Transcript 16_terrestrials_student

Terrestrial Worlds 1
Mercury
Mercury
• 1974
-Mariner 10 flyby
• 2008-Current
-MESSENGER
Mercury’s
Surface
What is the most
common process
on mercury?
Mercury’s Surface
• A mixture of heavily cratered and smooth
regions like the Moon
• Smoother regions are likely ancient lava flows
Caloris basin
Multi-ring impact basin
(Only half visible
from Mariner 10)
Caloris basin
MESSENGER 2009 -1550km
Volcanism on Mercury
• ancient lava flows, no large floods
Tectonics on Mercury
Cooling causes shrinkage causing fault scarps (cliffs)
Mercury Atmosphere
– 10-14 bars of pressure (negligible)
• Gas comes from impacts that eject surface atoms
Mercury
– Temperatures: 800 oF in day (second hottest)
-300 oF at night
Terrestrial Worlds 2
Venus,
Venus basics
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2nd planet from Sun (0.7 AU), 6th largest world.
Orbit -224 Earth days
Sidereal rotation -243 Earth days (solar day-117 Eds)
Surface gravity-8.8 m/s2 (90% of Earth)
Intense cloud cover - highly reflective in visible light,
surface unseen except by radar
• Spacecraft- Pioneer, Magellan (USA)
Venera 9-16 (Russia)
Highlands on Venus- Aphrodite Terra
Venus - Chasma
Vast mountain and canyon systems.
-3km high and 3km deep running
for thousands of miles
VenusRegios
Regions
Where
canyon
systems
join at a
high volcano
Tectonics
• Downwelling
-Highlands and faulted
regions called tessera
• Upwelling
-Extension rifts at hot spots
= chasmas and regios
Crust too strong to
break all the way
through. No plate
tectonics
Volcanism on Venus
• 80% of Venus is resurfaced by volcanism
• Volcanic shapes controlled by height and
location.
• Hot spots -large shield volcanoes.
• Lowlands - volcanic floods.
• Middling heights- fields of cinder cones.
• High areas - lava too hard to rise - coronae
Venus Surface Processes - Wind
Wind streak showing wind direction
Venus Cratering
• Lots of small to middle-sized craters, few
large ones
• Even distribution -Most of Venus’ surface
has a similar age
• Most of Venus resurfaced by catastrophic
lava flooding < 1 billion yrs ago.
• Current activity??
Venus Atmosphere
• 90 bars of pressure (90 x Earth)
• 96% CO2 3.5% N2 < 1% others
• Massive greenhouse warming.
– Venus is the hottest planet. 870 oF
• Clouds- sulfuric acid!
• Slow rotation - almost no coriolis effect.
Terrestrial Worlds 3
Earth - The most unique of all
Earth basics
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3rd planet from Sun (1 AU), 5th largest world
Orbit - 1 Earth year
Sidereal rotation - 23.9 hours (solar day -24 hrs)
Surface gravity- 9.8 m/s2.
1 bar of pressure
78% N2 21% O2 < 1% others 0.003 CO2.
• Temperatures- ~100oF summer (max. 140oF, deserts)
- ~0 oF winter (min. -130 oF, poles)
Unique Features
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oceans,
Plate tectonics
oxygen atm.
Life!
Earthquakes
Detected earthquakes form lines
Earth’s crust broken into pieces
~8 large and 10 small plates
Crust follows Convection Currents
• Rising current (hot)
• Plate dragged aside
• Breaks at weakest point
(where it is hottest)
• New lava wells into gap.
– DIVERGENT boundary
• Falling current drags plate
after it.
• 1 plate hits another and
sinks.
– CONVERGENT boundary
Earth -tectonics
• All a consequence of internal convection:
– Extension faults occur at upwelling of mid-ocean
ridges (divergent boundary)
– Compression faults occur at downwelling of
subduction zones (convergent boundary)
– Strike-slip faults occur as plates jostle around,
Earth -Volcanism
• All a consequence of internal convection:
– Low viscosity lavas occur at upwelling of mid-ocean
ridges -shield volcanoes
– High viscosity lavas occur at subduction zones as
crust is remelted - tall, explosive, stratovolcanoes
Result: Earth is the ONLY world to have
stratovolcanoes, because it’s the only world to
have plate tectonics
Lava erupted at the mid ocean ridge
Stratovolcano on continent
side of subduction zone
Earth - Erosion & Surface processes
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Mass wasting
Wind -deserts
Biological (unique)
Water -main process
 River Channels erode at head, deposit at mouth
 Materials move along beaches
 Glaciers grind material down
Earth -Cratering
Earth has about 200 craters at the surface.
Earth’s Volatiles
(atmosphere and hydrosphere)
Earth is unique in that:
• the majority of it’s volatiles are liquid.
• Atmospheric composition is not all CO2
(78% N2 , 21% O2 ,<1% others, 0.003 CO2 )
• Life affects the atmospheric balance.
Earth Oceans and Temperature
Why does Earth have oceans
while Venus and Mars do not?
• Earth is the right temperature to have liquid
water due to distance from the Sun.
• Temperatures are maintained by moderate
greenhouse warming
• CO2 balance maintained by oceans and life
– (they act as a sink for all the CO2 that would
otherwise be in the atm. making extra warming)
• Magnetic field prevents H2O breakup.
Why Does Earth have a
Nitrogen/Oxygen Atmosphere?
• Most of the CO2 is locked up. Nitrogen
is the main ingredient left.
• Plant life produces oxygen, as plants
increase oxygen levels increase. Large
excess over time.
• Some of excess oxygen gets broken
and remade into ozone
– (3 O2 molecules become 2 O3)
Terrestrial Worlds 4
Our Moon
Moon basics
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Earth’s nearest neighbor , 14th largest world
Orbit -27.3 Earth days
Sidereal day -27.3 Earth days
Surface gravity -1.61 m/s2 (16% of Earth)
No global magnetic field
Only world visited by humans
Compare and contrast the 2 sides of the Moon
Near Side
Far Side
Maria make up 16% of the Moon’s surface
and almost all of them are on the Near side
Main lunar materials
• White highlands
– Anorthosite (a rock full of white feldspar)
• Dark maria
– Basalt (black from iron content)
Volcanism – Maria Formation
• fluid basalts make flood plains that fill large craters
• All occur early in lunar history, 3.8-3.2 billion yrs ago
Large impact
crater
weakens
crust
Heat build-up
allows lava to
well up to
surface
Cooled lava
is smoother
and darker
than
surroundings
Impact cratering
is dominant
process
Surface Processes
• Mass Wasting
• Radiation damage
Moon vs. Mercury
What do you think is similar about them? What is different?
• What processes shaped our Moon?
– Early cratering still present
– Maria resulted from early volcanic floods
– no shrinkage scarps
• What processes shaped Mercury?
– Cratering similar to Moon,
– some volcanism, but no large floods
– Shrinkage scarps
Moon Formation
• Early Theories: Capture, Co-formation(twin),
broken off from Earth (fission).
• Chemistry of Moon rocks show Moon is both
like and unlike Earth
• Result: Impactor Theory
– Moon formed by a giant asteroid striking a
glancing blow on the Earth
Impactor Theory
Giant impact stripped matter from Earth’s crust
Stripped matter began to orbit
Then accreted into Moon
Lunar Atmosphere
– 10-14 bars of pressure (negligible)
• Gas comes from impacts that eject surface atoms
Moon
– Temperatures 225 oF in day
-243oF at night
Why are smaller terrestrial
bodies such as Mercury or the
Moon "geologically dead"?
A. They don't have volcanoes.
B. They cooled off faster than Earth did.
C. They don't have erosion.
D. They were hit by fewer meteorites than
Earth.
Terrestrial Worlds 5
Mars
Mars basics
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4th planet from Sun (1.5 AU), 7th largest world
Orbit - 1.88 Earth years
Sidereal rotation - 25 hours
Surface gravity- 3.71 m/s2 (39% of Earth)
• Too cold for liquid water (only ice or gas)
• Spacecraft- Russian program mostly unsuccessful
- USA- Vikings 1& 2 in 1970s
- “Follow the Water” program 1990s-now
Map of Mars
Mars Polar Caps -Solid CO2
North
South
Color height map of Mars
(Red-high, Blue-low)
Mars- Volcanism
Two main types of Volcanism:
Older- fluid lavas, flood plains and flattish volcanoes
(forms the older surfaces on Mars)
Younger- large shield volcanoes
(Tharsis region and Elysium region).
– Note. The volcanoes pour out as much lava as the
Hawaiian islands, but without plate tectonics it piles
up in 1 place, making giant volcanoes.
Tharsis Bulge
Volcanic region
Olympus Mons
Largest Volcano in
the Solar System
Mars tectonics Tharsis extension faulting
Tharsis
extension
faulting
Noctis
Labyrinthus
and Valles
Marineris
Valles Marineris
3000 miles long, 7 miles deep
Mars Cratering
• Surfaces old in southern highlands
• ‘Middle aged’ in the Northern lowlands
• Largest craters are in south, from age of
Heavy Bombardment:
– Argyre basin ~1120 miles across
– Hellas ~1430 miles across
Mars Cratering - Hellas basin
Mars
Cratering
- Hellas is
over 9km
deep
Mars Surface
Processes (Dominant)
1) Wind
Fields of sand dunes
Mars Surface Processes – 2) Water
Water channels seen across the surface
Mars Surface Processes – 2) Water
Water channels seen across the surface
Opportunity at Sinus Meridiani
- A dried up lake?
Evidence of Running Water
at Sinus Meridiani
• Jarosite a mineral made in water.
• High sulfur & chlorine levels- salt pan from dried lake.
• Vugs -holes left after water dissolves away minerals.
• “Blueberries” -spheres of hematite made in water.
• Cross-bedding -rock forms made from water ripples.
The Missing Water -Underground Ice?
The Martian Atmosphere
• 0.007 bars of pressure (1/100 x Earth)
• 96% CO2 3.5% N2 < 1% others
• Temperatures13 oF in day (max. recorded 63 oF)
-135 oF at night (min. -200 oF at poles)
• Current pressure/temperature conditions
are too low for stable liquid water. Water
found as gas or ice.
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
• Traces of magnetic field only found on oldest rocks.
• Younger rocks no field.
• Mars once had magnetic field early on, but not today.
• Magnetic field may have protected early Martian
atmosphere from the solar wind.
• Solar wind may have stripped atmosphere away after
field decreased because of interior cooling.
• If much water and carbon dioxide was lost, the Martian
greenhouse effect would decrease and the temperatures
would be too low for liquid water.