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Astronomy Chp. 12

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1) Which of the following statements about comets and asteroids is true?
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Comets are balls of ice and dust.
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2) What do asteroids and comets have in common?
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Most are unchanged since their formation in the solar nebula.
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3) A rocky leftover planetesimal orbiting the Sun is
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an asteroid.
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4) An icy leftover planetesimal orbiting the Sun is
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a comet.
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5) Why do asteroids and comets differ in composition?
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Asteroids formed inside the frost line, while comets formed outside.
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6) What is the size of the largest asteroid?
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1,000 km
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7) How does the largest asteroid, Ceres, compare in size to other solar system worlds?
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It is about a quarter the size of the Moon.
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8) Which is closest to the average distance between asteroids in the asteroid belt?
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1 million km
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9) The combined mass of all the asteroids in the asteroid belt is
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less than that of any terrestrial planet.
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10) Where are the Trojan asteroids located?
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along Jupiter’s orbit, 60° ahead of and behind Jupiter
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11) We know that there are large gaps in the average distances of asteroids from the Sun (within the asteroid belt) because we
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have plotted distributions of the orbital radii of the asteroids.
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12) The large gaps in the asteroid belt (often called Kirkwood gaps) are caused by
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orbital resonances with Jupiter.
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13) Why do we sometimes observe asteroids at the distances of the gaps in the asteroid belt?
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A gap is located at an average orbital distance, and asteroid orbits often have large eccentricities.
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14) Why isn’t there a planet where the asteroid belt is located?
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Gravitational tugs from Jupiter prevented material from collecting together to form a planet.
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15) How can we determine an asteroid’s reflectivity?
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by comparing its infrared thermal emission to its visible-light reflection
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16) If we know the size of an asteroid, we can determine its density by
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determining its mass from its gravitational pull on a spacecraft, satellite, or planet.
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17) Why aren’t small asteroids spherical in shape?
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The strength of gravity on small asteroids is less than the strength of the rock.
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18) What is a meteorite?
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a fragment of an asteroid from the solar system that has fallen to Earth’s surface
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19) What do we call a small piece of solar system debris found on Earth?
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meteorite
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20) A typical shooting star in a meteor shower is caused by a ________ entering Earth’s atmosphere.
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pea-size particle from a comet
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21) What characteristic distinguishes a meteorite from a terrestrial rock? A) A meteorite is usually covered with a dark crust from burning in Earth’s atmosphere. B) A meteorite usually has a high metal content. C) Meteorites have different isotope ratios of particular elements when compared to terrestrial rocks. D) Meteorites contain rare elements, such as iridium, that terrestrial rocks do not.
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all
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22) Primitive meteorites can be distinguished from other meteorites and terrestrial rocks because they
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contain a noticeable fraction of pure metallic flakes.
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23) Most meteorites are
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rocky and primitive.
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24) Processed meteorites with low metal content probably are
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chunks of a larger asteroid that was shattered by a collision.
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25) Meteorites can come from
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the cores of asteroids, the Moon, Mars, and comets.
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26) Halley’s comet is named after the English scientist Edmund Halley because he
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calculated its orbit and predicted that it would return in 1758.
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27) In order to have a comet named after you, you have to
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be one of the first three discoverers who report it to the International Astronomical Union (IAU).
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28) When do comets generally begin to form a tail?
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inside of Jupiter’s orbit
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29) What part of a comet points most directly away from the Sun?
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the plasma tail
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30) Why does the plasma tail of a comet always point away from the Sun?
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The solar wind electromagnetically “blows” the ions directly away from the Sun.
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31) Where did comets that are now in the Oort cloud originally form?
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near the jovian planets
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32) Where did comets that are now in the Kuiper belt originally form?
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near the radius at which they orbit today
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33) Comets with extremely elliptical orbits, like comets Hyakutake and Hale-Bopp,
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come from the Oort cloud.
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34) The number of comets in the Oort cloud is probably about
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a trillion.
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35) What is the typical size of comets that enter the inner solar system?
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10 km
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36) When was Pluto discovered?
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about 80 years ago
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37) Why won’t Pluto collide with Neptune?
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The two planets have an orbital resonance that prevents them from colliding.
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38) What is Charon?
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Pluto’s moon
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39) Which of the following does not lend support to the idea that Pluto is a Kuiper-belt object? A) Pluto has a comet like composition and density. B) Pluto is regarded by many to be a planet. C) Some asteroids have their own moons. D) Pluto has a more eccentric orbit than other planets. E) Some known Kuiper-belt objects are hundreds of kilometers across.
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Pluto is regarded by many to be a planet
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40) In the asteroid impact theory of the extinction of the dinosaurs some 65 million years ago, the dinosaurs (and over half of all the other species on Earth at that time) died off largely because
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dust injected into the stratosphere from the impact absorbed visible light from the Sun, causing global temperatures to plummet.
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41) Why was the Shoemaker-Levy 9 impact so important to astronomers?
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It dredged up material that gave us our first direct look at Jupiter’s interior composition.
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42) On average, how often do impactors about 10 km in size, large enough to produce mass extinction, hit Earth?
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once every hundred million years
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43) Which of the following Pluto observations did not help convince scientists to change Pluto’s status from that of a planet? A) discovery of the Kuiper Belt B) discovery of seasonal atmosphere, similar to comets C) discovery of large Kuiper Belt Objects D) discovery of Pluto’s 3 moons
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discovery of Pluto’s 3 moons
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12.2 True/False Questions
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1) T or F A spacecraft traveling through the asteroid belt has a high risk of being destroyed through a collision.
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FALSE
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2) T or F Falling stars and shooting stars are simply other names for meteors.
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TRUE
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3) T or F Most meteorites collected on Earth are of the rocky primitive variety, although most asteroids are of the carbon-rich variety.
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TRUE
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4) T or F All meteorites collected on Earth come from asteroids or comets.
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FALSE
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5) T or F No spacecraft has ever visited an asteroid or comet.
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FALSE
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6) T or F Comet nuclei can be darker than charcoal.
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TRUE
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7) T or F Oort-cloud comets are so far from the Sun that the gravity of neighboring stars can alter their orbits.
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TRUE
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8) T or F The total mass of the Kuiper belt is greater than that of the asteroid belt.
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TRUE
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9) T or F Pluto’s gravity affects the orbit of Uranus, and this fact was used to discover Pluto.
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FALSE
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10) T or F Viewed from Pluto, the Sun would appear more than a thousand times fainter than on Earth.
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TRUE
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11) T or F A comet that has an orbit around the Sun inclined to the ecliptic plane by 65° probably originated in the Kuiper belt.
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FALSE
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12) T or F Process of Science: Observations of asteroids, comets, and meteorites help refine the theory of the formation of the solar system.
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TRUE
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12.4 Mastering Astronomy Reading Quiz
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1) Which of the following statements is not true? A) Objects in the asteroid belt are made mostly of rock and metal. B) Objects in the Kuiper belt are made mostly of rock and metal. C) Objects in the Oort cloud contain large proportions of ice. D) Objects in the asteroid belt and Kuiper belt orbit the Sun in nearly the same plane as the planets, but objects in the Oort cloud do not.
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Objects in the Kuiper belt are made mostly of rock and metal
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2) A rock found on Earth that crashed down from space is called
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a meteorite.
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3) The asteroid belt is located
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between the orbits of Mars and Jupiter.
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4) Which statement about asteroids is not true? A) Many but not all orbit the Sun in the asteroid belt. B) Some are more like loosely bound piles of rubble than solid chunks of rock. C) Most asteroids are not spherical in shape. D) If we could put all the asteroids together, they would make an object about the size of Earth.
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If we could put all the asteroids together, they would make an object about the size of Earth.
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5) A typical meteor is created by a particle about the size of a
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pea.
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6) What do we mean by a primitive meteorite?
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a meteorite that is essentially unchanged since it first condensed and accreted in the solar nebula some 4.6 billion years ago
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7) Among discovered meteorites, we have found some with all the following origins except
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being a fragment from Comet Halley.
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8) Which statement is not thought to be true of all comets in our solar system? A) Comets always have tails. B) All comets are icy in composition. C) All comets orbit the Sun. D) All comets are leftover planetesimals that originally condensed beyond the frost line in the solar nebula.
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Comets always have tails
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9) Which direction do a comet’s dust and plasma tails point?
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generally away from the Sun
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10) When a comet passes near the Sun, part of it takes on the appearance of a large, bright ball from which the tail extends. This part is called
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the coma.
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11) The total number of comets orbiting the Sun is estimated to be about
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1 trillion.
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12) Halley’s comet is named after the English scientist Edmund Halley (1656-1742) because
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he calculated its orbit and predicted the year in which it would next be seen.
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13) What is Charon?
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the largest of Pluto’s three known moons
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14) According to current evidence, Pluto is best explained as
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a large member of the Kuiper belt.
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15) What is Eris?
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an icy object that orbits in the Kuiper belt and is larger than Pluto
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16) What was the Shoemaker-Levy 9 impact?
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the 1994 impact of a chain of comet fragments into Jupiter
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17) What do we mean by a mass extinction?
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the extinction of a large fraction of the world’s plant and animal species in a relatively short period of time
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18) If the hypothesis tracing the extinction of the dinosaurs to an impact is correct, the dinosaurs died off largely because
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of global climate effects initiated by dust and smoke that entered the atmosphere after the impact.
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12.5 Mastering Astronomy Concept Quiz
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1) Which of the following statements best describes the size of the largest asteroid, Ceres?
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It is a little less than half the diameter of our Moon.
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2) If we could put all the asteroids together, their total mass would be
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much less than the mass of any terrestrial planet.
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3) Why didn’t a planet form where the asteroid belt is now located?
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Gravitational tugs from Jupiter prevented material from collecting together to form a planet.
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4) Gaps in the asteroid belt (often called Kirkwood gaps) are caused by
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orbital resonances with Jupiter.
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5) When you see the bright flash of a meteor, what are you actually seeing?
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the glow from a pea-size particle and the surrounding air as the particle burns up in our atmosphere
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6) How can we determine the reflectivity of an asteroid?
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by comparing its brightness in visible light to its brightness in infrared light
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7) In science fiction movies, spaceships are often shown dodging through large numbers of closely spaced, boulder-size objects. Which of the following real things in our solar system would look most like such science fiction dangers?
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the rings of Saturn
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8) Suppose you find a meteorite made almost entirely of metal. According to current science, which of the following statements must be true?
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Your meteorite is a fragment from the core of a large asteroid that shattered in a collision.
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9) Which of the following objects are probably not located in the same region of the solar system in which they originally formed? A) Kuiper belt comets B) Oort cloud comets C) asteroids of the asteroid belt D) Pluto
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Oort cloud comets
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10) Suppose there were no solar wind. How would the appearance of a comet in our inner solar system be different?
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It would have only one tail instead of two.
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11) Suppose we discover a new comet on an orbit that brings it closer to the Sun than Mercury every 125 years. What can we conclude?
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It has been on its current orbit for only a very short time compared to the age of our solar system.
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12) When we see a meteor shower, it means that
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Earth is crossing the orbit of a comet.
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13) Why won’t Pluto collide with Neptune?
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Pluto orbits the Sun exactly 2 times for every 3 Neptune orbits, which ensures they never come close together.
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14) What is Pluto’s moon Charon thought to have in common with our own Moon?
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It probably formed as a result of a giant impact.
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15) Which of the following is not a piece of evidence supporting the idea that Pluto is a large comet of the Kuiper belt?A) Pluto’s composition appears to match that of other known Kuiper belt comets. B) Triton, which must once have orbited the Sun before being captured by Neptune, is significantly larger than Pluto. C) Pluto grows a coma and a long tail when it is at the point in its orbit closest to the Sun. D) Pluto’s orbit is very similar to the orbits of other known Kuiper belt comets. E) Pluto is not the largest object orbiting in the region of the Kuiper belt.
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Pluto grows a coma and a long tail when it is at the point in its orbit closest to the Sun
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16) The discovery of Eris
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was not surprising, because other Kuiper belt objects approaching the size of Pluto had already been discovered.
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17) Which of the following is not a piece of evidence supporting the idea that an impact caused the mass extinction that occurred 65 million years ago? A) Fossilized dinosaur bones contain fragments of rock from the impact. B) Unusually large abundances of iridium and other rare metals are found in a layer of clay that dates to 65 million years ago. C) A large impact crater along the coast of Mexico dates to 65 million years ago. D) Grains of quartz formed under high pressure are found in a layer of clay that dates to 65 million years ago.
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Fossilized dinosaur bones contain fragments of rock from the impact
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18) Suppose that large jovian planets had never formed in our solar system. Which of the following would most likely be true?
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Neither the asteroid belt nor Oort cloud would exist.