Venus
Venus
Venus’s Vital Statistics
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Avg. Distance: 0.72 AU
Mass: 4.87 x 1024 kg (.82 Earth)
Radius: 6052 km (0.95 Earth)
Average Density: 5.2 g/cm3
Sidereal Period: 224.7 days (~ 0.61 year)
Axial tilt: 177.4°
Rotation period: -243.0 days
Almost no magnetic field: <0.001 (Earth=1)
Mean surface Temp: 730 K (~900º F)
Venus’s Rotation
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Prior to radar observations, controversial
25-day rotation period?
l  24-hour rotation period?
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Radar showed: 243 retrograde rotation period
Planetary “north” and “south” defined
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Convention: planets always rotate west to east
Venus’s south pole is “up”
Why is Venus upside down and backward? J
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Hit by large body early in Venus’s evolution
The Surface of Venus
Large Scale Structure
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Two highland areas - “continents”
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Ishtar Terra
Lakshmi Planum (plateau - 1500 km across at widest point)
l  Maxwell Montes ~ 14 km above deepest depressions
l  Mount Everest ~ 20 km above deepest ocean floor
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Aphrodite Terra
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Ovda Regio (western region)
Venus continents only 8% of the surface area
l  Earth continents - 25% of surface
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No sign of tectonic plate features
The Surface of Venus
Volcanism
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Lava domes
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Lava oozes out then withdraws
Shield volcanoes
Lava wells up through “hot spots”
l  Volcano builds up over time
l  Caldera (crater at summit) characteristic
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Coronae
Largest volcanic structures
l  Unique to Venus
l  Mantle upwelling
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The Surface of Venus
Cratering
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~ 1/10 that of lunar surface
Implies a young surface
l  Estimated at ~ 500 Myr old
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Theory: entire surface melts ~ every 700 Myr
l  Thick crust traps heat
l  Trapped heat causes surface to melt
The Interior of Venus
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Thought to be similar to Earth’s interior
Including partially molten iron core
l  So why basically no magnetic field?
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Slow rotation!
The Atmosphere of Venus
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Pressure 90 times Earth’s
Extends much higher troposphere up to 100 km
Sulfuric acid clouds
“jet stream” west to east
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96.5 % carbon dioxide
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~ 300 - 400 km/h
Fastest at equator
Slowest at poles
3.5 % nitrogen
Trace amounts other
Where’s the water?
RUNNAWAY GREENHOUSE
EFFECT!
Venus - Summary
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Same mass, size, and density as Earth
l  Hottest planet – surface T = 750K (900°F)
l  Pressure 90 atmospheres
l  Atmosphere ~ 96% CO2
l  Sulfuric acid clouds
l  Venera – first surface images
l  Magellan (1990) mapped in radar
l  80% surface volcanic plains