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10. Our Barren Moon. Lunar plains & craters Manned lunar exploration The lunar interior The Moon ’ s geologic history The formation of the Moon. Moon Data (Table 10-1). Moon Data: Numbers. Diameter : 3,476 . km 0.27 . Earth Mass : 7.4 . 10 22 kg 0.012 . Earth

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10 our barren moon
10. Our Barren Moon
  • Lunar plains & craters
  • Manned lunar exploration
  • The lunar interior
  • The Moon’s geologic history
  • The formation of the Moon
moon data numbers
Moon Data: Numbers
  • Diameter: 3,476.km 0.27 . Earth
  • Mass: 7.4 . 1022 kg 0.012 . Earth
  • Density: 3.3 . water 0.61 . Earth
  • Orbit: 3.8 . 105 km 0.0026 . Earth
  • Day: 27.32 days 27.32 . Earth
moon data special features 1
Moon Data: Special Features – 1
  • The Moon is the Earth’s only natural satellite
  • The Moon is 1 of 7 large Solar System satellites
  • The Moon has essentially no atmosphere
  • The Moon’s near side has 2 different surfaces
    • The lunar highlands are very heavily cratered
    • The lunar lowlands have 14 maria (i.e., “seas”)
  • The Moon’s “far side” has only 1 mare
moon data special features 2
Moon Data: Special Features – 2
  • The Moon’s interior has a very small iron core
  • The Moon’s differential gravity causes tides
    • Gravity differences on opposite sides of the Earth
  • The Moon is intimately involved with eclipses
    • Solar eclipses: the Moon is in the middle
    • Lunar eclipses: the Earth is in the middle
the moon as seen from earth
The Moon As Seen From Earth
  • Synchronous axial rotation
    • 1-to-1 spin-orbit coupling
      • 1 spin on its axis for every 1 orbit around its parent object
    • The Moon points only one “face” toward Earth
      • The Moon seems to wobble left & right
        • Caused by changing orbital speed along an elliptical orbit
      • The Moon seems to nod up & down
        • Caused by the 5.15° tilt of the Moon’s rotational axis
  • Surface visibility
    • Bright & dark areas
      • Cratered bright lunar highlands
      • Smooth dark lunar maria
the moon s two hemispheres
The Moon’s Two Hemispheres
  • The “near” side
    • Very diverse
      • Lunar maria 14 “seas”
      • Lunar terrae (highlands) “lands”
        • Extensively cratered
  • The “far” side
    • Very homogeneous
      • Lunar maria 1 “sea”
      • Lunar terrae (highlands) “lands”
        • Extensively cratered
mare orientale
Mare Orientale
  • Most prominent feature on the Moon’s far side
    • Is not a mare in the traditional sense
      • It is not flooded with dark basalt lava
        • Lunar “far side” crust was too thick to be penetrated
      • It is a multi-ringed basin
    • Is a mare in one sense
      • It is a very large impact basin
  • Probable cause
    • Impact by a large asteroid or comet
mare orientale high res image
Mare Orientale: High Res. Image

http://apod.nasa.gov/apod/image/1103/orientale_lro.jpg

old unmanned lunar missions
Old Unmanned Lunar Missions
  • Impacters
    • Ranger program 3 of 9 spacecraft
      • Precursors to unmanned lunar landings
      • Transmitted TV pictures until impact
  • Orbiters
    • Lunar Orbiter program 5 of 5 spacecraft
      • Precursors to manned lunar landings
      • Returned 1950 images of 99.5% of the lunar surface
    • Clementine mission
      • Mapped lunar surface in UV, visible & IR wavelengths
    • Lunar Prospector mission
      • Evidence of up to 6 billion tons of lunar ice
  • Landers
    • Surveyor program 5 of 7 spacecraft
      • Soft-landed at various locations on the lunar surface
crater alphonsus up close afar
Crater Alphonsus: Up Close & Afar

From Ranger 9 From Earth

manned lunar exploration
Manned Lunar Exploration
  • Orbiters
    • Earth orbit
    • Lunar transfer orbit
    • Lunar orbit
  • Landers
    • Apollo 11Mare Tranquilitatis
    • Apollo 12
    • Apollo 13 Barely averted disaster
    • Apollo 14
    • Apollo 15
    • Apollo 16
    • Apollo 17
the lunar surface
The Lunar Surface
  • Many craters visible from Earth telescopes
    • ~30,000 craters > 1.0 km in diameter
      • ~ 85% of the lunar near side is covered with craters
      • ~ 98% of the lunarfarside is covered with craters
    • Millions of craters actually exist on the lunar surface
  • Craters are typically circular
    • Angle of impact has very little significance
    • Central peaks are commoninlarge craters
    • Upthrown crater rims are common on large craters
  • Maria are larger than craters
    • Tension fissures & pressure ridges are common
    • Rest ~2.0 to 3.0 km below the average lunar surface
      • Comparable to Earth’s ocean crust
    • Flood basalts similar to Columbia River basalt flows
moon rocks
Moon Rocks
  • Lunar rock formation
    • All lunar rocks result from heating & cooling
      • Heat is derived from impact processes
    • Strong evidence of chemical differentiation
  • Lunar rock types
    • Igneous rocks Cooled from magma
      • Basalt Rich in iron & magnesium Maria       
      • Anorthosite Rich in quartz & feldspar Highlands
    • Impact breccia Cemented by magma
      • Only appreciable lunar mechanical weathering process
  • Lunar regolith “Blanket of stone”
    • Fragments of existing lunar rock ~2 to 20 m thick
    • Fragments of incoming meteorites
moon rock ages
Moon Rock Ages
  • Basic physical processes
    • Radiometric age dating
      • Radioactive starting isotope Parent isotope
      • Stable ending isotope Daughter isotope
      • Measure the decay rate of the parent isotope
      • Measure the parent to daughter isotope ratio
  • Basic results
    • Mare basalts
      • ~3.1 to 3.8 billion years old
    • Highland anorthosites
      • ~4.0 to 4.3 billion years old
    • Period of intense bombardment
      • ~3.8 to 4.6 billion years ago
typical lunar rocks
Typical Lunar Rocks

Vesicular mare basalt Highland anorthosite

Impact breccia

the lunar interior
The Lunar Interior
  • Chemical differentiation did occur
    • Lowdensity materials floated to the lunar surface
    • High density materialssankto the lunarcenter
  • The Moon does have a tiny iron-rich core
    • The Moon’s core is ~ 3% of thelunarmass
    • The Earth’s core is~33% of the Earth’s mass
lunar magnetism
Lunar Magnetism
  • The past
    • Ancient igneous rocks retain a weak magnetic field
      • Implies a partially molten core when surface solidified
  • The present
    • No appreciable magnetic field
      • Implies an almost completely solidified core
    • Moonquakes
      • Only ~ 3,000 per year
        • Earth has ~ 1.5 million earthquakes per year
      • Magnitude from ~ 0.5 to 1.5
        • Far weaker than on Earth
      • Originate ~ 600 to 800 km beneath the surface
        • Far deeper than on Earth
      • Triggered by tides produced by Earth’s differential gravity
        • Vary by a factor of 2 due to the highly elliptical lunar orbit
earth moon dynamics
Earth–Moon Dynamics
  • Some evidence
    • Reflectors put on lunar surface by Apollo astronauts
    • Extremely precise distance measurements
      • Moon is moving away from Earth ~3.8 cm . yr–1
  • Basic physical processes
    • Differential lunar gravity raises ocean tides
    • Earth’s axial rotation drags tidal bulge ahead ~10°
      • This is caused by friction along ocean bottoms
      • This in turn causes two things
        • Earth’s tidal bulge pulls the Moon into a higher orbit
        • Earth’s tidal friction slows Earth’s rotation ~0.000 02 sec . yr–1
  • Some implications
    • The month will become progressively longer
    • The dream of really long days will at last be realized
    • One face of Earth will always face the Moon
the formation of earth s moon
The Formation of Earth’s Moon
  • Fission hypothesis Doubtful
    • Earth’s axial rotation was extremely fast
  • Capture hypothesis Doubtful
    • Earth’s gravity captured a planetesimal
  • Co-creation hypothesis Doubtful
    • Particles in Earth orbit accreted into the Moon
  • Collisional ejection hypothesis Probable
    • Earth was obliquely impacted by a planetesimal
      • Only 1.23% of the combined masses became the Moon
      • Absence of lunar volatiles supports this hypothesis
        • Intense heating was an inevitable part of the impact
      • Low average lunar density supports this hypothesis
        • Very little of Earth’s iron core was ejected
important concepts
Moon data

~27 % Earth’s diameter

~0.23% Earth’s mass

~60 % Earth’s density

The Moon as seen from Earth

Radically different near & far sides

Synchronous rotation (1-to-1 S.O.C.)

Cratered highlands & craterless maria

Lunar exploration

Unmanned

Impacters, orbiters & landers

Manned

Orbiters & landers

The lunar surface

Crater & maria visibility

Lunar rocks

Basalt & anorthosite

Impact breccia

The lunar interior

Chemical differentiation

Asymmetrical lunar crust

Mantle-dominated

Minimal iron core

Lunar magnetism

Weak ancient magnetic field

No appreciable present mag. Field

Earth-long-term Moon tidal dynamics

Lengthening days & months

Increasing Earth–Moon distance

Formation of Earth’s Moon

Fission hypothesis

Capture hypothesis

Co-creation hypothesis

Collisional ejection hypothesis

Important Concepts