Astronomy Ch. 8 Practice Test – Flashcards
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Which of the following best explains why we can rule out the idea that planets are usually formed by near-collisions between stars?
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Stellar near-collisions are far too rare to explain all the planets now known to orbit nearby stars.
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According to our modern science, which of the following best explains why the vast majority of the mass of our solar system consists of hydrogen and helium gas?
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Hydrogen and helium are the most common elements throughout the universe, because they were the only elements present when the universe was young.
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According to our theory of solar system formation, which law best explains why the central regions of the solar nebula got hotter as the nebula shrank in size?
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The law of conservation of energy
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According to our theory of solar system formation, which law best explains why the solar nebula spun faster as it shrank in size?
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The law of conservation of angular momentum
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According to our present theory of solar system formation, which of the following best explains why the solar nebula ended up with a disk shape as it collapsed?
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It flattened as a natural consequence of collisions between particles in the nebula.
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What is the primary basis upon which we divide the ingredients of the solar nebula into four categories (hydrogen/helium; hydrogen compound; rock; metal)?
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The temperatures at which various materials will condense from gaseous form to solid form.
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According to our present theory of solar system formation, which of the following statements about the growth of terrestrial and jovian planets is not true?
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The jovian planets began from planetesimals made only of ice, while the terrestrial planets began from planetesimals made only of rock and metal.
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Many meteorites appear to have formed very early in the solar system's history. How do these meteorites support our theory about how the terrestrial planets formed?
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The meteorites appearance and composition is just what we'd expect if metal and rock condensed and accreted as our theory suggests.
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According to present understanding, which of the following statements about the solar wind is not true?
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It is even stronger today than it was when the Sun was young.
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According to our present theory of solar system formation, how did Earth end up with enough water to make oceans?
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The water was brought to the forming Earth by planetesimals that accreted beyond the orbit of Mars.
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What is the primary reason that astronomers suspect that some jovian moons were captured into their current orbits?
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Some moons have orbits that are "backwards" (compared to their planet's rotation) or highly inclined to their planet's equator.
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Which of the following is not a line of evidence supporting the hypothesis that our Moon formed as a result of a giant impact?
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The Pacific Ocean appears to be a large crater - probably the one made by the giant impact.
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Why are terrestrial planets denser than jovian planets?
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The terrestrial planets formed in the inner solar nebula, where only dense materials could condense.
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Suppose you find a rock that contains 10 micrograms of radioactive potassium-40, which has a half-life of 1.25 billion years. By measuring the amount of its decay product (argon-40) present in the rock, you conclude that there must have been 80 micrograms of potassium-40 when the rock solidified. How old is the rock?
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3.75 billion years
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How do scientists determine the age of the solar system?
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Radiometric dating of meteorites
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The region of our solar system between Mercury and Mars has very few asteroids, while the region between Mars and Jupiter has many asteroids. Based on what you have learned, what is the most likely explanation for the lack of asteroids between Mercury and Mars?
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There were very few planetary leftovers in this region, because most of the solid material was accreted by the terrestrial planets as the planets formed.
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About 2% of our solar nebula consisted of elements besides hydrogen and helium. However, the very first generation of star systems in the universe probably consisted only of hydrogen and helium. Which of the following statements is most likely to have been true about these first-generation star systems?
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There were no comets or asteroids in these first-generation star systems.
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In essence, the nebular theory holds that _________.
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our solar system formed from the collapse of an interstellar cloud of gas and dust
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According to modern science, what was the approximate chemical composition of the solar nebula?
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98% hydrogen and helium, 2% everything else
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The terrestrial planets are made almost entirely of elements heavier than hydrogen and helium. According to modern science, where did these elements come from?
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They were produced by stars that lived and died before our solar system was born.
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According to our theory of solar system formation, what three major changes occurred in the solar nebula as it shrank in size?
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It got hotter, its rate of rotation increased, and it flattened into a disk.
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Which of the following types of material can condense into what we call ice at low temperatures?
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hydrogen compounds
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According to our present theory of solar system formation, which of the following lists the major ingredients of the solar nebula in order from the most abundant to the least abundant?
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hydrogen and helium gas; hydrogen compounds; rock; metal.
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What do we mean by the frost line when we discuss the formation of planets in the solar nebula?
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It is a circle at a particular distance from the Sun, beyond which the temperature was low enough for ices to condense.
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What do we mean by accretion in the context of planet formation?
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The growth of planetesimals from smaller solid particles that collided and stuck together
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According to our present theory of solar system formation, why were solid planetesimals able to grow larger in the outer solar system than in the inner solar system?
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Because only metal and rock could condense in the inner solar system, while ice also condensed in the outer solar system.
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According to our basic scenario of solar system formation, why do the jovian planets have numerous large moons?
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As the growing jovian planets captured gas from the solar nebula, the gas formed swirling disks around them, and moons formed from condensation accretion within these disks.
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According to our theory of solar system formation, what are asteroids and comets?
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Leftover planetesimals that never accreted into planets
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According to our theory of solar system formation, where did the comets originally form?
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in the outer solar system beyond the frost line
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What do we mean by the period of heavy bombardment in the context of the history of our solar system?
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The first few hundred million years after the planets formed, which is when most impact craters were formed.
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What is the giant impact hypothesis for the origin of the Moon?
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The Moon formed from material blasted out of the Earth's mantle and crust by the impact of a Mars-size object.
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Suppose you start with 1 kilogram of a radioactive substance that has a half-life of 10 years. Which of the following statements will be true after 20 years pass?
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You'll have 0.25 kilogram of the radioactive substance remaining.
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According to modern scientific dating techniques, approximately how old is the solar system?
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4.5 billion years
