Venus

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Venus
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Ground-based Images of Venus
Inferior Conjunction
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Photograph of Venus by the Pioneer
Venus Orbiter.
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Hubble UV Image
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Basic facts about Venus
Semi-major axis 0.72 A.U. Equatorial radius
0.95R? Mass 0.85M? Rotation Period 243 solar
days (retrograde!) No moons.
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Practically nothing was known about the
surface conditions or even the rotation rate of
Venus until the 1950s. The rotation was first
deduced from radar in the 1960s. The rotation of
Venus is very slow (243.01days) and is
retrograde! This implies the Venusian day is
116.8 Earth days.
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The Rotation of Venus is Retrograde with a period
of 243.01 days. This means that the Venusian day
is 116.8 Earth days, exactly 1/5th the Synodic
period of Venus!!
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The temperature on Venus was first measured by
detecting Blackbody radiation (radio waves) from
Venus. Average temperature 750K 480C 900F!
This high temperature is due to the Greenhouse
effect
Atmospheric Composition of Venus N2 3 O2
0 CO2 97 Other 0
The atmospheric pressure on Venus is 90 Earth
atmospheres
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The thick atmosphere, lack of water, and high
abundance of CO2 means that Venus experiences a
Run-Away Greenhouse Effect, which raises its
surface temperature to 750K 480 C 900 F.
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Why does Venus experience a runaway
greenhouse effect and not the Earth?
Because the Earths atmosphere also contains
water, which produce clouds
Because Venus is much closer to the sun
Because Venus has lots of volcanoes
Because of the lack of polar ice caps

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Venera 13 images taken from the surface of Venus
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The Geology of Venus

• The Magellan spacecraft orbited Venus from 1990
  to
• During this time, it mapped 99 of the surface
• of Venus by radar.

These maps showed many volcanic structures,
including very large volcanoes, plus a surface
with an apparently uniform age of about 500
million years.
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Global Radar image of Venus taken by the Magellan
spacecraft
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Magellan Topographic Map of Venus

• Note the absence of clearly defined continental
  plates.
• Venus does not have plate tectonics (continental
• drift).

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Lack of continental drift on Venus is probably
due to its very hot temperature complete lack
of water in its crust. Under such conditions,
the crust and mantle of Venus is much stiffer
than the Earths, making impossible the flow
necessary for continental drift.
This has apparently led to a thick lithosphere
on Venus rather than the rather thin crust of the
Earth.
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Sif Mons volcano
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Three volcanoes on Venus
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More Volcanic Structures on Venus
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Beta Regio Volcanic Structures
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Craters on Venus
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Distribution of Impact craters on Venus
The even distribution of craters on Venus
suggests a uniform age for the entire surface,
unlike Earth. This further suggests that geology
on Venus is episodic and is composed of epochs
of catastrophic resurfacing followed by
long periods of quiescence.
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Venus landscape
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Magnetic Field
Venus does not have a detectable magnetic field.
Why?
It probably has a molten iron core like the Earth
but
Its slow rotation means that the dynamo effect is
not operational.
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Atmospheric Structure of Venus