Transcript A105 Stars and Galaxies

A100 - Comparing
Terrestrial
Planets
Next: Chapter 9 – Outer Planets
Quiz 7 today
Rooftop on Nov. 10, Kirkwood Nov. 12
Homework due TODAY
Today’s APOD
The Sun Today
The Martian
Interior
 Differentiated like the Earth’s interior into a crust,
mantle, and iron core
 Having a mass between that of dead Mercury and
lively Earth/Venus implies Mars should be
intermediate in tectonic activity
 Numerous volcanic peaks and uplifted highlands exist
 Olympus Mons and other volcanoes do not show any craters
on their slopes indicating they may still occasionally erupt
Surveying
the Red
Planet
Mars Topography
Why are the northern and southern
hemispheres of Mars so different?
North
• smooth surface
• few craters
• lower elevation
• ***younger***
South
• rough surface
• heavily cratered
• higher elevation
• ***older***
Surveying
the Red
Planet
1.
Hypotheses
Did a major impact (or several
large impacts) resurface the
northern hemisphere?
NO - Not circular, no rim…
2. Did an ancient ocean in the northern hemisphere
eroded away the surface, erasing the craters?
NO - No shoreline, slopes not consistent, features at
boundary suggest compression
Surveying
the Red
Planet
Plate Tectonics on Mars?
New crust spreads
and is “subducted”
where convection in
the mantle pulls it
down
Compression features
will form where new
crust encounters old
crust
Rising material from the
interior creates a “rift” and
forms new crust
Subduction provides fuel for volcanic
activity (Tharsis volcanoes?)
Largest Mountain in the Solar System
Surveying
the Red
Planet
More evidence for plate
tectonics?
The crust of
mars is
thinner in the
northern
hemisphere
S
N
Plate tectonics cools the
interior; when the interior cools
off, mantle convection ends, and
plate tectonics stop.
When a rift expands
quickly, new crust is
smooth and thin
Surveying
the Red
Planet
Magnetic
Stripes
• Surface magnetic field
measured by MGS
• Bands of opposite N/S
polarity
• Mars once had a reversing magnetic field – a core
dynamo like Earth’s
• Evidence of mantle convection and plate tectonics
• Dynamo ended about 4 billion years ago, before the
interior cooled
Surveying
the Red
Planet
Mars Topography
• A mixture of old and
“really old” terrain
• Evidence suggests
that plate tectonics
resurfaced the
northern hemisphere
early in martian
history
Linear shape of Valles Marineris
suggests it was a rift formed through
plate tectonics
The Atmosphere of Mars
 Clouds and wind blown
dust are visible evidence
that Mars has an
atmosphere
 Spectra show the
atmosphere is mainly CO2
(95%) with traces of N2
(3%), oxygen and water
 The atmosphere’s density
is about 1% that of the
Earth’s
Not a drop of rain…
No rain falls,
despite clouds
Atmosphere is too
cold and dry
Fog seen in valleys
and ground frost has
been observed
CO2 “snow” falls on
poles during winter
Ancient Atmosphere of Mars
 Dry river beds indicate
liquid water flowed in Mars’s
past
 This implies that Mars had
to have a denser atmosphere
(higher pressure) to prevent
the fast vaporization of
surface water into the
atmosphere
 Cratering indicates that this
thicker atmosphere
disappeared about 3 billion
years ago
Surveying
the Red
Planet
Climate Change on Mars?
Percival Lowell first
popularized the idea that
early Mars was warm and wet
Past?
Wet and Warm?
Modern
Cold and Arid
Surveying
the Red
Planet
Evidence for
Water Ice on Mars
Polar caps
Ground ice (Mars
Odyssey)
Surface
frost,
Viking 2
Surveying
the Red
Planet
Headscarp of Chasma Boreale
1000 m of layered ice, frozen sand dunes, and
layered sedimentary rock above a cratered basement
Surveying
the Red
Planet
Evidence for
Flowing Water
in the Past
Viking orbiter
found channels
Martian delta
Fossil delta on Earth
Surveying
the Red
Planet
Two Causes of
Climate Change
• Orbital and axial variations
• Long-term evolution
Mars is closer to the sun during its
southern summer and further from
the sun during the northern summer.
The southern summer is shorter and
hotter, while the northern summer is
longer and cooler.
The difference affects polar ice loss,
weather patterns, and dust storms.
Surveying
the Red
Planet
The Martian Atmosphere –
Standard Model
• Large CO2 abundance up to ~ 3.8 Gyr
allows warm climate and channels
• ~ 3.8 Gyr: Heavy bombardment removes
much of early atmosphere
• Further loss of CO2 to carbonate
minerals and escape gradually reduces
CO2 to present levels But – some problems with
this model (nitrogen
abundance doesn’t match,
not enough carbonates on
Martian surface)
Surveying
the Red
Planet
Alternate
Models
• Transient warmings?
– large impacts
– thermal events, volcanoes
W. K. Hartmann
• Water features caused by other fluids?
• Pyroclastic flows
• Sulfur-rich fluid lavas
Comparing
the
Terrestrial
Planets
?
Role of Mass and Radius
 Mass and radius affect interior temperature
 This in turn determines the level of tectonic activity
 Low-mass, small-radius planets will be cooler inside and
hence less active than larger planets
 This relationship is in fact observed with Mercury (the
least active), then Mars, then Venus/Earth
The Role of
Sunlight
 Warming from sunlight depends on the planet’s
distance from the Sun – the closer the warmer
 Warming also depends on the amount and makeup of
the atmosphere
 Solar warming and atmospheric chemistry also
determines the structure of the atmosphere, which
may affect the amount of warming
 On warmer Venus lifts water vapor to great heights in its
atmosphere
 On cooler Earth, water condenses out at lower heights and the
upper atmosphere is almost totally devoid of water
The Role of Biological Processes
Biological processes remove CO2 from the
atmosphere
Sea creatures use dissolved CO2 in ocean water
to make shells of calcium carbonate
Shells fall form sediment on the ocean bottom
Sediment becomes rock, sequesting CO2
With CO2 removed, mostly N2 is left
CO2 is recycled back into the atmosphere by
tectonic activity
Green plants break down H2O, C02 during
photosynthesis, producing oxygen
Comparing Planets
 Earth
 Mercury
 Low mass
 No atmosphere
 No plate tectonics
 Old crust
 No life
 Venus
Massive
Extensive
atmosphere
Active vulcanism?
New crust
No plate tectonics
No Life
 Massive
 Modest atmosphere
 Some vulcanism
 Plate tectonics
 New crust
 Life
 Mars
 Medium Mass
 Thin CO2 atmosphere
 Some vulcanism
 Early plate tectonics?
 Old and not-so-old crust
 Life?
ASSIGNMENTS
this week
 Next Week – Ch 9 – Outer Planets
 Rooftop session on Nov. 10
 Kirkwood Open Nov. 12
 Turn in homework!