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 (CO 2 ) 3.5 % nitrogen (N 2 ) Rest: water (H 2 O), 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)

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Given that Venus’ atmosphere consists almost entirely of CO 2 , what would you expect for the temperature on the surface of Venus?

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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 (CO 2 ) 3.5 % nitrogen (N 2 ) Rest: water (H 2 O), 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 o F)

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

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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) Lava flows 2 lava-filled calderas

Volcanic Features on Venus

Aine Corona Coronae: Circular bulges formed by

Baltis Vallis: 6800 km long lava flow channel (longest in the solar system!)

Lava flows Pancake Domes: volcanic activity Some lava flows collapsed after molten lava drained away Associated with volcanic activity forming coronae

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.

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What makes soda drinks bubble?

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

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

Oxygen (O 2 ) dissolved in the water.

Sulfur dioxide (SO H 2 SO 3 ).

2 ) dissolved in the water (forming Sulfurous Acid, Carbon dioxide (CO H 2 CO 3 ).

2 ) dissolved in the water (forming Carbonic Acid,

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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.

CO 2 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 CO 2 • Rotation period = 24 h, 40 min.

• Axis tilted against orbital plane by 25 o , similar to Earth’s inclination (23.5

o ) • 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 % CO 2 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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Silicon dioxide (SiO 2 ) Hydrogen oxide (H 2 O) Aluminum (Al) Iron oxide (FeO) Carbon dioxide (CO 2 )

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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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Oxygen (O 2 ) Hydrogen (H 2 ) Helium (He) Carbon dioxide (CO 2 ) Water vapor (H 2 O)

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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 (CO 2 ).

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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 (CO 2 ).

The Atmospheric Temperature Structures of the Terrestrial Planets

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Why would the surface of Venus be colder than Earth’s if here was no greenhouse effect?

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 1.

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stratosphere?

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

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

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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.

Volcanoes on Mars are shield volcanoes.

Volcanism on Mars

Olympus Mons: Highest and largest volcano in the solar system: Height = 27 km!

What is the elevation of Mt. Everest?

1. 2,512 m.

2. 5,136 m.

3. 8,868 m.

4. 15,925 m.

5. 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” Large impacts may have ejected rocks into space.

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 CO 2 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.

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Could you, in principle, go skiing on the CO

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ice caps of Mars?

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Yes. CO 2 ice is just as slippery as water ice.

No. CO 2 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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North, South.

South, North.

East, West.

West, East.

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

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