ASTR 100
Lecture 9: Terrestrial Planets I:
Planetary Geology
Reading Ch. 6, 7 in “Essential”
Whirlwind tour of our Solar system…
All described by Newton’s law of Motion w/ gravity
as the Force, (but not necessarily Kepler’s laws)
A couple of non-Keplerian things…
Touring our solar system:
We understand motion (thank you Kepler and Newton).
For each set of objects, we’ll ask two basic questions:
1) Classify the object’s structure
2) Classify the object’s evolution
Inner planets, or Terrestrial planets
Rocky, atmospheres, few moons
0.4-5 AU
Moon: “Terrestrial planet” in composition,
“Moon” because of orbit.
https://www.youtube.com/watch?v=BNtknTrMWZE
Inner planets characterized by, layered,
rocky body and (maybe) atmosphere,
(maybe) magnetosphere
Denser materials at the
center, fluffier materials
to the outside:
Differentiation is the process
of more dense matter sinking
and less dense matter rising
http://www.youtube.com/watch?v=wbwi-jMygZ8
http://www.youtube.com/watch?v=dQArxmdD5YI
Structure: Similarities/differences between the
terrestrial planets:
Evolution: Internal and external forces shape planets
Internal:
Volcanism
Tectonics
Weather (Erosion)
External:
Collisions
Tidal influences
Space weather
Terrestrial planets come in two flavors:
Moon and Mercury: “Geologically dead”
Venus and Earth: “Geologically alive”
Mars: “Almost dead”
Why?
“Lithosphere” the solid part of the mantle
*Not to scale on Earth and Venus
-Thick lithosphere means no Volcanism and
no Seismic activity
-Smaller planets have thicker lithospheres
Thick lithosphere means
No Volcanism and No Seismic activity
Smaller planets cool faster
http://www.youtube.com/watch?v=Jmk6_6Eac5o
Sources of heat:
Contraction
Differentiation
Radioactivity
Accretion
Sunlight NOT a significant source of heat
Lava plains on the Moon
Evidence for ancient Volcanic activity
Old tectonic activity on Mars
Evidence of weathering on Mars.
…continuing weathering on Mars!
Key Terms:
Terrestrial planets, differentiation, core, mantle, crust,
atmosphere, lithosphere
Key Ideas:
What features do all terrestrial planets share?
Why do we sometimes talk about our moon as a
terrestrial “planet”?
What types of processes shape terrestrial planets?
What does it mean to be “geologically alive” or
“geologically dead?”
Why are some terrestrial planets “geologically dead”
and others “geologically alive”?