of the craters.

木卫三是分层的，就像是类地行星一样。

Ganymede is a differentiated world, like the terrestrial planets.

重力场的测量告诉我们，岩石和金属下沉形成了像是月球一样大小的内核，冰地幔和地壳漂浮在上方。

Measurements of its gravity field tell us that the rock and metal sank to form a core about the size of our Moon, with a mantle and crust of ice floating above it.

除此之外，伽利略号太空飞船发现，木卫三有磁场，这是它的内部一部分已经熔融的标志。

In addition, the Galileo spacecraft discovered that Ganymede has a magnetic field, the signature of a partially molten interior.

木卫三并不是一个死卫星，而是靠内部热供能的一个有持续不断的地质活动的天体。

Ganymede is not a dead world, but rather a place of continuing geological activity powered by an internal heat source.

它的表面的大部分可能仅仅形成有五亿年左右。

Much of its surface may be as young as half a billion years.

较年轻的地带就是地壳运动和火山运动的结果。

The younger terrain is the result of tectonic and volcanic forces.

当地壳裂开后，有些地貌就形成了，内部的水会冲刷很多的撞击坑。

Some features formed when the crust cracked, flooding many of the craters with water from the interior.

由于地壳的挤压，绵长的山脉就形成了，同时形成了长长的山脊和间隔一到两千米的平行的山谷。

Extensive mountain ranges were formed from compression of the crust, forming long ridges with parallel valleys spaced one to two kilometers apart.

在一些地方，较老的撞击坑被分裂开了。

In some places older impact craters were split and pulled apart.

甚至有迹象表明木卫三有大规模的外壳运动的标志，这些外壳运动类似于地球板块运动。

There are even indications of large-scale crustal movements that are similar to the plate tectonics of Earth.

为什么木卫三和木卫四不同呢？可能是因为体积大小和内部热量的微小差异导致了它们演化过程中的差异化。

Why is Ganymede different from Callisto? Possibly the small difference in size and internal heating between the two led to this divergence in their evolution.

但是更有可能的是，木星的引力造成了木卫三持续不断的地质运动。

But more likely the gravity of Jupiter is to blame for Ganymede’s continuing geological activity.

木卫三距离木星足够近，因此在那颗大行星上的潮汐力可能会偶尔使得木卫三内核温度升高并且引发它外壳的巨大运动。

Ganymede is close enough to Jupiter that tidal forces from the giant planet may have episodically heated its interior and triggered major convulsions on its crust.

According to paragraph 1, which of the following statements about Callisto is true?

According to paragraph 1, how do scientists know that Callisto is made up largely of ice?

Why does the author provide the information that “It is much easier for an icy body to differentiate than for a rocky one”?

All of the following questions are answered in paragraph 2 EXCEPT:

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

According to paragraph 3, how is Callisto different from all other planet-sized objects in the solar system?

The word “signature” in the passage is closest in meaning to

According to paragraph 4, each of the following provides evidence about Ganymede’s interior EXCEPT

The word “Extensive” in the passage is closest in meaning to

Paragraph 5 supports each of the following statements about Ganymede EXCEPT:

According to paragraph 6, the differences in how Callisto and Ganymede evolved are most probably due to differences in their

Look at the four squares  that indicate where the following sentence could be added to the passage. The differences between Ganymede and Callisto, however, extend much further below the surface of the satellites.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.

Directions: Select from the seven sentences below the two sentences that are true of Callisto and the three sentences that are true of Ganymede. Drag each sentence you select into the appropriate column of the table. Two of the sentences will NOT be used. This question is worth 3 points.

Callisto and Ganymede From 1996 to 1999, the Galileo spacecraft passed through the Jovian system, providing much information about Jupiter’s satellites. Callisto, the outermost of Jupiter’s four largest satellites, orbits the planet in seventeen days at a distance from Jupiter of two million kilometers. Like our own Moon, Callisto rotates in the same period as it revolves, so it always keeps the same face toward Jupiter. Its noontime surface temperature is only about −140ºC, so water ice is stable on its surface year-round. Callisto has a diameter of 4,820 kilometers, almost the same as that of Mercury. Its mass is only one-third as great, which means its density must be only one-third as great as well. This tells us that Callisto has far less of the rocky metallic materials found in the inner planets and must instead be an icy body through much of its interior. Callisto has not fully differentiated, meaning separated into layers of different density materials. Astronomers can tell that it lacks a dense core from the details of its gravitational pull on the Galileo spacecraft during several very close flybys. This fact surprised scientists, who expected that all the big icy moons would be differentiated. It is much easier for an icy body to differentiate than for a rocky one, since the melting temperature of ice is so low. Only a little heating will soften the ice and get the process started, allowing the rock and metal to sink to the center and the slushy ice to float to the surface. Yet Callisto seems to have frozen solid before the process of differentiation was complete. Like our Moon’s highlands, the surface of Callisto is covered with impact craters. The survival of these craters tells us that an icy object can form and retain impact craters in its surface. In thinking of ice so far from the Sun, it is important not to judge its behavior from that of the much warmer ice we know on Earth; at the temperatures of the outer solar system, ice on the surface is nearly as hard as rock, and behaves similarly. Ice on Callisto does not deform or flow like ice in glaciers on Earth. Callisto is unique among the planet-sized objects of the solar system in its absence of interior forces to drive geological evolution. The satellite was born dead and has remained geologically dead for more than four billion years. Ganymede, another of Jupiter’s satellites and the largest in our solar system, is also cratered, but less so than Callisto.  About one-quarter of its surface seems to be as old and heavily cratered; the rest formed more recently, as we can tell by the sparse covering of impact craters as well as the relative freshness of the craters.  Ganymede is a differentiated world, like the terrestrial planets.  Measurements of its gravity field tell us that the rock and metal sank to form a core about the size of our Moon, with a mantle and crust of ice floating above it.  In addition, the Galileo spacecraft discovered that Ganymede has a magnetic field, the signature of a partially molten interior. Ganymede is not a dead world, but rather a place of continuing geological activity powered by an internal heat source. Much of its surface may be as young as half a billion years. The younger terrain is the result of tectonic and volcanic forces. Some features formed when the crust cracked, flooding many of the craters with water from the interior. Extensive mountain ranges were formed from compression of the crust, forming long ridges with parallel valleys spaced one to two kilometers apart. In some places older impact craters were split and pulled apart. There are even indications of large-scale crustal movements that are similar to the plate tectonics of Earth. Why is Ganymede different from Callisto? Possibly the small difference in size and internal heating between the two led to this divergence in their evolution. But more likely the gravity of Jupiter is to blame for Ganymede’s continuing geological activity. Ganymede is close enough to Jupiter that tidal forces from the giant planet may have episodically heated its interior and triggered major convulsions on its crust.