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: http://www.badastronomy.com/bad/tv/foxapollo.html •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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2 Astro 102/104 5 Some Hypotheses • Many theories have been proposed for the Moon's origin • Generally, they have fallen into three categories: Fission • The Moon was once part of the Earth but separated from it early in their history Co-accretion • The Moon formed together with (but independently of) the
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This note was uploaded on 03/04/2008 for the course ASTRO 1102 taught by Professor Squyres,s/margot,j during the Spring '07 term at Cornell University (Engineering School).

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

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