Comets-small bodies of ice and dust that orbit the Sun are perishable objects. A comet that passes by the Sun many times will eventually lose all of its ice due to the heat and become a small rock. Other comets are lost because they literally fall into the Sun The SOHO and STEREO spacecraft (which monitor the Sun) have revealed images of dozens per year falling into the Sun. Since there continue to be comets 4.5 billion years after the solar system formed, there must be a huge source of comets somewhere far from the Sun.
1.The word “literally”in the passage is closest in meaning to
A.actually
B.finally
C.completely
D.suddenly
Based on the portion of comets’ orbits that can be observed, astronomers can calculate their starting point.The majority of comets follow orbits that indicate their outermost distance from the Sun is more than 50,000 AU(one AU, or astronomical unit, equals about 150 million kilometers). At the same time, only a few appear to have speeds that would carry them completely beyond the Sun’s gravitational influence into the vicinity of a neighboring star, so the comet reservoir must be in a very distant part of the solar system, Comets enter the inner solar system from all directions without any clear preference. so this great swarm of comets must be roughly spherical.
2.The word ” preference”in the passage is closest in meaning to
A.limit
B.tendency
C.source
D.effect
3.In paragraph 2, why does the author discuss the outer most distance from the Sun at which comets orbit?
A.To support the idea that comets originate in a faraway part of the solar system
B.To emphasize the high speeds at which some comets orbit
C.To demonstrate that comets are influenced by various gravitational forces
D.To explain why comets enter the inner solar system from all directions
4.According to paragraph 2, all of the following are true of the majority of comets EXCEPT:
A.Their orbits take them 50,000 AU or more from the Sun.
B.They remain within the Sun’s gravitational influence.
C.They orbit around a neighboring star of the Sun.
D.They come from a sphere-shaped grouping of comets.
This kind of reasoning was used by Dutch astronomer Jan Oort to propose the existence of a vast cloud of trillions of icy bodies orbiting far, far beyond the planets, Known today as the Oort cloud, astronomers think it formed from material in the original solar nebula (a cloud of gas and dust from which the Sun and the planets formed), or perhaps from material orbiting neighboring stars that formed together with the Sun, since we normally see stars forming in clusters of hundreds or thousands. Some comets may be made of material that originally orbited near the giant planets (Jupiter, Saturn, Uranus, and Neptune) and was tossed into the outer parts of the solar system by the gravitational force of those planets.
5.In paragraph 3, which of the following is NOT mentioned as a way in which the Oort cloud and its comets may have formed?
A.The Oort cloud formed from the same cloud of dust and gas as the Sun and planets.
B.The Oort cloud formed from materials orbiting stars nearby the early Sun.
C.The Oort cloud formed from the destruction of large clusters of stars.
D.The Oort cloud formed from materials thrown toward the outer solar system by the giant planets.
▉Astronomers suspect that the gravitational influence of stars neighboring the solar system may alter the orbits of bodies in the Oort cloud occasionally, causing some to drop in toward the inner solar system.▉ A single disturbance may shift enough orbits to supply comets to the inner solar system for tens of thousands of years.▉The discovery of massive objects such as the dwarf planet Sedna suggests that comets may also be disturbed by dwarf planets that orbit in the Oort cloud.▉Comets from the Oort cloud may take millions of years to complete an orbit and are therefore known as long period comets, With orbits so far from the Sun, these icy bodies receive virtually no solar heating, and calculations indicate that their temperature when so far from the Sun is a mere -270°C Thus, their gases and ices remain deeply frozen.
6.According to paragraph 4, which of the following causes comets in the Oort cloud to drop into the inner solar system?
A.Changes in the orbits of comets caused by stars and dwarf planets
B.Disturbances caused by dwarf planets falling into the Oort cloud
C.Slight changes to the orbits of objects in the inner solar system
D.Changes to the temperature of bodies in the Oort cloud as they move closer to the Sun
Some comets reappear at intervals of less than 200years. These short-period comets include Halley’s, which has a period of 76 years. These comets come mostly from a flatter, less remote region-the Kuiper belt. The Kuiper belt begins near the orbit of Neptune, 30 AU from the Sun, and seems to thin out near 55 AU from the Sun,but its outer boundary is uncertain. Many much larger bodies, such as Pluto, Eris, and other dwarf planets, also orbit in the Kuiper belt. Their gravitational interactions may be what sends smaller bodies in the Kuiper belt into the inner solar system to become comets. The origin of short-period comets is still under study. At one time it was thought that they began in the Oort cloud, and that their orbits were altered as they moved by one of the giant planets. Many astronomers now suspect that most short-period comets came originally from the Kuiper belt.because most of their orbits lie close to the plane of the solar system and orbit in the same direction as the rest of the solar system. Comet Wild 2 was probably a Kuiper belt object originally. It was deflected into the inner solar system in 1974 during a close passage by Jupiter and now has an orbital period of just 6 years.
7.According to paragraphs 4 and 5, long-period and short-period comets differ in which of the following ways?
A.Their size
B.How close they come to the Sun
C.How much time they take to complete an orbit
D.How long ago they began to orbit the Sun
8.Paragraph 5 suggests that which of the following hypotheses about short-period comets is no longer believed to be true?
A.Short-period comets began in the Oort cloud
B.Short-period comets enter the inner solar system from the Kuiper belt.
C.Short-period comets came from the same general area as Pluto and Eris.
D.Short-period comets orbit in the same direction as the solar system.
9.Look at the four squares [▊] that indicate where the following sentence could be added to the passage.Where would the sentence best fit?
These changes need not be large to have a big impact.
10.Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
The continued presence of comets in the solar system suggests that there is a huge source of comets far from the Sun.
The SOHO and STEREO spacecraft have provided images of comets tha have allowed astronomers o clearly see the entire path of their orbits rather than just a part.
Comets have different orbital periods from one another, and the amount of ice they retain varies depending on how often they pass close to the Sun during their orbits.
Information about the speed and orbits of the comets and their direction of entry into the solar system led the astronomer Oort to conclude they came from a cloud of icy bodies far from the planets.
The orbits of comets that originate in the Oort cloud may be influenced by objects outside the solar system, and comets from the Kuiper belt orbit in the same direction as the rest of the solar system.
Some comets orbit near giant planets while others orbit near dwarf planets, and those that orbit near dwarf planets reappear at greater intervals than those that orbit near giant planets.
Astronomers have used comets such as Halley’s and Wild 2to suggest that most long-period comets came from the Kuper belt while most short-period comets originated in the Oort cloud.
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