Venus and Mars

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Venus and Mars

Two most similar planets to Earth:

• Similar in size and mass • Atmosphere

• Similar interior structure• Same part of the solar system

Yet, no life possible on either one of them.

Venus

The Rotation of VenusAlmost 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?

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1. Very cold because no light reaches the surface.

2. Moderately warm, similar to Earth

3. 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)

Extremely high surface temperature up to 745 K (= 880 oF)

Very efficient “greenhouse”!

Would you expect to find many impact craters on Venus (like on Mercury)?

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1. Yes; even more because Venus is more massive.

2. Yes, just about as many as on Mercury.

3. No, because there have been much fewer meteorites than near the orbit of Mercury.

4. No, because Venus is protected from meteorite impacts by its dense atmosphere.

The Surface of VenusEarly radar images already revealed mountains, plains, craters.

Venera 13 photograph of

surface of Venus:

Colors modified by clouds in Venus’

atmosphere

More details from orbiting and landing spacecraft:

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 …

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1. Subduction-zone volcanoes.

2. Shield volcanoes.

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 calderasLava flows

Volcanic Features on Venus

Baltis Vallis: 6800 km long lava flow channel (longest

in the solar system!)

Coronae: Circular bulges formed by volcanic activity

Aine Corona

Lava flowsPancake Domes:

Associated with volcanic activity forming coronae

Some lava flows collapsed after

molten lava drained away

The collapsed lava flows on Venus are very similar to which surface features on the Moon?

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1. Long rays of ejecta from impact craters.

2. Lobate Scarps.

3. Sinous Rilles.

4. Maria.

5. Large mountain ridges.

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 VenusComplicated 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?

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1. The heat in the drink evaporates water, which rises up in bubbles.

2. Gases given off by the breathing of bacteria in the drink.

3. Oxygen (O2) dissolved in the water.

4. Sulfur dioxide (SO2) dissolved in the water (forming Sulfurous Acid, H2SO3).

5. Carbon dioxide (CO2) dissolved in the water (forming Carbonic Acid, H2CO3).

A History of VenusComplicated 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?

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1. Silicon dioxide (SiO2)

2. Hydrogen oxide (H2O)

3. Aluminum (Al)

4. Iron oxide (FeO)

5. Carbon dioxide (CO2)

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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1. Oxygen (O2)

2. Hydrogen (H2)

3. Helium (He)

4. Carbon dioxide (CO2)

5. Water vapor (H2O)

History of Mars’ AtmosphereInitial 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).

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History of Mars’ AtmosphereInitial 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?

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1. Because of its longer day/night cycle.

2. Because of Venus’ dense cloud cover that reflects most of the sunlight.

3. Because Venus is further away from the sun than Earth.

4. Because of its retrograde rotation.

Why do the atmospheres of Venus and Mars not have the temperature “bump” that we see in the Earth’s

stratosphere?

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1. Because Venus and Mars don’t have an ozone layer.

2. Because on Venus and Mars, there’s no greenhouse effect active.

3. Because X-rays are not absorbed in the atmospheres of Venus and Mars.

4. Because visible light does not penetrate the atmospheres of Venus and Mars.

The Geology of MarsGiant volcanoes

Valleys

Vallis Marineris

Impact craters

Reddish deserts of broken rock, probably smashed by

meteorite impacts.

Geology of Mars (II)Northern Lowlands: Free of craters; probably

re-surfaced a few billion years ago.

Southern Highlands: Heavily cratered; probably 2 – 3 billion years old.

Possibly once filled with water.

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?

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1. 2,512 m.

2. 5,136 m.

3. 8,868 m.

4. 15,925 m.

5. 21,856 m.

Why are the highest volcanoes on Mars much higher than the highest mountains on Earth?

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1. They are better fed by Mars’ caramel interior.

2. Mars provides a weaker gravity that would resist the build-up of mountains.

3. There is no erosion on the surface of Mars.

4. Subduction zones on Mars are much more violent than on Earth.

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 MarsNo 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

Large impacts may have ejected rocks into space.

Galle,

the “happy face crater” Meteorite ALH84001:

Identified as ancient rock from Mars.

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?

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1. Yes. CO2 ice is just as slippery as water ice.

2. No. CO2 ice is not slippery like water ice.

The Moons of Mars

Phobos

Deimos

Two small moons: Phobos (diameter ~ 25 km) and

Deimos (diameter = 12 km).

Too small to pull themselves into spherical shape.

Very close to Mars; orbits around Mars faster than Mars’ rotation.

Typical of small, rocky bodies: Dark grey, low density.

Probably captured from outer asteroid belt.

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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1. North, South.

2. South, North.

3. East, West.

4. West, East.

5. Not at all. They will always be up or always be down.