Astronomy Textbook Notes

Astronomy Textbook Notes - Chapter 19 The Origin of the...

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Chapter 19: The Origin of the Solar System 19-1 | Theories of Earth’s Origin What theories account for the origin of the solar system? Rene Descartes proposed that the solar system formed from a contracting vortex of matter—an evolutionary theory. Buffon later suggested that a passing star pulled matter out of the Sun to form the planets—a catastrophic history. Laplace’s nebular hypothesis required a contracting nebula to leave behind rings that formed each planet, but it could not explain the low angular momentum of the sun Modern astronomy reveals that the matter in our solar system was formed in the big bang, and the atoms heavier than helium were cooked up in a few generations of stars. The sun and planets evidently formed from a cloud of gas in the interstellar medium The solar nebula hypothesis proposes that the planets formed in a disk of gas and dust around the protostar that became the sun. Observations show that these disks are common 19-2 | A Survey of the Solar System What properties must these theories explain? The solar system is disk shaped in the orbital revolution of the planets and their moons and in the rotation of the planets on their axes The planets are divided into two types. The inner four planets are terrestrial— small, rocky, dense Earthlike worlds. The next four outward are Jovian planets that are large and low density All four of the Jovian worlds have ring systems and large families of moons. The terrestrial planets have no rings and few moons Most of the asteroids, small, irregular rocky bodies, are located between the orbits of Mars and Jupiter Comets are icy bodies that fall into the inner solar system along long elliptical orbits. As the ices vaporize and release dust, the comet develops a tail that points approximately away from the sun Meteoroids that fall into Earth’s atmosphere are vaporized by friction and are visible as meteors. Larger and stronger meteoroids may survive to reach the ground, there they are called meteorites The Kuiper belt is composed of small, icy bodies that orbit the sun beyond the orbit of Neptune The age of an object can be found by radioactive dating. The oldest rocks from Earth, the moon, and Mars have ages approaching 4.6 billion years. The oldest objects in our solar system are the meteorites, which have ages of 4.56 billion years. This is taken to be the age of the solar system 19-3 | The Story of Planet Building
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How do planets form? Condensation in the solar nebula converted some of the gas into solid bits of matter, which accreted to form billions of planetesimals Planets begin growing by accreting solid material. But once a planet approaches about 15 Earth masses, it can begin growing by gravitational collapse as it pulls in gas from the solar nebula According to the condensation sequence, the inner part of the solar nebula was so hot that only metals and rocky minerals could form solid grains. The dense
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Astronomy Textbook Notes - Chapter 19 The Origin of the...

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