Transcript The Lunar Interior

The Lunar Interior
A Presentation by Kyle Stephens
October 2, 2008
Ingredients for Planetary Evolution
Basic Questions:
1.
2.
3.
4.
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
Main elements to planetary differentiation:
1. Segregation into layers of different composition
 Usually a rapid process (geologically speaking)
2. Volcanism
 A slower process
3. Cataclysmic Bombardment
 Separates the crust into different layers through
melting
Planetary Evolution: Key Facts
a) Body starts as homogeneous
interior
b) Due to heat, entire body melts
c) Layers of crust, mantle, and core
begin to form, with more dense
materials sinking to the core (Iron,
etc.)
d) Volcanism begins to affect the
composition of the different layers
e) Image applies to Earth
f) Volcanism causes planet-wide
resurfacing
Planetary Evolution: The Moon
1. Homogeneous Interior (4.5 billion years ago)
2. Separation into layers (4.45 billion years ago)
3. Possible formation of metallic core (4.4 billion years)
4. Volcanism (4.3-3.2 billion years ago)
5. Major impacts (4.0-3.9 billion years ago)
6. Major activity ceases (3.0 billion years ago)
7. Minor impacts continue to form craters
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 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 Crust
The Moon’s crust represents about 9% of the total mass.
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 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 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 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 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 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 Mantle
Two possible models of the lunar interior:
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?
Sources: Planetary Interiors, Surfaces and
Interiors of Terrestrial Planets, Encyclopedia
of the Solar System, NASA.gov, Wikipedia