Download Geology of the Moon Geology of Mercury

Geology of the Moon
• Smooth, dark lunar
maria are less heavily
cratered than lunar
highlands
• Maria were made by
flood of runny lava
• Wrinkles arise from
cooling and
contraction of lava
flood
• heavily cratered, no
atmosphere (too
small), geologically
inactive
Geology of Mercury
• A mixture of heavily cratered and smooth regions like the Moon
• Smooth regions are likely ancient lava flows
• Tectonics: Long cliffs indicate that Mercury shrank early in its
history
• No atmosphere (too small), geologically dead
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Geology of Mars
• mountains & canyons
• Valles Marineris
• volcanoes
• thin atmosphere
(CO2)
• no plate tectonics
• evidence for water
erosion
Cratering on Mars
• Amount of cratering differs greatly across surface
• Many early craters have been erased
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Volcanism on Mars
• Mars has many
large shield
volcanoes
• Olympus Mons is
largest volcano in
solar system
Tectonics on Mars
• System of valleys known as Valles Marineris
thought to originate from tectonics
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Dry Riverbeds?
• Close-up photos of
Mars show what
appear to be driedup riverbeds
• Details of some
craters suggest they
were once filled
with water
• Mars rovers have
found rocks that
appear to have
formed in water
Water on Mars?
• Some craters have frozen water exposed for short period
• There is evidence for (frozen) water within 1 meter under
the surface
• this underground water may be all over the planet
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Ancient Water on Mars
• Liquid water can not exist on Mars today.
• temperatures below freezing
• air pressure too low
• Dry river channels in southern highlands
• heavily cratered terrain (> 3 billion years old)
• Some surface features
are eroded.
• implies running
water, rain
• crater lakes
• Mars was warm & wet
over 3 billion years ago.
Recent Water on Mars?
• Liquid water could exist temporarily with today’s
temperatures and air pressures…in a flash flood!
• Underground water seeps out to form erosion gullies
• these gullies were observed on a crater wall
• at their size, sandstorms would cover them in few million
yrs
• such floods have occurred within the last few million years
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Martian Weather Today
• Seasons on Mars are more extreme than on Earth
• CO2 condenses & sublimes at opposite poles
• changes in atmospheric pressure drive pole-to-pole winds
• sometimes cause huge dust storms
Martian Weather: N Polar Ice Cap & Dust Storm
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Climate Change on Mars
• Mars has not had
widespread surface
water for 3 billion
years
• Greenhouse effect
probably kept
surface warmer
before that
• Somehow Mars lost
most of its
atmosphere
Climate Change on Mars
• Magnetic field may have preserved early Martian
atmosphere
• Solar wind may have stripped atmosphere after field
decreased because of interior cooling
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Geology of Venus
• Has a thick, cloudy
atmosphere -- you can not
visually see the surface
• we must image the surface
using radar
• smooth plains with few
mountain ranges
• few craters
• many volcanoes and domes
of lava (corona)
• Venus is very active with
tectonics & volcanism
Volcanism & Tectonics on Venus
• Impact craters are randomly spread over Venusian
surface.
• implies that the planet’s entire surface is the same age
• crater counting suggests an age of 0.5 billion years old
• Volcanism “paved over” the surface 1 billion years ago.
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Erosion on Venus
• Photos of rocks show little erosion. This means no wind, rain, or
ice on the surface.
• The surface of Venus is very hot (430 C)… too hot for liquid or
ice to exist
• Venus rotates very slowly (P = 243 days), so no wind is
generated
Does Venus have plate
tectonics?
•
•
•
Most of Earth’s major geological features can
be attributed to plate tectonics, which
gradually remakes Earth’s surface
Venus does not appear to have plate tectonics,
but entire surface seems to have been
“repaved” 750 million years ago
Possibly this is a cyclic process that cools
interior
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Atmosphere of Venus
• Thick carbon dioxide atmosphere
with produces a strong
greenhouse effect
• Earth escapes this fate because
most of its carbon and water is in
rocks and oceans
• Surface pressure 90 times Earth’s
• Slow rotation produces very little
weather
• Reflective clouds contain droplets
of sulphuric acid
Climate History of Venus
• Venus should have outgassed as much H2O as Earth.
• Early on, when the Sun was dimmer, Venus may have
had oceans of water
• Venus’ proximity to the Sun caused all H2O to
evaporate.
• H2O contributed to runaway greenhouse effect
• surface heated to extreme temperature
• UV photons from Sun dissociate H2O; H2 escaped,
O stripped
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Summary
• What are terrestrial planets like on the inside?
– Core, mantle, crust structure
– Denser material is found deeper inside
• How do interiors get hot or cool down?
– Radioactive decay is currently main heat source
– Cooling occurs due to convection, conduction and
radiation
– Interior heat drives geological activity
• Why do some planetary interiors create magnetic
fields?
– Requires motion of charged particles inside planet
Summary
• What processes shape planetary surfaces?
– Cratering, volcanism, tectonics, erosion
– Amount of cratering tells us how long ago a
surface formed
• Why do the terrestrial planets have different
geological histories?
– Differences arise because of planetary size,
distance from Sun, and rotation rate
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Summary of Geology of Planets
• How do we know that Earth’s surface is in motion?
– Measurements of plate motion confirm idea of
continental drift
• How is Earth’s surface shaped by plate tectonics?
– Plate tectonics responsible for subduction,
seafloor spreading, mountains, rifts, and
earthquakes
– Reason for plate tectonics still a mystery
Summary
• How did Earth’s atmosphere end up so different?
– Temperatures just right for oceans of water
– Oceans keep most CO2 out of atmosphere
– Nitrogen remains in atmosphere
– Life releases some oxygen into atmosphere
• Why does Earth’s climate stay relatively stable?
– Carbon dioxide cycle acts as a thermostat
• How might human activity change our
planet?
– Destruction of ozone
– High rate of extinction
– Global warming from production of
greenhouse gases
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Summary of Geology of Planets
• What geological processes shaped our Moon?
– Early cratering still present
– Maria resulted from volcanism
• What geological processes shaped Mercury?
– Cratering and volcanism similar to Moon
– Tectonic features indicate early shrinkage
Summary of Geology of Planets
• What are the major geological features of Mars?
– Differences in cratering across surface
– Giant shield volcanoes
– Evidence of tectonic activity
• What geological evidence tells us that water once flowed on
Mars?
– Features that look like dry riverbeds
– Some craters appear to be eroded
– Rovers have found rocks that appear to have formed in
water
– Gullies in crater walls may indicate recent water flows
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Summary
• What is Mars like today?
– Mars is cold, dry, and frozen
– Strong seasonal changes cause CO2 to move
from pole to pole, leading to dust storms
• Why did Mars change?
– Its atmosphere must have once been much
thicker for its greenhouse effect to allow
liquid water on the surface
– Somehow Mars lost most of its atmosphere,
perhaps because of declining magnetic field
Summary of Geology of Planets
• What are the major geological features of Venus?
– Venus has cratering, volcanism, and tectonics but
not much erosion
• Does Venus have plate tectonics?
– The lack of plate tectonics on Venus is a mystery
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Summary
• What is Venus like today?
– Venus has an extremely thick CO2
atmosphere
– Slow rotation means little weather
• How did Venus get so hot?
– Runaway greenhouse effect made Venus too
hot for liquid oceans
– All carbon dioxide remains in atmosphere,
leading to a huge greenhouse effect
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