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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

The Lunar Interior

A Presentation by Kyle Stephens

October 2, 2008

ingredients for planetary evolution
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
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
planetary evolution key facts4
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
planetary evolution the moon
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
the moon s crust
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
the moon s crust7
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

the moon s crust8
The Moon’s Crust

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

the moon s crust lunar maria
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
the moon s crust10
The Moon’s Crust
  • The moon is a “one plate planet”
  • No tectonic plates like Earth
    • Moon cooled rapidly
  • Heat is lost by conduction
the moon s mantle
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
the moon s mantle12
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
the moon s mantle13
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)
the moon s mantle14
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.

the moon s mantle15
The Moon’s Mantle

Two possible models of the lunar interior:

the moon s possible core
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
questions
Questions?

Sources: Planetary Interiors, Surfaces and Interiors of Terrestrial Planets, Encyclopedia

of the Solar System, NASA.gov, Wikipedia