Transcript Terrestrial Planets PowerPoint Slides

Terrestrial Planets
Earthlike Worlds of
Rocks and Metals
Earth: Model Planet
• Mass and radius give
mass/volume = bulk density,
about 5.5 times water
• Key to composition, internal
structure, verified by seismic
waves
• Metals bulk density about 8,
rocks about 3; earth about 5050 metals/rocks
Density Layers
• Core (metals)
• Mantle (dense rocks)
• Crust (less dense rocks)
• Partially or fully melted to
separate by density
(differentiation)
Internal Energy
• Heat now at surface about 0.1 watt
per square meter
• Internal energy stored from
formation (by accretion) plus
radioactive decay =>
larger in past
• Infrared from surface escapes to
space, lost forever
Energy Outflow
• Volcanism: Molten material,
gases rise to surface; adds to
crust and atmosphere
• Tectonics: Any motions of the
crust; plate tectonics involve
large-scale motions
Age of Earth
• Radioactive dating: Decay of
isotopes with long half-lives
• Gives elapsed time since rock
last melted and solidified
(remelting resets clock)
• Oldest rocks about 4 Gy + 0.5 Gy
for earth’s formation => about
4.5 Gy for earth’s age
Relative Ages
• Oldest regions of crust:
Central regions of
continents (few Gy)
• Youngest regions of crust:
Seafloor (few hundred My)
–Upwelling of materials from
mantle by convection
–Constantly renewed
–Migration of continents
Mercury: Surface
• Cratered highlands (4 Gy old)
• Large impact basins, plains
with few craters (3 Gy old)
• Ratio volcanic/cratered terrain
about 0.3; same as moon’s ratio
=> evolution similar to moon’s
• “Dead” planet now
Venus: Surface
• Highlands: Volcanic and local
(not global!) tectonic rises
• Lowlands: Undulating lava
plains
• Ratio volcanic/cratered about
4; similar to earth’s ratio;
surface evolved as much as
earth’s
Mars: Surface
• Lowlands: Cratered southern
hemisphere (wind erosion now;
water erosion in past))
• Highlands: Volcanic regions in
northern hemisphere (2 Gy old)
• Ratio volcanic/cratered about
0.7; between moon and earth
Interiors
• Moon: Rocky core; cool
• Mercury: Large cold metal core,
thin rocky mantle
• Mars: Small metal core, large
rocky mantle
• Venus: Large hot metal core;
interior much like earth’s
Comparative Evolution
• Mass matters!
• More mass, greater internal
energy from formation,
radioactive decay
• More mass, greater size
(volume), ratio mass/surface
area less, lower rate of heat
loss, longer evolution
Evolution
• Formed by accretion of smaller
bodies; melted, differentiated
• Crust solidified; cratered by
impacts; basins formed (filled
by volcanism, water on earth)
• Loss of internal energy: End of
evolutionary life