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Chapter 891011 Part 3
Planets in General
Standard Plane
Comparative Planetology
Hartmann: Chapters 8 Planetary Interiors
9 Planetary Surfaces
10 Planetary Surfaces
11 Planetary Atmospheres
Comparative Planetology
Formation history
Interior
geological activity
Atmosphere
atmospheric activity
Magnetic field
magnetic field activity
Role of Planetary Size
Role of Distance from Sun
Role of Rotation
Comparative Planetology
Formation history
Interior
geological activity
Four basic properties of a planet:
mass
diameter
mean density
surface rock properties
Basic concept is to use the surface features & materials as
observational boundary conditions & then reason out the interior
of the planet based on our knowledge of how these materials
behave under high pressure and how resulting surface features
are formed.
Processes that Shape Surfaces
A. Impact cratering
Impacts by asteroids or comets
B. Volcanism
Eruption of molten rock onto surface
C. Tectonics
Disruption of a planet’s surface by internal
stresses
D. Erosion
Surface changes made by wind, water, or ice
Comparative Planetology
Craters
Volcanoes
Cliffs
Mountains
Plains
Ice Caps
Magnetic field
Axis tilt
Impact Cratering
Volcanism (lava, outgassing)
Cliffs
Mountains
tectonics
Plains
Ice Caps
Magnetic field
Rotation
Distance from Sun
Heating /Cooling of Interior
Erosion (water, ice, wind, debris)
Source of volcanism ….
Core, Mantle, Crust, Atmosphere
All terrestrial planets have a similar structure:
… a liquid core
… a mantle of molten lava
… a crust od solid,
low-density rocks
… an atmosphere
(large range of
compositions and
pressures)
Comparative Planetology
Craters
Volcanoes
Cliffs
Mountains
Plains
Ice Caps
Magnetic field
Axis tilt
Impact Cratering
Volcanism (lava, outgassing)
Cliffs
Mountains
tectonics
Plains
Ice Caps
Magnetic field
Rotation
Distance from Sun
Heating /Cooling of Interior
Erosion (water, ice, wind, debris)
The Highlands on the Moon
Saturated with craters
Older craters partially
obliterated by more
recent impacts
… or flooded
by lava flows
mi
6.68
5.45
2.97
1.74
-0.74
-3.21
-5.69
Hadley Rille-Apennine mountain region at 26 deg 06 min 54 sec N, 3 deg 39 min 30
sec E on the lunar surface. The lunar module (LM) carrying astronauts David Scott
and James Irwin and the lunar roving vehicle (LRV) landed on the moon on July 31,
1971. http://www.penpal.ru/astro/Apollo15.shtml
“lobate scarps” are long, steep curved cliffs, probably
formed when Mercury shrank while cooling down
Discovery Scarp
Discovery scarp
500 km long,
2 km high
Mercury’s crust split
and cracked as the
planet cooled and
shrank
lobate scarps
Two Geological features on Mercury worth mentioning:
2. lobate scarps are landforms on Mercury that
appear to have formed by thrust faulting and are
thought to reflect global contraction due to cooling
of the planet's interior (like a drying apple)
“Radargraphs”
Using radar, the topography (surface features) of
Venus is imaged.
Radar images showed a relatively flat Venus with some
highlands; two continental-sized areas of higher
elevation; …terrain is comprised of:
10% mountain, 70% upland plains, 20% lowland plains
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
Role of Planetary Size
Role of Distance from Sun
Role of Rotation
• Smaller worlds cool off faster and harden earlier
• Larger worlds remain warm inside, promoting
volcanism and tectonics
• Larger worlds also have more erosion because their
gravity retains an atmosphere
Role of Planetary Size
Role of Distance from Sun
Role of Rotation
Role of Planetary Size
Role of Distance from Sun
Role of Rotation
• Planets close to Sun are too hot for rain, snow,
ice and so have less erosion
• More difficult for hot planet to retain atmosphere
• Planets with liquid water have most erosion
• Planets far from Sun are too cold for rain,
limiting erosion
Role of Planetary Size
Role of Distance from Sun
Role of Rotation
Habitable Zone for Constant Liquid Water in the
Solar System
Role of Planetary Size
Role of Distance from Sun
Role of Rotation
Slow rotation
Fast rotation
• Planets with slower rotation have less weather
and less erosion and a weak magnetic field
• Planets with faster rotation have more weather
and more erosion and a stronger magnetic
field
Other Observational that Check the Models for Planet Interiors:
moment of inertia … kMR2 , k being coefficient of … {0. 1.}
geometric oblateness … reflects mass distribution or departure
from hydrostatic equilibrium
form of gravitational field
rotation rate … necessary for moment of inertia, geometric
oblateness
surface heat flow
composition of neighbors (planets and or meteorites)
magnetic field … strong field indicates a flluid core
drilling and direct sampling
Earth
seismic properties
}
Comparative Planetology
Craters
Volcanoes
Cliffs
Mountains
Plains
Ice Caps
Magnetic field
Axis tilt
Impact Cratering
Volcanism (lava, outgassing)
Cliffs
Mountains
tectonics
Plains
Ice Caps
Magnetic field
Rotation
Distance from Sun
Heating /Cooling of Interior
Erosion (water, ice, wind, debris)
The Earth’s Magnetic Field is
created in the same way you
make an electromagnet
In an electromagnet
the electrons move
around an iron nail
education.gsfc.nasa.gov/nycri/units/pmarchase/
A planet with a magnetic field indicates a fluid
interior in motion
• Planetary magnetic fields
are produced by the motion
of electrically conducting
liquids inside the planet
• This mechanism is called a
dynamo
• If a planet has no magnetic
field, that is evidence that
there is little such liquid
material in the planet’s
interior or that the liquid is
not in a state of motion
• The magnetic fields of
terrestrial planets are
produced by metals such
as iron in the liquid state
• The stronger fields of the
Jovian planets are
generated by liquid
metallic hydrogen or by
water with ionized
molecules dissolved in it
Main Worlds with Active Magnetic Fields
Strength Order:
Sun, Gas giants, Earth, Mercury, Mars (remnant)
The Earth is made of four layers
The Crust:
A Thin Rock Material
The Mantle:
A Dense and Mostly Solid
Rock Material
The Outer Core:
Liquid Iron and Nickel
The Inner Core:
Solid Iron and Nickel
The Iron Core of the Earth is an
Electromagnet
The core is surrounded by
liquid Iron and Nickel
As electrons flow around
the core the magnetic field
is produced
The Earth’s rotation
makes the electrons flow
at very high speeds
Magnetic Fields on Other Planets in
our Solar System
Planet
Magnetic Field
Mercury
100 times weaker than Earth
Venus
25,000 times weaker than Earth
Earth
30,000 – 60,000 nT
Mars
5000 times weaker than Earth
Jupiter
20,000 times greater than Earth
Saturn
540 times greater than Earth
Uranus
40 times greater than Earth
Neptune
¼ that of Earth
Pluto
None that we know of
Mercury
Mercury has a weak magnetic field.
This suggests Mercury has an iron
core with liquid interior.
The weak magnetic field could be the
result of the slow rotation period.
Venus
Venus has a very weak magnetic field.
(About 25,000 times weaker than Earth’s)
Venus appears to lack the necessary
ingredients to generate a magnetic field
(no liquid core?)
Venus also has very slow rotation.
Mars
Mars also has a very weak magnetic
field.
(About 5,000 times weaker than
Earth’s)
The interior of Mars appears to have
cooled so much that it is no longer
liquid.
• The volcanoes in Mars are no
longer active
• There is no Earthquake activity on
Mars
Jupiter
Jupiter has a strong magnetic field.
(About 20,000 times stronger than
Earth’s)
The Terrestrial planets generate
magnetic fields from iron at the
center.
But Jupiter has almost no iron core.
The magnetic field of Jupiter is
produced by the motion of liquefied
metallic hydrogen found beneath the
surface.
Saturn
Saturn also has a strong magnetic field.
(About 540 times stronger than Earth’s)
Saturn’s magnetic field is produced in the
same way Jupiter’s is.
Uranus
The magnetic field in Uranus is
about 40 times stronger than Earth’s
It is probably created in the core of
the planet, with ice, rather than with
iron.
Neptune
The magnetic field in Uranus is
about 1/4 times as strong as Earth’s
It is probably created in the same
way as Uranus
Pluto
We do not know if Pluto has a
magnetic field.
Because Pluto has a small size and a
slow rotation rate (1 day in Pluto = 6.4
Earth days), it does not seem likely that
Pluto has a magnetic field.