Lecture14 - Lecture#14 Origin of the Moon Observations...

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1 Astro 102/104 1 Lecture #14: Origin of the Moon • Observations Classical models for the formation of the Moon A relatively new idea: the Giant Impact theory • Reading: – Chapters 8.4, 9.3 Astro 102/104 2 Moon Hoax? • Apollo conspiracy theories retain a limited following • “Conspiracy Theory: Did We Land on the Moon?” (Fox TV, 2001) – NASA faked Moon landings in Nevada desert (Area 51) Î Thoroughly discredited at: • Do you think 400,000 people could keep a secret this long? Astro 102/104 3 The Main Point There are four main hypotheses for the origin of the Moon. The most widely accepted among astronomers today is the giant impact hypothesis. Astro 102/104 4 Observations Any successful theory for the origin of the Moon must account for everything we know about the Moon now. Facts: The Moon’s mantle composition is in some ways similar to Earth’s (oxygen isotopes), and in other ways different (volatile abundances) The Moon is much less dense than Earth (no large iron core) The Moon orbits in the same direction as the Earth rotates The Moon is slowly drifting away from the Earth The Moon was once much closer to the Earth
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