The Moon's composition and structure have been unveiled through Apollo missions and remote sensing. These explorations reveal a world of anorthosite crust, seismic activity, and a small molten core. The Moon's unique properties, from its mass to its synchronous rotation, shape its distinct character.

Lunar surface features tell a tale of cosmic impacts, ancient volcanism, and tectonic shifts. Unlike Earth's dynamic landscape, the Moon's terrain remains largely unchanged, preserving a record of its violent past. This stark contrast highlights the Moon's role as a cosmic time capsule.

The Moon's Composition, Structure, and Physical Properties

Lunar exploration's scientific impact

• Apollo missions and lunar sample returns provide direct evidence of Moon's composition and structure
  • Analysis of returned lunar rocks and soil reveal Moon's crust primarily composed of anorthosite, an igneous rock rich in calcium and aluminum
  • Seismic experiments conducted by astronauts during Apollo missions provide insights into Moon's interior structure
    • Moon has a crust, mantle, and a small, partially molten core
    • Lunar crust thicker on the far side compared to the near side
• Remote sensing data from lunar orbiters further enhance understanding of Moon's surface composition and mineralogy
  • Spectral data identify presence of various minerals, such as pyroxene, olivine, and ilmenite, in addition to anorthosite

Key properties of the Moon

• Moon has a mass of 7.34 x 10^22 kg, approximately 1.2% of Earth's mass
• Moon's gravity about 1/6th that of Earth's, with a surface gravitational acceleration of 1.62 m/s^2
  • Lower gravity on Moon due to its smaller mass compared to Earth
  • Reduced gravity affects behavior of objects and materials on lunar surface (motion of astronauts, shape of impact craters)
• Moon lacks a significant atmosphere
  • Lunar atmosphere considered an exosphere, with extremely low density and pressure
  • Lack of substantial atmosphere attributed to Moon's low gravity and inability to retain atmospheric gases
  • Absence of atmosphere results in lack of weather phenomena (wind, precipitation) on lunar surface
• Moon exhibits synchronous rotation, always showing the same face to Earth

Moon vs Earth surface features

• Moon's surface characterized by impact craters, volcanic features, and tectonic structures, while Earth's surface dominated by plate tectonics, erosion, and weathering
  • Impact craters more prevalent and better preserved on Moon due to lack of atmospheric protection and weathering processes
    • Moon's craters range in size from micrometers to hundreds of kilometers in diameter
  • Volcanic features on Moon include mare basalts, sinuous rilles, and domes
    • Mare basalts are vast, dark plains of solidified lava that fill many of Moon's impact basins (lunar maria)
    • Sinuous rilles are channel-like features thought to be formed by ancient lava flows
    • Domes are small, rounded hills that may represent volcanic constructs
  • Tectonic structures on Moon primarily a result of its thermal history and include wrinkle ridges and graben
    • Wrinkle ridges are linear, raised features that form due to compressional stresses in lunar crust
    • Graben are linear depressions bounded by parallel normal faults, indicating extensional stress
• Moon lacks active plate tectonics, hydrological cycle, and atmospheric processes that shape Earth's surface
  • Absence of these processes results in relatively static and ancient lunar surface compared to Earth's dynamic and continually evolving surface
• Space weathering, caused by micrometeorite impacts and solar wind bombardment, is primary weathering process on Moon
  • Space weathering alters optical properties and chemical composition of lunar regolith over time, darkening and reddening its appearance

Lunar Surface Features

• Highlands: Light-colored, heavily cratered regions of the Moon's surface, primarily composed of anorthosite
• Mascons: Concentrations of mass beneath the lunar surface, often associated with impact basins and affecting the Moon's gravitational field