Mars, the Moon, and the Earth
11/28/2012 10:53:00 PM
Class 11/28/12
 Synthesis of terrestrial bodies
o Terrestrial planets
 Tectonics and geological style are related to methods of
heat transfer and the evolution of the interior
 One plate planets
 Mars, moon, mercury, no lithospheric renewal and
destruction
 Early heating and expansion, eruption
Later cooling and contraction, inhibition of
eruption
 Themes
 Early bombardment
 Loss of heat by conduction
 Lithosphere thickens with time
 Tectonics predominantly vertical
Multi-plated planet
 Earth
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 Multiple plates
 Seafloor spreading and continental drift
 What about the early history?
 How did it start?
Periodic catastrophic overturn?
 Venus?
 Vertically accreting depleted mantle layer
 Heat transfer
 Mostly lithospheric conduction
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But also could be tectonics and volcanic
heat pipes
Major influences on planetary evolution
 Size
 Heat loss
 Surface area v. volume
 Planetary chemistry
 Iron silica ratio
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Abundance of volatiles
o Maybe a prerequisite for plate
tectonics and definitely for
atmosphere
 Abundance of radiogenic heat sources
 Significance of distance from the sun
Budget of internal/external energy sources
 Accretion and subsequent bombardment
 Radioactivity
 Differentiation
 Tidal interaction
Earth – a comparison
 Significance of bulk properties
 Density
o Earth is denser than others but close
to mercury and venus
 Gravity
 Size
o Similar in size to venus – decently
bigger than mercury and mars
 Distance from sun
 Presence of satellites
Major influences on planetary evolution
 Heat is likely the key
 What are heat sources?
o Primordial accretion
o Impact related
o Radioactive decay
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o Core formation
o External tidal sources
 Interplay of heat production and loss is
thermal evolution
Perspectives on earth
 First half of solar system history
 Impact cratering – extinctions

Crustal formation – magma ocean on moon,
venus?
 Tectonics – plate recycling is not the only
way
 Planetary atmospheres – why is earth
different?
 Environment for conditions that might have
led to life
o Comets, asteroids, meteors
 Asteroid belt between mars and Jupiter
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Metors more like terrestrial planets
Asteroids more like building blocks – like outer planets
Comets more like volatiles in cold storage in outer solar
systems
Hard to flyby asteroids – very small
 Idea of a dense asteroid belt is fiction
Comet Hale-Bopp
Origins of comets
 Oort cloud
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 Why
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Asteroids
 Size
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Many billions of comets
Out by pluto
the tail?
Dust entrained in escaping gas
Jets of sublimating gas in sunward side
Original dirty ice
>500 km
 some bigger
location
 between mars an Jupiter
 some closer
 some farther
data available
 telescopes
 Galileo (gaspara, ida)
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 NEAR (matilda, eros)
Age
 Presumed ancient…
Composition
 Diverse
 Some asteroids even have satellites
o Ida and Dactyl
Origin and evolution
 Most likely prevented from accreting into a
planet by Jupiter
 Some differentiated early some did not
 Order remains in the asteroid belt
Danger?
 Very low incidence rate
 Catastrophic death rate
 Sometimes asteroids fall in cities
o Break roof
o Break car
o One lady in Alabama got hit in the hip
o 1972 earth narrowly missed a 10
megaton impact
11/28/2012 10:53:00 PM
11/28/2012 10:53:00 PM