Earth and the Moon

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Earth and the Moon

• Paul J. Thomas
• Department of Physics and Astronomy
• UW Eau Claire

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Structure of the Earth
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Plate Tectonics
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Plate Tectonics
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The Moon
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The Earth and Moon
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Luna 3

• Soviet spacecraft, launched October 1959.
• Returned first images of lunar far side.
• Images show farside to be very different from
  nearside.
• Very few maria
• Mostly highlands

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The Surface of the Moon

• Synchronous rotation
• Two distinct surfaces
• Highlands 83 of surface, primarily anorthosite,
  4.0-4.3 Gyr old
• Maria 17 of surface, primarily basalt, 3.1-3.8
  Gyr old
• Mass concentrations (mascons) beneath maria.
• Oldest lunar rock is 4.48 Gyr old

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Apollo Landings 1969-72
Between July 1969 and December 1972, six
successful landings returned 382 kg of lunar
rocks, pebbles, dust and core samples.
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Lunar Prospector Discovers Ice at the Lunar Poles

• Launched January 7, 1998.
• Intentionally crashed on Moons South Pole July
  31, 1999.
• Neutron spectrometer experiment detected ice at
  both North and South Poles.

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Ice at the Lunar Poles

• How much ice?
• 11-330 million tons, twice as much at North Pole
  than at South Pole.
• Consistent with the presence of water ice in
  very low concentrations across a significant
  number of craters.
• 0.3-1.0 mixing ratio with lunar regolith.

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Importance of Ice at the Lunar Poles

• Science
• Helps us to understand comet impact history (did
  comets deliver the water in the Earths oceans?)
  study comet compositions.
• Spaceflight
• This could be a resource for future lunar bases.

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The Moon Origin

• A successful theory for the origin of the Moon
  must explain
• relatively large Moon mass/Earth mass ratio
• Moon was formed early in solar system history
• Moon was closer to Earth in past
• Moon similar to Earth (oxygen isotope ratios)
• Moon dissimilar to Earth (no iron core no
  volatiles)

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The Moon Giant Impact Model

• Mars-sized impactor hit Earth a glancing blow
  during final stages of Heavy Bombardment,
  throwing hot material off to form the Moon
• Advantages
• Material comes from Earth (similar composition of
  metals) but is heated (driving off volatiles)
• Iron core is left behind in Earth

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Giant Impact Theory of Lunar Formation