Chapter 8 Learning Goals PDF

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Learning Goals of Chapter 8 from AST-A100...

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Chapter 8 8.1 The search for origins  How did we arrive at a theory of solar system formation? o A successful theory must explain four major features of our solar system:  Patterns of motion, the existence of two types of planets  Terrestrial  Jovian  The presence of asteroids and comets  Exceptions to the rules o Developed over a period of more than two centuries, the nebular theory explains all four features and also can account for other planetary systems.  Where did the solar system come from? o The nebular theory holds that the solar system formed from the gravitational collapse of an interstellar cloud known as the solar nebula. o The cloud was the product of recycling of gas through many generations of stars within our galaxy. o This material consisted of 98% hydrogen and helium and 2% all other elements combined. 8.2 Explaining the Major features of the solar system  What caused the orderly patterns of motion? o As the solar nebula collapsed under gravity, natural processes caused it to heat up, spin faster, and flatten out as it shrank. o The orderly motions we observe today all came from the orderly motion of this spinning disk.  Why are there two major types of planets? o The inner regions of the solar nebula were relatively hot, so only metal and rock could condense into tiny solid grains  These grains accreted into larger planetesimals that ultimately merged to make the terrestrial planets. o Beyond the frost line, cooler temperatures also allowed more abundant hydrogen compounds to condense into ice, building ice-rich planetesimals  Some of these grew large enough for their gravity to draw in hydrogen and helium gas, forming the Jovian planets  Where did asteroids and comets come from? o Asteroids are the rocky leftover planetesimals of the inner solar system, and comets are the ice-rich leftover planetesimals of the outer solar system. These objects sill occasionally collide with planets or moons, but the vast majority of impacts occurred during the heavy bombardment in the solar system's first few hundred million years.  How do we explain "exceptions to the rules? o Most of the exceptions probably arose from collisions or close encounters with leftover planetesimals. o Our Moon is most likely the result of a giant impact between a Mars-size planetesimal and the young Earth. 8.3 The Age of the Solar System  How do we measure the age of a rock?

Radiometric dating is based on carefully measuring the proportions of radioactive isotopes and their decay products within rocks. o The ratio of the isotopes changes with the time in a steady and predictable way that we characterize by an isotope's half-life. The time it takes for half the atoms in a collection to decay. How do we know the age of the solar system? o Radiometric dating of the oldest meteorites tells us that accretion began in the solar nebula about 4.56 billion years ago, with the planets forming by about 4.5 million years ago. o

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