Lecture 13 Geology of the Inner Planets - January 7b, 2014
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Lecture 13
Geology of the Inner Planets
January 7b, 2014
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Clues to the Interior Structure of
Planets
• Mean (Average) Density
Mean Density
Mass
Volume
kg m 3
– Water ~1000 kg/m3
– Rocks ~2000-4000 kg/m3
– Metals ~7000-10000 kg/m3
– Compare average density to known densities
– The mean density of the Earth is 5500 kg/m3
3
Clues to the Interior Structure of
Planets
• Many planets act like a
magnet
• Magnetic field caused
by a dynamo.
• To produce a magnetic
field you need an
electrical conductor that
is liquid and spinning
quickly
4
The Earth’s Magnetosphere
5
The Van Allen Belts
• Magnetosphere
traps charged
particles emitted
from the Sun in
region called
Van Allen Belts
– Traps high-
energy protons
and electrons
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Aurora
• If solar activity is
strong, some
particles will leak
into the atmosphere
causing aurora
(Northern and
Southern Lights)
7
Structure of the Earth
• Average density ~ 5500 kg/m3
• Earth mostly rock and metal
– Silicon, iron, and oxygen very common.
• Interior structure
of Earth can be
determined by
looking at how
earthquake waves
move through the
Earth.
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Interior Structure of the Earth
• Crust: thin, rocky
• Mantle:basalts
• Outer core: Liquid
iron and nickel
– Determined by
seismic studies
– Creates magnetic
field
• Inner core: Solid iron
and nickel
9
Plate Tectonics on the Earth
• Lithosphere = solid crust and upper mantle.
• Mantle further down is more plastic and can flow.
• Lithosphere is fractured into many plates floating
on denser mantle material
10
Continental
Drift11
Geologic Activity on the Earth
• Most activity occurs near plate boundaries
– Earthquakes
– Volcanism12
Earth’s magnetic field originates in
A. a solid, permanently magnetized core.
B. the polar regions of the magnetosphere.
C. currents of molten iron deep inside the planet.
D. intense electric currents in the Van Allen belts.
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Mercury
• Likely geologically
dead, but at least
some of its core
is liquid
• Many craters
– Highlands ~ 3.8 byrs old
– Intercrater plains ~ older than 3 byrs old
NASA's Mariner 10 spacecraft made its first flyby of Mercury in March 1974, and was also the only Mariner mission
to visit two planets (the other was Venus).
Images beamed back by the spacecraft from 437 miles above the planet revealed a surface very similar to that of the
moon. However, Mariner 10 only had enough time to map half of the planet -- which is a big reason why NASA
recently sent their MESSENGER spacecraft to Mercury.14
Mercury Messenger
http://www.nasa.gov/mission_pages/messenger/main/index.html
http://en.wikipedia.org/wiki/MESSENGER
• Launched August 2004
• Arrived 2011
• Found water and water
ice
• Obtained visual
evidence of past
volcanic activity
• Determined the
planetary core is
partially liquid
http://messenger.jhuapl.edu/the_mission/artistimpression/atmercury_br.html15
Messenger Fly-by August 2, 2005
http://en.wikipedia.org/wiki/File:Mdis_depart_anot.ogv16
Interior Structure of Mercury
• = 5430 kg/m3 (similar to Earth)
• Earth is only denser because of gravitational compression
– Mass of Earth is greater
– Metals compressed to higher densities
• Mercury has
proportionally much
more metal.
• Weak magnetic field
(1/100 of Earth’s)
little molten metal OR
due to slow spin17
Interior Structure
• Earth uncompressed = 4400 kg/m3
• Mercury uncompressed = 5300 kg/m3
– Mercury formed closer to the Sun, where
higher temperature favored the condensation of
heavier, metallic elements18
The central core of Mercury is probably composed of
A. water and CO2 ices.
B. molten rock.
C. solid rock.
D. solid or molten iron.
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Interior Structure of Venus
• Mass, size and density (5340 kg/m3) similar
to Earth
Composition and internal structure likely similar
• No magnetic field
– Due to slow rotation?
– Pspin= 243 days20
Venus – Magellan Radar Map
Color = elevation. Blue areas are NOT liquid oceans, just low-lying areas21
No Plate Tectonics
• No long ridges or faults indicating plate tectonics
• Many local deformations of surface, but not due to
plate tectonics22
Why No Plate Tectonics?
1. Thin lithosphere – could not support
large-scale tectonics so only local
deformations were created.
2. Thick lithosphere
• Not broken into sheets.
• Mantle material not moving enough to move
sheets of material.23
Volcanoes on Venus
• Over 1600 major volcanoes observed
• Many similar to shield volcanoes on the
Earth (e.g. Hawaii)
• May currently
be active
• Sulfur dioxide
in atmosphere
.
Image 83 x 73 km24
Alpha Regio (Venus)
Hill Diam ~25 km
Height ~750 m25
Coronae
• Large up-welling Boann Corona
of mantle
• Volcanoes in and
around coronae
• Unique to Venus
Diameter: 225 km26
Lava Channels, Lo Shen Valles
~22x27 km27
Craters on Venus
• ~1000 craters have
been observed on
surface.
– Randomly distributed
on surface = surface
all about the same age.
– Surface about 500
million years old.28
Venus and Earth have similar
A. mass, density, and surface temperature.
B. mass and density.
C. mass, density, and magnetic field.
D. magnetic field, surface temperature, and
atmosphere.
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Composition of Mars
• No global magnetic field
• Pspin= 24.6 hours
• = 3900 kg/m3
– no metal in core or
– metal in core is not liquid
interior is mainly rock.30
General Surface Features
• Northern Hemisphere =
“lowlands”
– Few craters = younger
surface
– Lower average elevation
– Evidence for geologic
activity
• Southern Hemisphere =
“highlands”
– Many craters = much
older surface
– Age ~3-4 byrs
Google Mars Map31
Volcanoes on Mars
• Volcanoes mainly found in Northern Hemisphere.
• Largest = Olympus Mons, largest volcano in solar system!
– Diameter = 600 km
– Height = 24 km
– Very few craters on surface
– Possibly younger than 100 million years!
• No evidence for plate tectonics
• Volcanoes likely formed by hot-spot volcanism32
Tharsis Region
Twelve orbits a day provided the
Mars Global Surveyor MOC wide
angle cameras a global snapshot of
weather patterns across the planet
in April, 1999. Here, bluish-white
water ice clouds hang above the
Tharsis volcanoes. This computer
generated image was created by
wrapping a global map onto a
sphere. The center of this sphere is
15 degrees North latitude, 90
degrees West longitude. This
perspective rotates the south pole
(which has no data coverage in the
original map) away from our field
of view. Courtesy NASA33
Olympus Mons
• Size of Missouri
• 3 times height of
Mt. Everest.34
Tharsis Volcanoes
This is a shaded relief image
derived from Mars Orbiter
Laser Altimeter data, which
flew onboard the Mars Global
Surveyor. Courtesy NASA35
Valles Marineris
• Large canyon
(fracture?) in crust
• 1/5 circumference
of planet
• 7 km deep
• 4 minute tour
http://marsprogram.jpl.nasa.gov/gallery/atlas/36
Mars has a rotation period of 24.6 hours and a density of
3900 kg/m3 but it has no global magnetic field. What is its
most probable interior composition?
A. Very little metal, solid rock.
B. Very little metal, molten rock.
C. Mostly molten metal but with solid rock.
D. Mainly molten metal and molten rock.
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