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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.
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VenusThe Rotation of Venus
Almost all planets rotate counterclockwise on their axis,
i.e. in the same sense as orbital motion (revolution).
Exceptions: Venus, Uranus and Pluto
Venus rotates clockwise, with period slightly longer than orbital period.
Possible reason:
Off-center collision with massive protoplanet
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A History of VenusComplicated history; still poorly understood.
Very similar to Earth in mass, size, composition, density,
but no magnetic field → is the core solid?
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
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The Atmosphere of Venus
UV imageExtremely inhospitable:96 % carbon dioxide (CO2)3.5 % nitrogen (N2)
0.5%: 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)
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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).
Extremely high surface temperature up to 745 K (= 880 oF)
Very efficient “greenhouse”!
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The Surface of VenusEarly radar images have already revealed mountains, plains, and 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:
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Radar Map of Venus’ Surface
Surface features shown in artificial
colors.
• Scattered impact craters
• Volcanic regions
• Smooth lava flows
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Lava Flows
Young, uneven lava flows (shown: Lava flow near Flagstaff, AZ) show up as bright regions on radar maps.
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Surface Features on Venus
Smooth lowlands Highland regions:Maxwell Montes are ~50 %
higher than Mt. Everest!
Young, uneven lava flows show up as bright regions on radar maps.
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Lakshmi Planum and Maxwell Mountains
Radar image
Wrinkled mountain formations indicate compression and wrinkling, though there is no evidence of plate tectonics on Venus.
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Craters on Venus
Nearly 1000 impact craters on Venus’
surface:→ Surface is not very old.
No water on the surface; thick,
dense atmosphere
→ No erosion
→ Craters appear sharp and fresh
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Volcanism on Venus
Sapas Mons (radar image)
~ 400 km (250 miles) 2 lava-filled calderasLava flows
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Shield Volcanoes (Review)
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
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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
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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
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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
(salty/briny water!!!)• Crust not broken into tectonic
plates• Volcanic activity (including highest
volcano in the solar system)
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The Atmosphere of Mars
Very thin: Only 1 % of pressure on Earth’s surface
95 % CO2
Even thin Martian atmosphere evident
through haze and clouds covering the planet
Occasionally: Strong dust storms that can enshroud
the entire planet.
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The Atmosphere of Mars (II)Most of the Oxygen bound in oxides in rocks
→ Reddish color of the surface
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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).
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The Atmospheric Temperature Structures of the Terrestrial Planets
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The Geology of Mars- Giant volcanoes
- Valleys
Vallis Marineris
- Impact craters
Reddish deserts of broken rock, probably smashed by
meteorite impacts.
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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.
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Volcanism on Mars (I)
Volcanoes on Mars are shield
volcanoes.
Olympus Mons:Highest and
largest volcano in the solar
system:
Height = 27 km!
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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.
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Hidden Water on Mars (I)No liquid water on the surface because it would evaporate due to low pressure.
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
But wait! What did NASA just reveal?
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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.
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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.
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Ice in the Polar CapPolar 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.
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Mars RoversTweets from Curiosity Rover:
https://twitter.com/MarsCuriosity?ref_src=twsrc%5Egoogle%7Ctwcamp%5Eserp%7Ctwgr%5Eauthor
Spirit and Opportunity Exploration Rovers: Geology, Water
http://mars.nasa.gov/mer/home/
Curiosity Rover: Habitability
http://mars.nasa.gov/msl/mission/overview/
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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.