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The Lunar Interior

The Lunar Interior. A Presentation by Kyle Stephens October 2, 2008. Ingredients for Planetary Evolution. Basic Questions: Homogeneous or layered interior? Enough heat to cause volcanic activity? How far from the sun? How large is the planetary body?. Planetary Evolution: Key Facts.

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The Lunar Interior

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  1. The Lunar Interior A Presentation by Kyle Stephens October 2, 2008

  2. Ingredients for Planetary Evolution Basic Questions: • Homogeneous or layered interior? • Enough heat to cause volcanic activity? • How far from the sun? • How large is the planetary body?

  3. Planetary Evolution: Key Facts Main elements to planetary differentiation: • Segregation into layers of different composition • Usually a rapid process (geologically speaking) • Volcanism • A slower process 3. Cataclysmic Bombardment • Separates the crust into different layers through melting

  4. Planetary Evolution: Key Facts • Body starts as homogeneous interior • Due to heat, entire body melts • Layers of crust, mantle, and core begin to form, with more dense materials sinking to the core (Iron, etc.) • Volcanism begins to affect the composition of the different layers • Image applies to Earth • Volcanism causes planet-wide resurfacing

  5. Planetary Evolution: The Moon • Homogeneous Interior (4.5 billion years ago) • Separation into layers (4.45 billion years ago) • Possible formation of metallic core (4.4 billion years) • Volcanism (4.3-3.2 billion years ago) • Major impacts (4.0-3.9 billion years ago) • Major activity ceases (3.0 billion years ago) • Minor impacts continue to form craters

  6. The Moon’s Crust • Regolith covers the lunar crust • Thickness varies by location: • Lunar maria: 4-5 meters thick • Highlands: ~10 meters thick • Regolith is formed by overlapping ejecta blankets from meteor impacts • Regolith “grows” by 1.5 mm per million years

  7. The Moon’s Crust • Primary composition: Feldspar (rock-forming mineral that crystallizes from magma) • Thickness varies with location • Near side (~55 km) • Far side (~100 km) • Due to varying crust thickness, the moon’s center of mass is offset

  8. The Moon’s Crust The Moon’s crust represents about 9% of the total mass.

  9. The Moon’s Crust: Lunar Maria • About 2.5 to 3 billion years ago, basaltic lava covered 17% of the moon’s surface • This lava filled the giant impact basins to form what is known today as the lunar maria • Lunar maria is only a few kilometers thick • Mascons: Large concentrations of lunar maria that cause a stronger gravitational attraction • Common in younger basins

  10. The Moon’s Crust • The moon is a “one plate planet” • No tectonic plates like Earth • Moon cooled rapidly • Heat is lost by conduction

  11. The Moon’s Mantle • The complete structure of the mantle is not known • Most data comes from the Apollo missions’ seismometers • “Moonquakes” reveal important information about the composition of the interior • Quakes usually originate from tidal effects or meteor impacts

  12. The Moon’s Mantle • “Moonquakes” are usually • over ten minutes in length • Most quakes originate deep • within the mantle • Figure (a) shows how the • seismic wave velocities are • used to identify certain • elements of the interior

  13. The Moon’s Mantle • Over three billion years ago, the mantle was filled with melted basaltic rock • Basaltic lava would flood the basins on the surface • Through conduction, the interior’s heat was lost • Today, the mantle is a lithosphere (unmelted)

  14. The Moon’s Mantle The graph to the left displays the fact that today, the moon’s internal temperature is too low to be molten.

  15. The Moon’s Mantle Two possible models of the lunar interior:

  16. The Moon’s (Possible) Core • If the moon does have a core, it would have formed very early on (4.4 billion years ago) • Upper limit for the core: 400-500 km radius • Would consist of about 4% of the moon’s volume • Current data supports, but does not prove that the moon has a core • Better seismic data is needed

  17. Questions? Sources: Planetary Interiors, Surfaces and Interiors of Terrestrial Planets, Encyclopedia of the Solar System, NASA.gov, Wikipedia

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