How the solar system Was Formed

Any model of the origin of the solar system must explain why all the planets orbit the Sun in the same direction and in nearly the same plane. One model that was devised explicitly to address this issue was the tidal hypothesis, proposed in the early 1900s.Two nearby planets, stars, or galaxies exert varying gravitational, or tidal, forces on each other that cause the objects to elongate. In the tidal hypothesis, another star happened to pass close by the Sun, and the star’s tidal forces drew a long filament (threadlike formation of matter) out of the Sun. The filament material then went into orbit around the Sun, and all of it naturally orbited in the same direction and in the same plane. From this filament of material the planets condensed. However, it was shown in the 1930s that tidal forces strong enough to pull a filament out of the Sun would cause the filament to disperse before it could condense into planets.

An entirely different model is now thought to describe the most likely series of events that led to our present solar system. The central idea of this model dates to the late 1700s, when the German philosopher Immanuel Kant and the French scientist Pierre-Simon Laplace turned their attention to the manner in which the planets orbit the Sun. Both concluded that the arrangement of the orbits-all in the same direction and in nearly the same plane—could not be a mere coincidence. To explain the orbits, Kant and Laplace independently proposed that our entire solar system, including the Sun as well as all of its planets and satellites, formed from a vast, flat, rotating cloud of gas and dust called the solar nebula. This model is called the nebular hypothesis.

The consensus among today’s astronomers is that Kant and Laplace were exactly right. In the modern version of the nebular hypothesis, at the outset the solar nebula had a mass greater than that of our present-day Sun. Because each part of the nebula exerted a gravitational attraction on the other parts, matter at the perimeter was pulled toward the center. whereas matter in the center, because it was pulled equally from each side, did not move at all, and thus the nebula contracted with the greatest concentration of matter occurring in a central region called the protosun. As its name suggests, this part of the solar nebula eventually developed into the Sun. The planets formed from the much sparser material in the outer regions of the solar nebula. As a result, the mass of all the planets together is only 0.1 percent of the Sun’s mass.

When you drop a ball, the gravitational attraction of Earth makes the ball fall faster and faster as it falls; in the same way, material falling inward toward the protosun gained speed. As this fast-moving material ran into the protosun, the energy of the collision was converted into thermal energy, causing the temperature deep inside the protosun to climb. This process, in which the gravitational energy of a contracting gas cloud is converted into thermal energy, is called Kelvin-Helmholtz contraction, after the nineteenth-century physicists who first described it.

As the newly created protosun continued to contract and become denser, its temperature continued to climb as well. After about 100,000 years, the protosun’s surface temperature stabilized at about 6,000 Kelvins, but the temperature in its interior kept increasing to ever-higher values as the central regions of the protosun became denser and denser. Eventually, after perhaps10 million years had passed since the solar nebula first began to contract, the matter at the center of the protosun reached a density about 100 times greater than water, and a temperature of a few million Kelvins. Under these extreme conditions, nuclear reactions that convert hydrogen into helium began in the protosun’s interior. When this happened, the energy released by these reactions stopped the contraction, and a large amount of light energy was radiated into space. The protosun had become a star. Nuclear reactions continue to the present day in the interior of the Sun and are the source of all the energy that the Sun radiates into space.

 

1

Any model of the origin of the solar system must explain why all the planets orbit the Sun in the same direction and in nearly the same plane. One model that was devised explicitly to address this issue was the tidal hypothesis, proposed in the early 1900s.Two nearby planets, stars, or galaxies exert varying gravitational, or tidal, forces on each other that cause the objects to elongate. In the tidal hypothesis, another star happened to pass close by the Sun, and the star’s tidal forces drew a long filament (threadlike formation of matter) out of the Sun. The filament material then went into orbit around the Sun, and all of it naturally orbited in the same direction and in the same plane. From this filament of material the planets condensed. However, it was shown in the 1930s that tidal forces strong enough to pull a filament out of the Sun would cause the filament to disperse before it could condense into planets.

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

• Ademonstrated
• Bapproved
• Cdiscussed
• Ddesigned

2

Any model of the origin of the solar system must explain why all the planets orbit the Sun in the same direction and in nearly the same plane. One model that was devised explicitly to address this issue was the tidal hypothesis, proposed in the early 1900s.Two nearby planets, stars, or galaxies exert varying gravitational, or tidal, forces on each other that cause the objects to elongate. In the tidal hypothesis, another star happened to pass close by the Sun, and the star’s tidal forces drew a long filament (threadlike formation of matter) out of the Sun. The filament material then went into orbit around the Sun, and all of it naturally orbited in the same direction and in the same plane. From this filament of material the planets condensed. However, it was shown in the 1930s that tidal forces strong enough to pull a filament out of the Sun would cause the filament to disperse before it could condense into planets.

According to paragraph 1, the tidal hypothesis proposed that the planets formed when

• Amaterial from a nearby galaxy was pulled into orbit around the sun
• Bmatter condensed from a filament of material pulled from the sun
• Cthe tidal motion of the Sun caused nearby matter to condense
• Dmatter orbiting in different planes was pulled by tidal forces into nearly the same plane

3

An entirely different model is now thought to describe the most likely series of events that led to our present solar system. The central idea of this model dates to the late 1700s, when the German philosopher Immanuel Kant and the French scientist Pierre-Simon Laplace turned their attention to the manner in which the planets orbit the Sun. Both concluded that the arrangement of the orbits-all in the same direction and in nearly the same plane—could not be a mere coincidence. To explain the orbits, Kant and Laplace independently proposed that our entire solar system, including the Sun as well as all of its planets and satellites, formed from a vast, flat, rotating cloud of gas and dust called the solar nebula. This model is called the nebular hypothesis.

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

• Avisible
• Bhuge
• Cdistant
• Dfast

4

The consensus among today’s astronomers is that Kant and Laplace were exactly right. In the modern version of the nebular hypothesis, at the outset the solar nebula had a mass greater than that of our present-day Sun. Because each part of the nebula exerted a gravitational attraction on the other parts, matter at the perimeter was pulled toward the center. whereas matter in the center, because it was pulled equally from each side, did not move at all, and thus the nebula contracted with the greatest concentration of matter occurring in a central region called the protosun. As its name suggests, this part of the solar nebula eventually developed into the Sun. The planets formed from the much sparser material in the outer regions of the solar nebula. As a result, the mass of all the planets together is only 0.1 percent of the Sun’s mass.

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.

• AThe protosun was a region of dense matter at the center of the nebula that exerted a gravitational pull on the other parts of the nebula.
• BThe contraction of the nebula caused its parts to exert gravitational pull on each other, causing most of the matter to concentrate in a dense region at its center called the protosun.
• CGravitational attraction between its parts caused the nebula to contract and form a dense region at its center called the protosun.
• DThe region with the greatest concentration was formed when the protosun exerted a gravitational pull on the other parts of the nebula.

5

An entirely different model is now thought to describe the most likely series of events that led to our present solar system. The central idea of this model dates to the late 1700s, when the German philosopher Immanuel Kant and the French scientist Pierre-Simon Laplace turned their attention to the manner in which the planets orbit the Sun. Both concluded that the arrangement of the orbits-all in the same direction and in nearly the same plane—could not be a mere coincidence. To explain the orbits, Kant and Laplace independently proposed that our entire solar system, including the Sun as well as all of its planets and satellites, formed from a vast, flat, rotating cloud of gas and dust called the solar nebula. This model is called the nebular hypothesis.

The consensus among today’s astronomers is that Kant and Laplace were exactly right. In the modern version of the nebular hypothesis, at the outset the solar nebula had a mass greater than that of our present-day Sun. Because each part of the nebula exerted a gravitational attraction on the other parts, matter at the perimeter was pulled toward the center. whereas matter in the center, because it was pulled equally from each side, did not move at all, and thus the nebula contracted with the greatest concentration of matter occurring in a central region called the protosun. As its name suggests, this part of the solar nebula eventually developed into the Sun. The planets formed from the much sparser material in the outer regions of the solar nebula. As a result, the mass of all the planets together is only 0.1 percent of the Sun’s mass.

According to paragraphs 2 and 3, all of the following describe a feature of the nebular hypothesis EXCEPT:

• AThe solar system formed from a cloud of gas and dust.
• BThe solar nebula was massive compared to today’s Sun.
• CThe planets formed from the less-dense parts of the solar nebula.
• DThe rotation of the solar nebula forced most of its mass to its outer edges.

6

When you drop a ball, the gravitational attraction of Earth makes the ball fall faster and faster as it falls; in the same way, material falling inward toward the protosun gained speed. As this fast-moving material ran into the protosun, the energy of the collision was converted into thermal energy, causing the temperature deep inside the protosun to climb. This process, in which the gravitational energy of a contracting gas cloud is converted into thermal energy, is called Kelvin-Helmholtz contraction, after the nineteenth-century physicists who first described it.

Why does the author provide the information that “When you drop a ball, the gravitational attraction of Earth makes the ball fall faster and faster as it falls”?

• ATo help explain what happened to material pulled toward the protosun
• BTo provide evidence that gravity causes falling objects to move faster as they near Earth
• CTo contrast the effects of gravity on Earth with those on the protosun
• DTo help explain why fast-moving matter tends to condense into around mass

7

When you drop a ball, the gravitational attraction of Earth makes the ball fall faster and faster as it falls; in the same way, material falling inward toward the protosun gained speed. As this fast-moving material ran into the protosun, the energy of the collision was converted into thermal energy, causing the temperature deep inside the protosun to climb. This process, in which the gravitational energy of a contracting gas cloud is converted into thermal energy, is called Kelvin-Helmholtz contraction, after the nineteenth-century physicists who first described it.

According to paragraph 4, which of the following best describes Kelvin-Helmholtz contraction?

• AAn increase in thermal energy inside a gas cloud causes the cloud to contract rapidly.
• BAs a gas cloud contracts, its gravitational energy is changed into heat energy.
• CA moving cloud of gas exerts gravitational energy that attracts nearby matter.
• DAn increase in the speed of matter falling into a gas cloud causes the cloud to contract.

8

As the newly created protosun continued to contract and become denser, its temperature continued to climb as well. After about 100,000 years, the protosun’s surface temperature stabilized at about 6,000 Kelvins, but the temperature in its interior kept increasing to ever-higher values as the central regions of the protosun became denser and denser. Eventually, after perhaps10 million years had passed since the solar nebula first began to contract, the matter at the center of the protosun reached a density about 100 times greater than water, and a temperature of a few million Kelvins. Under these extreme conditions, nuclear reactions that convert hydrogen into helium began in the protosun’s interior. When this happened, the energy released by these reactions stopped the contraction, and a large amount of light energy was radiated into space. The protosun had become a star. Nuclear reactions continue to the present day in the interior of the Sun and are the source of all the energy that the Sun radiates into space.

Paragraph 5 implies which of the following about today’s Sun?

• AThe Sun continues to contract and increase in density.
• BThe amount of hydrogen in the interior of the Sun continues to decrease.
• CThe Sun radiates less light energy today than at the time it was formed.
• DThe interior of the Sun is about the same temperature as the surface.

9

Look at the four squaresthat indicate where the following sentence could be added to the passage

Consequently, they attempted to find some cause for the fact that all the planets had orbits that shared these two features.

Where would the sentence best fit？Click on a square  sentence to the passage.

10

Scientists have attempted to develop models that describe how our solar system formed.

• AAccording to the tidal-hypothesis model, the planets condensed from material pulled out of the Sun by the gravitational force from a passing star.
• BAccording to the nebular-hypothesis model, the solar system originated as a rotating cloud of gas and dust that heated and contracted into the Sun and planets.
• CThe Sun was formed when nuclear reactions in the interior of the protosun caused contraction of the protosun to stop and light energy to radiate into space.
• DThe tidal-hypothesis model fails to explain why the planets have remained in the same orbit even after the original tidal forces ended.
• EThe nebular-hypothesis model proposes that the solar system formed when nuclear reactions in the Sun released material that later cooled.
• FThe direction and position of the orbits of the planets around the Sun is determined by the combined effect of the gravitational forces between all parts of the solar system.

 

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