Planetary Geology

Layering of Terrestrial Worlds

• The process of differentiation separates materials with different densities

• Dense metals fall to the central core• Rocky material (minerals) form the mantle resting

above the core• The lowest density materials form the outer layers

called the crust• The crust and the outermost layers of the mantle

form a rigid lithosphere (lower layers are softer)

Example of a Terrestrial World

Terrestrial Planets and the Moon

• The interiors are hotter and denser

• Note trends with size and distance from Sun

Three Sources of Internal Heating

• Accretion of planetesimals continues after formation and can change the composition slightly

• Differentiation occurs because the materials are hot and molten

• Nuclear reactions occur in the dense central regions

Planetary Cooling

• Conduction directly transfers heat from the lower layers to the upper layers

• Convection carries warmer parts of the mantle closer to crust

• Eruptions deposit hot lava onto the surface where it cools

Planetary Magnetic Fields

• Requirements for a planetary magnetic field:– Metal in liquid or

molten form needed

– Convection in these liquid layers

– Moderately rapid rotation

Formation Properties and Controlling Factors

Geological Processes

• Impact cratering: asteroids, comets, and other planetesimals impacting the surface

• Volcanism: the eruption of molten rock (lava) onto the surface

• Tectonics: the disruption of the surface due to internal forces (e.g. convection in mantle)

• Erosion: the wearing down of surface features by water, wind, and other factors

Impact Cratering

The Moon Crater Tycho

Cratering on the Moon

Cratering Rate

Martian Crater

Volcanism

Volcanic Activity

The Near Side of the Moon

Tectonics on Earth and Venus

Past Tectonics on Mercury

One Type of Erosion: Wind