Callisto and Ganymede
学韩语From 1996 to 1999, the Galileo spacecraft pasd through the Jovian system, providing much information about Jupiter's satellites. Callisto, the outermost of Jupiter's four largest satellites, orbits the planet in venteen 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.
According to paragraph 1, which of the following statements about Callisto is true?
A rareIt is the satellite clost to Jupiter's surface.
B 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 venteen days.
According to paragraph 1, how do scientists know that Callisto is made up largely of ice?
A A sample of its interior was taken by the Galileo spacecraft in the late 1990s.
B It has too low a density to contain much rocky metallic material. motel是什么意思
C With a noontime surface temperature of only about -140° C, the ice on it never melts.
D All of the bodies in the Jovian system are icy, becau they are so far from the Sun.
Callisto has not fully differentiated, meaning parated into layers of different density materials. Astronomers can tell that it lacks a den core from the details of its gravitational pull on the Galileo spacecraft during veral very clo flybys. This fact surprid 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 temper
ature 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 ems to have frozen solid before the process of differentiation was complete.
Why does the author provide the information that "It is much easier for an icy body to differentiate than for a rocky one"?
动员大会主持词
A 中韩互译在线翻译器To support the claim that all of the big icy moons are differentiated
B To suggest that Callisto may be a rocky body rather than an icy one
ferreC To explain why scientists expected Callisto to be differentiated
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D To refute the claim that Callisto could not differentiate becau it was frozen solid
All of the following questions are answered in paragraph 2 EXCEPT:
A Why was Callisto frozen solid before differentiation was complete?
B What allows the process of differentiation to get started?
C Why is it easier for an icy body to differentiate than a rocky one?
D How do astronomers know that Callisto lacks a den core?
Like our Moon's highlands, the surface of Callisto is covered with impact craters. The survival of the 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 abnce of interior forces to drive geological evolution. The satellite was born dead and has remained geologically dead for more than four billion years.
Which of the ntences below best express the esntial information in the highlighted
ntence in the passage? Incorrect choices change the meaning in important ways or leave out esntial information.
A It should not be assumed that surface ice has the same characteristics wherever it is found.
B Surface ice and rock are much more similar in temperature in the outer solar system than they are on Earth.
C The further away surface ice is from the Sun, the more its temperature differs from that of the warmer ice on Earth.
D In the cold of the outer solar system, surface ice is so hard it behaves more like rock than like the warmer ice on Earth.
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 ems to be as old and heavily cratered; the rest formed more recently, as we can tell by the spar 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 word "signature" in the passage is clost in meaning to
A primary cau
muranoB end result
C identifying mark
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D by-product
According to paragraph 4, each of the following provides evidence about Ganymede's interior EXCEPT
A Ganymede's large size
B measurements of Ganymede's gravity field
C 成都o培训the fact that Ganymede has a magnetic field
D the fact that Ganymede continues to be geologically active
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.
