Astronomy Chapter 8

25 July 2022
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The age of our solar system is approximately
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4.6 billion years.
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Why did the solar nebula flatten into a disk? The force of gravity from the planets pulled the material downward into a flat 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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The age of the solar system can be established by radioactive dating of
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oldest meteorites
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What kind of material in the solar nebula could remain solid at temperatures as high as 1,500 K, such as existed in the inner regions of the nebula?
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Metal
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Where did the elements heavier than hydrogen and helium come from?
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They were produced inside stars.
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Planet Formation
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Terrestrial- Accreted from planetesimals of rock and metal, surface dramatically altered during the heavy bombardment Jovian- large moons formed in surrounding disk of material, formed in regions cold enough to freeze water, ejected planetesimals that are new Oort cloud comets, formed in region of solar system with lower orbital speeds.
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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 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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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 years.
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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 plane?
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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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Observations of young stars (as well as theory) tell us that when the Sun was young the solar wind was stronger than it is today. was weaker
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was stronger than it is today.
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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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According to our theory of solar system formation, why do we find some 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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Abundance highest to lowest
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hydrogen & helium, hydrogen compounds, rock, metals Temp: metals, rocks, hydrogen compounds, and hydrogen & helium Solar Nebula farthest to closes: Hydrogen compounds, rock, metals
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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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What percentage of the solar nebula's mass consisted of hydrogen and helium gases?
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98 percent
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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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Why are the inner 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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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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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 the nebular theory, how did the Kuiper belt form?
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It is made of planetesimals between the orbits of Mars and Jupiter that never formed into a planet. It is made of planetesimals that formed beyond Neptune's orbit and never accreted to form a planet.
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Why did the solar nebula heat up as it collapsed? Collisions among planetesimals generated friction and heat.
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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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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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Which of the following are relatively unchanged fragments from the early period of planet building in the solar system? asteroids Kuiper belt comets the moons of Mars Oort cloud comets
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All of the above
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Formation of the solar system
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large cloud of gas & dust, contraction of the solar nebula, condensation of particles, accretion of planetesimals, clearing of the solar nebula