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Reading
The Formation of Planetary Systems
astronomyphysical science語彙
難しい
Reading
The Formation of Planetary Systems
astronomyphysical science語彙
難しい
Paragraph 1
The prevailing scientific model for the formation of our solar system and other planetary systems is the nebular hypothesis. This theory posits that a solar system begins as a vast, rotating cloud of interstellar gas and dust, known as a solar nebula. Under the influence of its own gravity, this cloud begins to collapse. As it contracts, the law of conservation of angular momentum dictates that its rotation must speed up, much like an ice skater pulling in their arms. This accelerated rotation causes the cloud to flatten into a spinning protoplanetary disk. The vast majority of the mass, primarily hydrogen and helium, collapses into the center, becoming increasingly hot and dense. Eventually, the temperature and pressure at the core become so extreme that nuclear fusion ignites, and a new star—a protostar—is born.
Paragraph 2
While the protostar forms at the center, the rest of the material in the protoplanetary disk is not idle. This disk is a cosmic nursery where planets are built through a process called accretion. Initially, tiny dust grains, composed of rock, ice, and metal, collide and stick together due to electrostatic forces. Over millions of years, these small clumps grow into pebble-sized objects, then boulder-sized planetesimals. As these planetesimals grow larger, their gravitational pull increases, allowing them to attract more material and smaller planetesimals at an ever-increasing rate. This runaway growth leads to the formation of protoplanets, bodies that can be as large as Mars or the Moon. The accretion process is not gentle; it is characterized by countless violent collisions.
Paragraph 3
The composition of the planets that form is largely determined by their distance from the central protostar. The region near the star is extremely hot, so only materials with high melting points, such as metals (iron, nickel) and silicates (rock), can condense into solid form. This explains the formation of the small, dense, terrestrial planets—Mercury, Venus, Earth, and Mars—in the inner solar system. Beyond a certain point, known as the frost line or snow line, temperatures are cold enough for volatile compounds like water, ammonia, and methane to freeze into solid ice grains. This is the realm of the gas giants and ice giants. Because ice is far more abundant in the protoplanetary disk than rock and metal, the protoplanets that formed beyond the frost line could grow much larger, much more quickly.
Paragraph 4
The massive cores of the outer protoplanets, rich in ice, exerted a powerful gravitational pull. This allowed them to capture vast amounts of the most abundant elements in the nebula—hydrogen and helium gas—before the solar wind from the young star blew the remaining gas out of the system. This rapid accumulation of gas created the enormous, low-density planets we know as Jupiter and Saturn. The more distant ice giants, Uranus and Neptune, were less successful in this gas-capture phase, likely because the nebula was less dense at their greater distance and they formed more slowly. Consequently, they are composed primarily of the original ice and rock from their cores with much thinner hydrogen and helium atmospheres. The entire process of clearing the disk, from the initial collapse to the final formation of stable planets, is thought to take a few hundred million years.
Paragraph 5
The final stage of planet formation is a period of dynamic instability and cleanup. The gravitational influence of the newly formed giant planets can send remaining planetesimals and protoplanets scattering throughout the solar system. Some are ejected into interstellar space, while others are sent careening into the inner solar system, leading to a period known as the Late Heavy Bombardment. This era of intense impacts is what created many of the craters we see on the Moon and other terrestrial bodies today. The asteroid belt, located between Mars and Jupiter, is thought to be the remnant of a protoplanet that was prevented from fully forming by the immense gravitational perturbations of Jupiter. Over time, the orbits stabilize, and the solar system settles into the relatively orderly configuration we observe today.
The word 'prevailing' in paragraph 1 is closest in meaning to...
The word 'perturbations' in paragraph 5 is closest in meaning to...
According to paragraph 1, why does a collapsing solar nebula spin faster?
What is the significance of the 'frost line' as described in paragraph 3?
What can be inferred from paragraph 4 about Jupiter compared to Neptune?
In paragraph 1, why does the author mention 'an ice skater pulling in their arms'?
What does the author imply about the asteroid belt in paragraph 5?
According to the passage, the terrestrial planets are composed mainly of rock and metal because...
Look at the four squares [■] that indicate where the following sentence could be added to paragraph 3. Where would the sentence best fit?
This temperature gradient created a fundamental division in the types of materials available for planet building.
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.
According to the nebular hypothesis, planetary systems form from the collapse of a gas and dust cloud, with planets being built through a process of accretion.
Select 3 answer choices that express the most important ideas in the passage. This question is worth 2 points.
Paragraph 1
The prevailing scientific model for the formation of our solar system and other planetary systems is the nebular hypothesis. This theory posits that a solar system begins as a vast, rotating cloud of interstellar gas and dust, known as a solar nebula. Under the influence of its own gravity, this cloud begins to collapse. As it contracts, the law of conservation of angular momentum dictates that its rotation must speed up, much like an ice skater pulling in their arms. This accelerated rotation causes the cloud to flatten into a spinning protoplanetary disk. The vast majority of the mass, primarily hydrogen and helium, collapses into the center, becoming increasingly hot and dense. Eventually, the temperature and pressure at the core become so extreme that nuclear fusion ignites, and a new star—a protostar—is born.
Paragraph 2
While the protostar forms at the center, the rest of the material in the protoplanetary disk is not idle. This disk is a cosmic nursery where planets are built through a process called accretion. Initially, tiny dust grains, composed of rock, ice, and metal, collide and stick together due to electrostatic forces. Over millions of years, these small clumps grow into pebble-sized objects, then boulder-sized planetesimals. As these planetesimals grow larger, their gravitational pull increases, allowing them to attract more material and smaller planetesimals at an ever-increasing rate. This runaway growth leads to the formation of protoplanets, bodies that can be as large as Mars or the Moon. The accretion process is not gentle; it is characterized by countless violent collisions.
Paragraph 3
The composition of the planets that form is largely determined by their distance from the central protostar. The region near the star is extremely hot, so only materials with high melting points, such as metals (iron, nickel) and silicates (rock), can condense into solid form. This explains the formation of the small, dense, terrestrial planets—Mercury, Venus, Earth, and Mars—in the inner solar system. Beyond a certain point, known as the frost line or snow line, temperatures are cold enough for volatile compounds like water, ammonia, and methane to freeze into solid ice grains. This is the realm of the gas giants and ice giants. Because ice is far more abundant in the protoplanetary disk than rock and metal, the protoplanets that formed beyond the frost line could grow much larger, much more quickly.
Paragraph 4
The massive cores of the outer protoplanets, rich in ice, exerted a powerful gravitational pull. This allowed them to capture vast amounts of the most abundant elements in the nebula—hydrogen and helium gas—before the solar wind from the young star blew the remaining gas out of the system. This rapid accumulation of gas created the enormous, low-density planets we know as Jupiter and Saturn. The more distant ice giants, Uranus and Neptune, were less successful in this gas-capture phase, likely because the nebula was less dense at their greater distance and they formed more slowly. Consequently, they are composed primarily of the original ice and rock from their cores with much thinner hydrogen and helium atmospheres. The entire process of clearing the disk, from the initial collapse to the final formation of stable planets, is thought to take a few hundred million years.
Paragraph 5
The final stage of planet formation is a period of dynamic instability and cleanup. The gravitational influence of the newly formed giant planets can send remaining planetesimals and protoplanets scattering throughout the solar system. Some are ejected into interstellar space, while others are sent careening into the inner solar system, leading to a period known as the Late Heavy Bombardment. This era of intense impacts is what created many of the craters we see on the Moon and other terrestrial bodies today. The asteroid belt, located between Mars and Jupiter, is thought to be the remnant of a protoplanet that was prevented from fully forming by the immense gravitational perturbations of Jupiter. Over time, the orbits stabilize, and the solar system settles into the relatively orderly configuration we observe today.
The word 'prevailing' in paragraph 1 is closest in meaning to...
The word 'perturbations' in paragraph 5 is closest in meaning to...
According to paragraph 1, why does a collapsing solar nebula spin faster?
What is the significance of the 'frost line' as described in paragraph 3?
What can be inferred from paragraph 4 about Jupiter compared to Neptune?
In paragraph 1, why does the author mention 'an ice skater pulling in their arms'?
What does the author imply about the asteroid belt in paragraph 5?
According to the passage, the terrestrial planets are composed mainly of rock and metal because...
Look at the four squares [■] that indicate where the following sentence could be added to paragraph 3. Where would the sentence best fit?
This temperature gradient created a fundamental division in the types of materials available for planet building.
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.
According to the nebular hypothesis, planetary systems form from the collapse of a gas and dust cloud, with planets being built through a process of accretion.
Select 3 answer choices that express the most important ideas in the passage. This question is worth 2 points.