Astronomy Chapter 8 Test Questions – Flashcards
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What percentage of the mass of the solar nebula consisted of elements other than hydrogen and helium?
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2 percent
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Where did the elements heavier than hydrogen and helium come from?
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they were produced from inside stars
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Why did the solar nebula heat up as it collapsed?
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as the cloud shrank, its gravitational potential energy was converted to kinetic energy and then into thermal energy
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Why did the solar nebula flatten into a disk?
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it flattened as a natural consequence of collisions between particles in the spinning nebula, changing random motions into more orderly ones
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What happened during the accretion phase of the early solar system?
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particles grew by colliding and sticking together
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According to our theory of solar system formation, why do all the planets orbit the Sun in the same direction and in nearly the same place?
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the laws of conservation of energy and conservation of angular momentum ensure that any rotating, collapsing cloud will end up as a spinning disk
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Which of the following lists the ingredients of the solar nebula from highest to lowest percentage of mass of the nebula?
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light gases (H, He), hydrogen compounds (H2O, CH4, NH3), rocks, metals
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What percentage of the solar nebula's mass consisted of hydrogen and helium gases?
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98 percent
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What percentage of the solar nebula's mass consisted of rocky material?
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0.4 percent
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What kind of material in the solar nebula could remain solid at temperatures as high as 1,500K, such as existed in the inner regions of the nebula?
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metals
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What was the frost line of the solar system?
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the distance from the Sun where temperatures were low enough for hydrogen compounds to condense into ices, between the present-day orbits of Mars and Jupiter
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Why are the thinner planets made of denser materials than the outer planets?
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in the inner part of the nebula only metals and rocks were able to condense because of the high temperatures, whereas hydrogen compounds, although more abundant, were only able to condense in the cooler outer regions
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Which of the following is the origin of almost all the large moons around the jovian planets?
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they were formed by condensation and accretion in a disk of gas around the planet
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What is the most likely reason that there are no giant planets beyond Neptune?
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by the time planetesimals grew to a large enough mass to hold onto an atmosphere, the solar nebula had been blown away
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Observations of young stars (as well as theory) tell us that when the Sun was young the solar wind
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was stronger than it is today
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Which of the following has not been detected around other stars in the Galaxy?
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terrestrial planets
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At first, the Sun's present-day rotation seems to contradict the prediction of the nebular theory because
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the theory predicts that the Sun should have been rotating fast when it formed, but the actual rotation is fairly slow
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According to our theory of solar system foundation, why does the Sun rotate slowly today?
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the Sun once rotated much faster, but it transferred angular momentum to charged particles caught in its magnetic field and then blew the particles away with its strong solar wind
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Which of the following are relatively unchanged fragments from the early period of planet building in the solar system?
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all of the above
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According to the nebular theory, what are asteroids and comets?
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they are leftover planetesimals that never accreted into planets
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According to the nebular theory, how did the Kuiper belt form?
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It is made of planetesimals that formed beyond Neptune's orbit and never accreted to form a planet
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According to our theory of solar system formation, why do we find exceptions to the general rules and patterns of the planets?
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most of the exceptions are the result of giant impacts
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Based on our current theory of Earth's formation, the water we drink comes from
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comets that impacted Earth
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The heavy bombardment phase of the solar system lasted
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several hundreds of millions of years
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which of the following is not evidence supporting the giant impact theory for the formation of the Moon?
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Scientists have found several meteorites that appear to be the remains of the object that caused the giant impact
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which of the following puzzles in the solar system cannot be explained by a giant impact event?
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the orbit of Triton in the opposite direction to Neptune's rotation
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The nebular theory of the formation of the solar system successfully predicts all but one of the following. Which one does the theory not predict?
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the equal number of terrestrial and jovian planets
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The age of our solar system is approximately
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4.6 billion years
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The age of the solar system can be established by radioactive dating of
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the oldest meteorites
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What do meteorites reveal about the solar system?
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they reveal that the age of the solar system is approximately 4.6 billion year
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Suppose you find a rock that contains some potassium-40 (half-life of 1.3 billion years). You measure the amount and determine that there are 5 grams of potassium-40 in the rock. By measuring the amount of its decay product (argon-40) present in the rock, you realize that there must have been 40 grams of potassium-40 when the rock solidified. How old is the rock?
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3.9 billion years
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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
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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 with 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 of the Oort cloud come from?
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in the region of the jovian planets
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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 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
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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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Only dense materials could condense in the inner solar nebula
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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 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.
