Transcript magnetic field

Chapter 891011 Part 2
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)
Shield Volcanoes
Shield volcanoes
are found above
hot spots.
Fluid magma
chamber, from
which lava erupts
repeatedly through
surface layers
above.
Shield Volcanoes and Plate tectonics
Tectonic plates moving over hot spots producing
shield volcanoes result in chains of volcanoes
Example: The
Hawaiian Islands
All volcanoes on
Venus and Mars
are shield
volcanoes
Tectonic plates
DO NOT occur on
Venus and Mars
This is beginning to
look to be true for
Mercury, too.
Volcanism appears to be responsible for formation of
Mercury’s widespread plains
2009
Pancake domes are volcanoes that erupted thick
molten rock.
~25 km in diameter, but only 1-2 km high.
Similar to shield volcanoes in Hawaii,
but thicker lava.
Volcanoes on Venus
Sapas Mons (radar image)
Many volcanoes,including
both shield volcanoes and
stratovolcanoes
~ 400 km (250 miles)
2 lava-filled calderas
Lava flows
Volcanoes on Mars
Highest and largest volcano
in the Solar System.
Tharsis volcanoes
Olympus Mons
Valleys
NASA
Coronae: Circular bulges formed by
volcanic activity
300 km across
Venus is the only
planet known to
have coronae.
(concentric tectonic
stretch marks
formed by hot
rising plumes
from the mantle)
outward pressure
from upwelling
mantle material
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
Jupiter’s Moons
64 known; new ones are still being discovered.
Four largest moons already discovered by Galileo:
The Galilean moons
Io
Europa
Ganymede
Callisto
Io: Bursting Energy --> Volcanic Activity
Io
Europa
Ganymede
Callisto
Ganymede: A Hidden Past
Largest of the 4 Galilean moons.
• Av. density = 1.9 g/cm3
•Rocky core
•Ice-rich mantle
•Crust of ice
Bright terrain probably
formed through flooding
when surface broke
Ganymede
• Largest moon in the solar
system
• Clear evidence of geological
activity
• Tidal heating plus heat from
radio-active decay?
Io
Europa
Ganymede
Callisto
Callisto: The Ancient Face
Heavily cratered --> OLD
No metallic core: possibly silicate core
Layer of liquid water, ~ 10 km thick, ~ 100 km below surface, probably heated
by radioactive decay.
Callisto
Saturn’s moon: Titan’s Surface
• Huygens probe provided first look at Titan’s
surface in early 2005
• Liquid methane, “rocks” made of ice
The Moons of Uranus
5 largest moons are visible from Earth.
5 largest moons all tidally locked to Uranus.
Interiors of Uranus’s Moons
Large rock cores surrounded by icy mantles.
Uranus’s Moon Miranda
Most unusual of the 5 moons detected from Earth
Ovoids: Oval groove patterns,
probably associated with
convection currents in the
mantle, but not with impacts.
20 km high cliff near the equator
Surface features are old; Miranda
is no longer geologically active.
Neptune’s Moon Triton
• Similar to Pluto, but
larger
• Evidence for past
geological activity
Theoretical Techniques for Calculating Interior Conditions
Equation of State ( P, T, rho):
dP  g* dz
and for geologists changes of state (melting and solidifyng)
is important to understand minerals

Differentiation: the process by which homogeneous material
gets divided into masses of different composition and physical
properties
Differentiation: the process by which homogeneous material
gets divided into masses of different composition and physical
properties
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
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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