Chapter 22: Planetary Geology
Introduction
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Compositional Groups:
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Gases:
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Rocks:
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H & He
Melting points near absolute zero (-273°C)
Silicate minerals & Fe-Ni metal
Melting points >700°C
Ices:
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Composed of Ammonia (NH3), Methane (CH4), CO2 & H2O
Intermediate melting points
The Planets
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Inner Planets:
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AKA Terrestrial Planets (like Earth)
AKA Rocky Planets
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Mercury, Venus, Earth, Mars
Outer Planets:
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Dominated by rocky materials
AKA Jovian Planets (like Jupiter)
Gas Giants: Jupiter & Saturn
Ice Giants: Uranus & Neptune
+ Pluto (Rocky-Ice planet?)
Minor Planets:
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Asteroids, Comets & Kuiper Belt Objects
Planetary Data
Planetary Atmospheres
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Ability to hold onto an atmosphere depends on
planet’s mass & temperature
Escape velocity: minimum velocity to escape the
gravity of a plant
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e.g. Earth’s escape velocity = 11 km/s
Ice line: distance from Sun that is cold enough for
water ice to be stable
Giant planets have thicker atmospheres b/c formed
past ice line & therefore accreted ices & rock
Inner planets have thinner atmospheres b/c
accreted only rock
Mercury
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Low albedo
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Has highly-crated
highlands & smooth
terraines similar to Moon
Highly eccentric orbit
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46-70 million km
High density
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Reflects only 5% of sunlight
Implies large core
Tidally locked to Sun
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3:2 resonance
3 days to 2 years
http://www.nineplanets.org/mercury.html
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Irregularities in
Mercury’s orbit helped
to prove Einstein’s
General Theory of
Relativity
Radar Map
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Due to high cloud cover
Second brightest object
in night sky
Nearly circular
retrograde orbit
Thick atmosphere
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Venusian Surface
High albedo
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Venus
90 atm
~470°C (melt Pb)
Pancake volcanoes
http://www.nineplanets.org/venus.html
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Considered Earth’s
twin
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95% Earth’s diameter
80% Earth’s mass
Young surfaces
Same bulk chemistry &
density
Earth-Moon System
http://www.nineplanets.org/moon.html
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Brightest object in night sky
Two types of terraines:
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Ancient highlands
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Younger Maria
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~ Basalt
Low density (~3.3 g/cm3)
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~ Feldspar
Implies little or no core
Formation by large impact
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~Mars-sized object
Explains O-isotopes, low
density & chemical
composition
cygnus.colorado.edu
Mars
Viking Image
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1% Atm of Earth
 CO2 rich
Ice caps (H2O & CO2)
Evidence of liquid water
Has highest mt. & longest,
deepest valley in Solar
System
Phobos
Deimos
http://www.nineplanets.org/mars.html
Pathfinder Image
Jupiter
http://www.nineplanets.org/jupiter.html
Io
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Largest planet in Solar System
Bands of clouds & storms
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Convection of atm
Radiates more heat than receives
from Sun
Rotates in 10 hours
At least 28 moons
Europa
Saturn
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Second largest planet in Solar
System
Has well-developed ring
system
Bands & storms
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Similar to Jupiter’s
At least 30 moons, including
“sheppard moons”
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Titan has thick atmosphere
Titan
Mimas
http://www.nineplanets.org/saturn.html
Uranus
Rings
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Twin with Neptune
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Rotates 90° to orbit
around Sun
At least 15 moons
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Slightly larger in diameter
Slightly smaller in mass
Miranda shows greatest
At least 9 rings
http://www.nineplanets.org/uranus.html
Miranda
Neptune
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Twin with Uranus
Blue due to methane in
atmosphere
Bands & storms
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Giant Dark Spot has disappeared
At least 13 moons
Triton has atmosphere
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Retrograde orbit
Similar in reflectance spectra to
Kuiper Belt Objects & Pluto
Ice volcanoes
Triton
http://www.nineplanets.org/neptune.html
HST image
Pluto-Charon System
HST image
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Highly eccentric & inclined
orbit
Highest satellite:planet
radius ratio
Similar reflectance spectra
to Kuiper Belt Objects
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Also to Centaurs & primitive
asteroids
Charon
http://www.nineplanets.org/pluto.html
Minor Planets
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Asteroids:
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Kuiper Belt Objects:
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Mostly between Mars & Jupiter
AKA Trans-Neptunian Objects
Discovered in 1992
Source of Short-Period Comets
Oort Cloud Comets:
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Spherical Cloud on edge of Solar System
Theoretical, proposed in 1950
Source of Long-Period Comets
Asteroids
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First discovered in 1801
 Named Ceres
Several hundred thousand
have been discovered
 Several 1000 discovered
each year
Classified by composition &
albedo
 75% are C-type
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243Ida
951Gaspara
253Mathilde
http://www.psi.edu
17% are S-type
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Darkest, C-rich
http://www.nineplanets.org/asteroids.html
Moderate, metal + silicates
5% are M-type
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Brightest, mostly metal
Itokawa
http://near.jhuapl.edu/iod/20000214f/index.html
433Eros
Kuiper Belt Objects
Quaoar
Sedna
en.wikipedia.org/wiki/50000_Quaoar
http://hubblesite.org/newscenter/archive/releases/2004/14/image/a
Oort Cloud Comets
www.solstation.com
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~50,000 AU from Sun
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~ 1 light year
Source of long period
comets
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www.wikipedia.com
> 200 years
Materials scattered out
from interaction with
Jupiter & Saturn
www.britannica.com
gatornet.chapin.edu
Meteorites: Time Capsules
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Nebula Heterogeneous
Formation Sequence
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CAIs, Chondrules, fine-grained materials
Some melted
Some wet
Some hot
Some both hot & wet
Organic materials present
Meteorite Classification
Metallic
Achondrites
Chondrites
Igneous
Primitive
Basaltic
Pallasites
Carbonaceous
Ordinary
Enstatite
Chondritic ~ Solar Composition
Martian Meteorites
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Are probably from Mars b/c:
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Young & basaltic
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O-isotopes:
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Recent volcanism (130 to 1300 Ma)
if one from Mars, all from Mars
Gas bubbles trapped in glass
Composition ~ Viking measurements
 N2, CO2, H2, He, Ar, Kr, Xe & isotope ratios
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Life on Mars?
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Carbonate Globbules
~900oC or <80oC ?
Also: PAHs
~ Antarctic meltwater
Not spatially near CO3’s
Orange: Ca, Mn-rich
Inner Black: Mg-rich
White: Fe-rich
Outer Black: Fe, S-rich
(where mt is)
Oxygen Isotopes
Shergotty
Life on Mars?
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SEM prep
artifact?
Too small for
DNA?
Terrestrial
contamination
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Life on Mars?
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ALH84001
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Terrestrial
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Etched Volcanic Glass