Moon Module 4

Module Four: Earth's Moon

Characteristics of the Moon

• Distance from Earth: 384,000 km

• Only celestial body visited by humans

• Lacks atmosphere

Comparison of Earth and Moon

• Mass:

  • Earth = 6.0 x 10^24 kg

  • Moon = 1 (relative)

• Radius:

  • Earth = 6400 km

  • Moon = 1 (relative)

• Average Density:

  • Earth = 5500 kg/m³

  • Moon = 1 (relative)

• Surface Gravity:

  • Earth = 11 km/s

  • Moon = 1 (relative)

• Escape Speed:

  • Earth = 1 (relative)

  • Moon = 1 (relative)

Moon's Interior

• Uniform density

• Chemically differentiated

• Weak moonquakes present

• No magnetosphere

• No plate tectonic movement

• Layers:

  • Mantle: partial melt

  • Outer core: fluid

  • Inner core: solid

  • Thickness:

    • Mantle = 240 km

    • Outer core = 330 km

    • Inner core = 480 km

The Surface of the Moon

Lowlands or Marias

• Large dark flat areas created by lava flows

• Composed mainly of basalt

• Term 'maria' means “seas” as early observers mistook these for oceans

Highlands

• Light-colored elevated areas

• Composed of lower density rocks called Anorthosite

The Far Side of the Moon

• The same side of the Moon always faces Earth due to tidal locking

• Remained unknown until Apollo missions

• Relatively unmarked by craters compared to the near side

Crater Formation on the Moon

• Created by meteoroid strikes, which eject material

• Crater dimensions: typically about 10 times the width of the impacting meteoroid and twice as deep

• Rock is pulverized to much greater depths

• Most lunar craters date to at least 3.9 billion years ago, with significantly less bombardment since then

Craters of the Moon

• Includes both large and small craters

• Notable crater: Copernicus

Regolith of the Moon

• Thick layer of dust resulting from meteorite impacts

• Acts as the “soil” on the Moon’s surface

• Continues to be bombarded by small "micrometeoroids"

• Lack of erosion or atmosphere allows astronaut footprints to remain

Formation of the Moon – Disproved Theories

• Coformation Theory: Proposed Earth and Moon formed simultaneously from the same material

• Capture Theory: Suggested that the Moon was independently formed and later captured by Earth's gravity

• Both theories are unsupported by composition evidence of Earth and Moon

Formation of the Moon – Impact Theory

• Currently accepted explanation

• A Mars-sized body collided with a still-liquid Earth, ejecting material primarily from the mantle to form the Moon

• Impact Theory accounts for the differing compositions of Earth and Moon

Sequence of Events in the Formation of the Moon

• 4 Billion Years Ago: Moon had many craters but no maria

• 3 Billion Years Ago: Formation of maria as lava flowed from cracks caused by impacts

• Crater impacts continued but lava ceased

• Surface remains unchanged due to lack of erosion and atmosphere.