Terrestrial%20Planets

1
Terrestrial Planets

• Earthlike Worlds of Rocks and Metals

2
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 50-50 metals/rocks

3
Density Layers

• Core (metals)
• Mantle (dense rocks)
• Crust (less dense rocks)
• Partially or fully melted to separate by density
  (differentiation)

4
Internal Energy

• Heat now at surface about 0.1 watt per square
  meter
• Internal energy stored from formation (by
  accretion) plus radioactive decay gt larger in
  past
• Infrared from surface escapes to space, lost
  forever

5
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

6
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 earths
  formation gt about 4.5 Gy for earths age

7
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

8
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 moons ratio gt evolution similar to moons
• Dead planet now

9
Venus Surface

• Highlands Volcanic and local (not global!)
  tectonic rises
• Lowlands Undulating lava plains
• Ratio volcanic/cratered about 4 similar to
  earths ratio surface evolved as much as earths

10
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

11
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
  earths

12
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

13
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