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lecture08 - Astronomy 3 The Nature of the Universe...

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Astronomy 3: The Nature of the Universe Professor Alice Shapley Lecture 8: Terrestrial Planets (NGC 1499 Image credit: Markus Noller, Deep Sky Images)
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Logistics Quiz #4: due Monday, May 2nd, 10 pm. Available today after class at CCLE website Lab this week on:
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Review from Last Time The scale of solar system. Quick tour of the major solar system components. Clues to the formation of the solar system: organized orbits/ rotation of planets; terrestrial vs. jovian planets; the nature and locations of asteroids and comets; interesting exceptions to the patterns (motion of Venus and Uranus, the large size of Earth’s moon). A model for the formation of the solar system. The timescale of the formation of the solar system.
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The planets are tiny compared to the distances between them (a million times smaller than shown here). Two groups: the inner 4 Terrestrial Planets and the Outer 4 Jovian Planets and Pluto.
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Planetary Data
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The Sun, planets, and large moons orbit and rotate in an organized way. counterclockwise (seen from above the north pole)
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Terrestrial planets are small, rocky, and close to the Sun. Jovian planets are large, gas-rich, and far from the Sun. ( What about Pluto? We will come back to Pluto. )
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Thousands of rocky asteroids lie between Mars & Jupiter. Thousands of icy comets in vicinity of Neptune and beyond. Asteroids and comets far outnumber the planets and their moons.
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A successful theory of solar system formation must allow for exceptions to general rules , such as …
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Let us apply the principles we have learned. As gravity forced the cloud to become smaller, its almost imperceptible rotation increased and it began to spin faster and faster, like the ice skater. Conservation of angular momentum. Gravity always tries to make a cloud contract; particles on outside only feel forces from the inside. Higher density increases gravity.
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As the cloud contracts it begins to heat up in the center; compression of a gas increases its temperature. Collisions between particles tend to flatten the cloud into a disk shape. The orderly motions of our solar system today are a direct result of the solar system’s birth in a spinning, flattened cloud of gas. Computer simulations show this effect.
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Fig 9.5 Temperature was highest near the young Sun; too hot for hydrogen gas and compounds to condense.
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Earth’s Moon Where does our Moon come from? Earth’s moon was probably created when a big planetesimal slammed into the newly forming Earth (almost 4.5 billion years ago). Material from outer layer blasted into orbit around Earth (ring) and accreted into the Moon. Consistent with: Moon’s lower density, small core, similar oxygen isotope composition to Earth, relative lack of easily vaporized constituents. Other large impacts may be responsible for other exceptions like rotation of Venus and Uranus.
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Age dating of meteorites that are unchanged since they condensed and accreted tell us that the solar system is about 4.6 billion years old.
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