TPO42阅读文本及答案解析

Callisto and Ganymede

From 1996 to 1999, the Galileo spacecraft passed through the Joviansystem, providing much information about Jupiter's satellites. Callisto, theoutermost of Jupiter's four largest satellites, orbits the planet in seventeendays 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 sameface toward Jupiter. Its noontime surface temperature is only about -140°C, sowater ice is stable on its surface year-round. Callisto has a diameter of 4.820kilometers, almost the same as that of Mercury. Its mass is only one-third asgreat, which means its density must be only one-third as great as well. Thistells us that Callisto has far less of the rocky metallic materials found inthe inner planets and must instead be an icy body through much of its interior.

Callisto has not fully differentiated, meaning separated into layersof different density materials. Astronomers can tell that it lacks a dense corefrom the details of its gravitational pull on the Galileo spacecraft duringseveral very close flybys. This fact surprised scientists, who expected thatall the big icy moons would be differentiated. It is much easier for an icybody to differentiate than for a rocky one, since the melting temperature ofice is so low. Only a little heating will soften the ice and get the processstarted, allowing the rock and metal to sink to the center and the slushy iceto float to the surface. Yet Callisto seems to have frozen solid before theprocess of differentiation was complete.

Like our Moon's highlands, the surface of Callisto is covered with impactcraters. The survival of these craters tells us that an icy object can form andretain impact craters m its surface. In thinking of ice so far from the Sun, itis important not to judge its behavior from that of the much warmer ice we knowon Earth; at the temperatures of the outer solar system, ice on the surface isnearly as hard as rock, and behaves similarly. Ice on Callisto does not deformor flow like ice in glaciers on Earth. Callisto is unique among the planet-sizedobjects of the solar system in its absence of interior forces to drivegeological evolution. The satellite was born dead and has remained geologicallydead for more than four billion years.

Ganymede, another of Jupiter's satellites and the largest in oursolar system, is also cratered, but less so than Callisto. About one-quarter ofits surface seems to be as old and heavily cratered; the rest formed morerecently, as we can tell by the sparse covering of impact craters as well asthe relative freshness of the craters. Ganymede is a differentiated world, likethe terrestrial planets. Measurements of its gravity field tell us that therock and metal sank to form a core about the size of our Moon, with a mantleand crust of ice floating above it. In addition, the Galileo spacecraft discoveredthat Ganymede has a magnetic field, the signature of a partially molteninterior. Ganymede is not a dead world, but rather a place of continuinggeological activity powered by an internal heat source. Much of its surface maybe as young as half a billion years.

The younger terrain is the result of tectonic and volcanic forcesSome features formed when the crust cracked, flooding many of the craters withwater from the interior. Extensive mountain ranges were formed from compressionof the crust, forming long ridges with parallel valleys spaced one to twokilometers apart. In some places older impact craters were split and pulledapart. There are even indications of large-scale crustal movements that aresimilar to the plate tectonics of Earth.

 Why is Ganymede differentfrom Callisto? Possibly the small difference in size and internal heatingbetween the two led to this divergence in their evolution. But more likely thegravity of Jupiter is to blame for Ganymede's continuing geological activity.Ganymede is close enough to Jupiter that tidal forces from the giant planet mayhave episodically heated its interior and triggered major convulsions on itscrust.

paragraph 1

 From 1996 to 1999, theGalileo spacecraft passed through the Jovian system, providing much informationabout Jupiter's satellites. Callisto, the outermost of Jupiter's four largestsatellites, orbits the planet in seventeen days at a distance from Jupiter oftwo million kilometers. Like our own Moon. Callisto rotates in the same periodas it revolves, so it always keeps the same face toward Jupiter. Its noontimesurface temperature is only about -140°C, so water ice is stable on its surfaceyear-round. Callisto has a diameter of 4.820 kilometers, almost the same asthat of Mercury. Its mass is only one-third as great, which means its densitymust be only one-third as great as well. This tells us that Callisto has farless of the rocky metallic materials found in the inner planets and mustinstead be an icy body through much of its interior.

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

It is the satellite closest to Jupiter's surface

Its surface temperature is constant at all times of the day.

C. It has the same mass and diameter as the planet Mercury

D. It completes one rotation every seventeen days.

2. According to paragraph 1, how do scientists know that Callisto ismade up largely of ice?

A. A sample of its interior was taken by the Galileo spacecraft inthe late 1990s

B. It has too low a density to contain much rocky metallic material

C. With a noontime surface temperature of only about .140° C. theice on it never melts

D. All of the bodies in the Jovian system are icy, because they areso far from the Sun.

paragraph 2

Callisto has not fully differentiated, meaning separated into layersof different density materials. Astronomers can tell that it lacks a dense corefrom the details of its gravitational pull on the Galileo spacecraft duringseveral very close flybys. This fact surprised scientists, who expected thatall the big icy moons would be differentiated. It is much easier for an icybody to differentiate than for a rocky one, since the melting temperature ofice is so low. Only a little heating will soften the ice and get the processstarted, allowing the rock and metal to sink to the center and the slushy iceto float to the surface. Yet Callisto seems to have frozen solid before theprocess of differentiation was complete.

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

A. To support the claim that all of the big icy moons aredifferentiated

B. To suggest that Callisto may be a rocky body rather than an icyone

C. To explain why scientists expected Callisto to be differentiated

D. To refute the claim that Callisto could not differentiate becauseit was frozen solid

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

Why was Callisto frozen solid before differentiation was complete?

What allows the process of differentiation to get started?

C. Why is it easier for an icy body to differentiate than a rockyone?

D. How do astronomers know that Callisto lacks a dense core?

paragraph 3

Like our Moon's highlands, the surface of Callisto is covered withimpact craters. The survival of these craters tells us that an icy object canform and retain impact craters m its surface. In thinking of ice so far fromthe Sun, it is important not to judge its behavior from that of the much warmerice we know on Earth; at the temperatures of the outer solar system, ice on thesurface is nearly as hard as rock, and behaves similarly. Ice on Callisto doesnot deform or flow like ice in glaciers on Earth. Callisto is unique among theplanet-sized objects of the solar system in its absence of interior forces to drivegeological evolution. The satellite was born dead and has remained geologicallydead for more than four billion years.

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

A. It should not be assumed that surface ice has the samecharacteristics wherever it is found

B. Surface ice and rock are much more similar in temperature in theouter solar system than they are on Earth.

C. The further away surface ice is from the Sun, the more itstemperature differs from that of the warmer ice on Earth

D. In the cold of the outer solar system, surface ice is so hard itbehaves more like rock than like the warmer ice on Earth

6.According to paragraph 3, how is Callisto different from all otherplanet-sized objects in the solar system?

A. It can form and retain impact craters on its icy surface

B. It has ice glaciers that do not flow or deform.

C. It has never had the interior forces required for geologicalevolution.

D. It is more than four billion years old.

paragraph 4

Ganymede, another of Jupiter's satellites and the largest in oursolar system, is also cratered, but less so than Callisto. About one-quarter ofits surface seems to be as old and heavily cratered; the rest formed morerecently, as we can tell by the sparse covering of impact craters as well asthe relative freshness of the craters. Ganymede is a differentiated world, likethe terrestrial planets. Measurements of its gravity field tell us that therock and metal sank to form a core about the size of our Moon, with a mantleand crust of ice floating above it. In addition, the Galileo spacecraftdiscovered that Ganymede has a magnetic field, the signature of a partiallymolten interior. Ganymede is not a dead world, but rather a place of continuinggeological activity powered by an internal heat source. Much of its surface maybe as young as half a billion years.

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

primary cause

end result

identifying mark

by-product

8. According to paragraph 4, each of the following provides evidenceabout Ganymede's interior EXCEPT

A. Ganymede's large size

B. measurements of Ganymede's gravity field

C. the fact that Ganymede has a magnetic field

D. the fact that Ganymede continues to be geologically active

paragraph 5

The younger terrain is the result of tectonic and volcanic forcesSome features formed when the crust cracked, flooding many of the craters withwater from the interior. Extensive mountain ranges were formed from compressionof the crust, forming long ridges with parallel valleys spaced one to twokilometers apart. In some places older impact craters were split and pulledapart. There are even indications of large-scale crustal movements that aresimilar to the plate tectonics of Earth.

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

Unusual

Large

New

Steep

10. Paragraph 5 supports each of the following statements aboutGanymede EXCEPT:

A. All water on it has always been frozen solid.

B. There is evidence that part of its crust once broke open

C. Its crust has been subject to forces that have created mountainsand valleys.

D. Some of its older craters have been split apart by more recentgeological activity

paragraph 6

Why is Ganymede different from Callisto? Possibly the smalldifference in size and internal heating between the two led to this divergencein their evolution. But more likely the gravity of Jupiter is to blame forGanymede's continuing geological activity. Ganymede is close enough to Jupiterthat tidal forces from the giant planet may have episodically heated itsinterior and triggered major convulsions on its crust.

11. According to paragraph 6, the differences in how Callisto andGanymede evoked are most probably due to differences in their

A. size and internal heating

B. distance from Jupiter

C. chemical and physical composition

D. age

Look at the four squares  [■]  that indicate where the following sentencecould be added to the passage.

The difference between Ganymede and Callisto, however, extend much further below thesurface of the satellites.

Where would the sentence best fit? Click on square [■] to add thesentence to the passage

Ganymede, another of Jupiter's satellites and the largest in oursolar system, is also cratered, but less so than Callisto. [■] Aboutone-quarter of its surface seems to be as old and heavily cratered; the restformed more recently, as we can tell by the sparse covering of impact cratersas well as the relative freshness of the craters. [■] Ganymede is adifferentiated world, like the terrestrial planets. [■] Measurements of itsgravity field tell us that the rock and metal sank to form a core about thesize of our Moon, with a mantle and crust of ice floating above it. [■] Inaddition, the Galileo spacecraft discovered that Ganymede has a magnetic field,the signature of a partially molten interior. Ganymede is not a dead world, butrather a place of continuing geological activity powered by an internal heatsource. Much of its surface may be as young as half a billion years.

13. Directions:An introductory sentence for a brief summary of thepassage is provided below. Complete the summary by selected THREE answerchoices that express the most important ideas in the passage.Some sentences donot belong in the summary because they express ideas that are not presented inthe passage or are minor ideas in the passage.This question is worth 2 points.

 Drag your choices to thespaces where they belong. To review the passage, click on View Text

Between 600 B.C. and 450 B.C., Athens changed the distribution ofpolitical power between the aristocracy and ordinary citizens.

Callisto

Ganymede

阅读三

Answer Choices

A. It has a core that consists mainly of rock and metal.

B. It may have formed as recently as half a billion years ago

C. Its interior is not fully solid

D. Its evolution has probably been strongly influenced by Jupiter'sgravity

E. It always keeps the same face toward Jupiter as it orbits theplanet

F. Its crust is covered by slow-moving glaciers

G. Its entire surface is heavily cratered