Venus and Mars
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Venus and Mars
Two most similar planets to Earth:
• Similar in size and mass
• Same part of the solar system
• Atmosphere
• Similar interior structure
Yet, no life possible on either one of them.
Venus
The Rotation of Venus
Almost all planets rotate
counterclockwise, i.e. in the
same sense as orbital motion.
Exceptions:
Venus, Uranus and Pluto
Venus rotates clockwise,
with period slightly longer
than orbital period.
Possible reason:
• Off-center collision with
massive protoplanet
The Atmosphere of Venus
UV image
Extremely inhospitable:
96 % carbon dioxide (CO2)
3.5 % nitrogen (N2)
Rest: water (H2O), hydrochloric
acid (HCl), hydrofluoric acid (HF)
4 thick cloud layers (→ surface
invisible to us from Earth).
Very stable circulation patterns with
high-speed winds (up to 240 km/h)
Given that Venus’ atmosphere consists almost
entirely of CO2, what would you expect for the
temperature on the surface of Venus?
1.
2.
3.
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Very cold because no
light reaches the surface.
Moderately warm, similar
to Earth
Very hot because of a
very efficient greenhouse
effect.
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The Atmosphere of Venus
UV image
Extremely inhospitable:
96 % carbon dioxide (CO2)
3.5 % nitrogen (N2)
Rest: water (H2O), hydrochloric
acid (HCl), hydrofluoric acid (HF)
4 thick cloud layers (→ surface
invisible to us from Earth).
Very stable circulation patterns with
high-speed winds (up to 240 km/h)
Very efficient “greenhouse”!
Extremely high surface temperature
up to 745 K (= 880 oF)
Would you expect to find many impact
craters on Venus (like on Mercury)?
1.
Yes; even more because Venus
is more massive.
Yes, just about as many as on
Mercury.
No, because there have been
much fewer meteorites than
near the orbit of Mercury.
No, because Venus is protected
from meteorite impacts by its
dense atmosphere.
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The Surface of Venus
Early radar images already revealed mountains, plains, craters.
More details from orbiting and landing spacecraft:
Venera 13
photograph of
surface of Venus:
Colors modified by
clouds in Venus’
atmosphere
After correction for
atmospheric color
effect:
Radar Map of Venus’ Surface
Surface features
shown in artificial
colors.
• Scattered impact
craters
• Volcanic regions
• Smooth lava flows
Lava Flows
Young, uneven lava flows (shown: Lava flow near
Flagstaff, AZ) show up as bright regions on radar maps.
Surface Features on Venus
Smooth lowlands
Highland regions:
Maxwell Montes are ~ 50 %
higher than Mt. Everest!
Craters on Venus
Nearly 1000 impact
craters on Venus’
surface:
→ Surface not
very old.
No water on the
surface; thick,
dense atmosphere
→ No erosion
→ Craters appear sharp
and fresh
All volcanoes on Venus are …
1. Subduction-zone
volcanoes.
2. Shield volcanoes.
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Shield Volcanoes
Found above
hot spots:
Fluid magma
chamber, from
which lava erupts
repeatedly through
surface layers
above.
All volcanoes on Venus and Mars are shield volcanoes
Volcanism on Venus
Sapas Mons (radar image)
~ 400 km (250 miles)
2 lava-filled calderas
Lava flows
Volcanic Features
on Venus
Aine Corona
Baltis Vallis: 6800 km long
lava flow channel (longest
in the solar system!)
Lava flows
Some lava flows
collapsed after molten
lava drained away
Coronae: Circular bulges formed by
volcanic activity
Pancake Domes:
Associated with
volcanic activity
forming coronae
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The collapsed lava flows on Venus are very
similar to which surface features on the Moon?
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Long rays of ejecta from
impact craters.
Lobate Scarps.
Sinous Rilles.
Maria.
Large mountain ridges.
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Lunar Highlands
and Lowlands
Sinous rilles =
remains of ancient
lava flows.
May have been lava
tubes which later
collapsed due to
meteoride
bombardment.
Apollo 15 landing site
Lakshmi Planum and
Maxwell Mountains
Radar image
Wrinkled mountain formations indicate compression and wrinkling,
though there is no evidence of plate tectonics on Venus.
Simulated flights over the surface of Venus
A History of Venus
Complicated history; still poorly understood.
Very similar to Earth in mass, size, composition, density,
but no magnetic field → Core solid?
→ Solar wind interacts
directly with the
atmosphere, forming a bow
shock and a long ion tail.
What makes soda drinks bubble?
1.
The heat in the drink evaporates
water, which rises up in bubbles.
Gases given off by the breathing of
bacteria in the drink.
Oxygen (O2) dissolved in the
water.
Sulfur dioxide (SO2) dissolved in
the water (forming Sulfurous Acid,
H2SO3).
Carbon dioxide (CO2) dissolved in
the water (forming Carbonic Acid,
H2CO3).
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A History of Venus
Complicated history; still poorly understood.
Very similar to Earth in mass, size, composition, density,
but no magnetic field → Core solid?
→ Solar wind interacts
directly with the
atmosphere, forming a bow
shock and a long ion tail.
CO2 produced during
outgassing remained in
atmosphere (on Earth:
dissolved in water).
Any water present on the
surface rapidly evaporated →
feedback through enhancement
of greenhouse effect
Mars
• Diameter ≈ ½ Earth’s diameter
• Very thin atmosphere, mostly CO2
• Rotation period = 24 h, 40 min.
• Axis tilted against orbital plane by 25o,
similar to Earth’s inclination (23.5o)
• Seasons similar to Earth → Growth
and shrinking of polar ice cap
• Crust not broken into tectonic plates
• Volcanic activity (including highest
volcano in the solar system)
The Atmosphere of Mars
Very thin: Only 1 % of
pressure on Earth’s surface
95 % CO2
Even thin Marsian
atmosphere evident
through haze and clouds
covering the planet
Occasionally: Strong dust
storms that can enshroud
the entire planet.
What is rust?
1.
2.
3.
4.
5.
Silicon dioxide (SiO2)
Hydrogen oxide (H2O)
Aluminum (Al)
Iron oxide (FeO)
Carbon dioxide (CO2)
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The Atmosphere of Mars (II)
Most of the Oxygen bound in oxides in rocks
→ Reddish color of the surface
Which of the following gasses is the heaviest?
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5.
Oxygen (O2)
Hydrogen (H2)
Helium (He)
Carbon dioxide (CO2)
Water vapor (H2O)
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History of Mars’ Atmosphere
Initial atmosphere from outgassing.
Small mass of Mars;
moderate temperatures
Lighter gasses:
Molecule velocity greater
than escape velocity: →
gasses escape into space.
Mars has lost all lighter gasses;
retained only heavier gasses (CO2).
Please press “1” to check your transmitter.
History of Mars’ Atmosphere
Initial atmosphere from outgassing.
Small mass of Mars;
moderate temperatures
Lighter gasses:
Molecule velocity greater
than escape velocity: →
gasses escape into space.
Mars has lost all lighter gasses;
retained only heavier gasses (CO2).
The Atmospheric Temperature Structures
of the Terrestrial Planets
Why would the surface of Venus be colder than
Earth’s if here was no greenhouse effect?
1.
Because of its longer day/night
cycle.
Because of Venus’ dense cloud
cover that reflects most of the
sunlight.
Because Venus is further away
from the sun than Earth.
Because of its retrograde rotation.
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Why do the atmospheres of Venus
and Mars not have the temperature
“bump” that we see in the Earth’s
stratosphere?
:10
Because Venus and Mars don’t have
an ozone layer.
Because on Venus and Mars, there’s
no greenhouse effect active.
Because X-rays are not absorbed in
the atmospheres of Venus and Mars.
Because visible light does not
penetrate the atmospheres of Venus
and Mars.
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The Geology of Mars
Giant volcanoes
Valleys
Impact craters
Reddish deserts of broken
rock, probably smashed by
meteorite impacts.
Vallis Marineris
Geology of Mars (II)
Northern Lowlands: Free of craters; probably
re-surfaced a few billion years ago.
Possibly once
filled with water.
Southern Highlands: Heavily cratered; probably
2 – 3 billion years old.
Volcanism on Mars
Volcanoes on
Mars are shield
volcanoes.
Olympus Mons:
Highest and
largest volcano
in the solar
system:
Height = 27 km!
What is the elevation of Mt. Everest?
1.
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4.
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2,512 m.
5,136 m.
8,868 m.
15,925 m.
21,856 m.
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Why are the highest volcanoes on Mars much
higher than the highest mountains on Earth?
They are better fed by Mars’
caramel interior.
Mars provides a weaker gravity
that would resist the build-up of
mountains.
There is no erosion on the
surface of Mars.
Subduction zones on Mars are
much more violent than on Earth.
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Volcanism on Mars (II)
Tharsis rise
(volcanic bulge):
Nearly as large as
the U.S.
Rises ~ 10 km above
mean radius of Mars.
Rising magma has
repeatedly broken
through crust to
form volcanoes.
Hidden Water on Mars
No liquid water on the surface:
Would evaporate due to low pressure.
But evidence for liquid water in the past:
Outflow channels from sudden,
massive floods
Collapsed structures after
withdrawal of sub-surface water
Valleys resembling
meandering river beds
Gullies, possibly from debris flows
Central channel in a valley
suggests long-term flowing water
Hidden Water on Mars (II)
Gusev Crater and Ma’adim Vallis:
Giant lakes might have drained repeatedly
through the Ma’adim Vallis into the crater.
Evidence for Water on Mars
Galle,
the “happy face crater”
Meteorite ALH84001:
Identified as ancient rock from Mars.
Large impacts may have
ejected rocks into space.
Some minerals in this meteorite were
deposited in water → Martian crust must
have been richer in water than it is today.
Ice in the Polar Cap
Polar cap contains
mostly CO2 ice,
but also water.
Multiple ice regions
separated by valleys
free of ice.
Boundaries of polar
caps reveal multiple
layers of dust, left
behind by repeated
growth and melting
of polar-cap regions.
Could you, in principle, go skiing
on the CO2 ice caps of Mars?
1.
2.
Yes. CO2 ice is just as
slippery as water ice.
No. CO2 ice is not
slippery like water ice.
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The Moons of Mars
Two small moons: Phobos
(diameter ~ 25 km) and
Deimos (diameter = 12 km).
Too small to pull themselves
into spherical shape.
Typical of small, rocky bodies:
Dark grey, low density.
Phobos
Very close to Mars; orbits around
Mars faster than Mars’ rotation.
Probably captured from outer asteroid belt.
Deimos
Since Mars’ Moons are orbiting the planet faster
than Mars’ rate of rotation, an observer on Mars will
see the moons rise in the … and set in the …!
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5.
North, South.
South, North.
East, West.
West, East.
Not at all. They will always
be up or always be down.
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