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Chapter 9
Venus
© 2014 Pearson Education, Inc.
9.1 Orbital Properties
• Venus is much brighter than Mercury, and can be farther
from the Sun
• Called morning or evening star, as it is still “tied” to Sun
• Brightest object in the sky, after Sun and Moon
© 2014 Pearson Education, Inc.
9.1 Orbital Properties
Apparent brightness of Venus varies, due to changes in
phase and distance from Earth
Venus appears
brightest when it
is about 39o from
the Sun
© 2014 Pearson Education, Inc.
9.2 Physical Properties
• Radius: 6000 km (.95 x Earth)
• Mass: 4.9 x 1024 kg
• Density: 5200 kg/m3 (5.2 g/cm3)
• Rotation period: 243 days, retrograde (CW rotation)
• Atmosphere
is 90x Earth’s
(14.92 psi x
90 = 1342.8
psi).
• Composition
and layering
is similar to
Earth’s
© 2014 Pearson Education, Inc.
9.2 Physical Properties
Slow, retrograde rotation of Venus results in large difference
between solar day (117 Earth days) and sidereal day (243
Earth days); note that the solar day is a large fraction of the
year, and the sidereal day is even longer than the year (225
Earth days).
© 2014 Pearson Education, Inc.
9.3 Long-Distance Observations
of Venus
Dense atmosphere and thick
clouds make surface
impossible to see
Surface temperature is about
730 K—hotter than Mercury!
© 2014 Pearson Education, Inc.
9.3 Long-Distance Observations
of Venus
Even probes flying near
Venus, using ultraviolet or
infrared, can see only a little
deeper into the clouds
Longer infrared wavelength
allows us to “see” deeper
into Venus’s lower clouds
© 2014 Pearson Education, Inc.
9.4 The Surface of Venus
Surface is relatively smooth
Two continent-like features: Ishtar Terra and Aphrodite
Terra
No large scale plate tectonics
Mountains, a few craters, many volcanoes and large lava
flows
© 2014 Pearson Education, Inc.
9.4 The Surface of Venus
Surface mosaics of Venus (Ishtar Terra is upper left,
Aphrodite is lower right)
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9.4 The Surface of Venus
Surface maps of Venus, with Earth comparison
Elevated areas - 8% of Venus, 25% of Earth
© 2014 Pearson Education, Inc.
9.4 The Surface of Venus
Ishtar Terra is one of two continent-sized features on the
surface of Venus. Maxwell Montes mountain range is 14
km above lowest elevation. (Mt. Everest is 20 km above
deepest trench)
Right: Cleopatra impact crater with center lava flow and
double-ringed structure indicating an impact crater
© 2014 Pearson Education, Inc.
9.4 The Surface of Venus
The other is Aphrodite Terra
The intersecting ridge indicate repeated compression and
buckling of the surface. Dark areas are extensive lava
flows.
© 2014 Pearson Education, Inc.
9.4 The Surface of Venus
Lava has flowed from cracks or fissures on the surface
(these are 50 km long). Upwelling magma flowed, solidified,
then material withdrew from below, and surface collapsed.
Some rilles (lava channels) are long and have deltas.
© 2014 Pearson Education, Inc.
9.4 The Surface of Venus
Volcanoes on Venus; most are shield volcanoes. (Sif Mons
(left), and Gula Mons (right)) Similar to the Hawaiian Islands
(basalt), but are distributed randomly – unlike Earth’s
volcanoes located at plate boundaries. They are big because
there is no movement of plates over an active vent.
© 2014 Pearson Education, Inc.
9.4 The Surface of Venus
Other volcanic features include lava domes (pancake domes
25 km across) and coronas. Coronae are unique to Venus.
They are caused by upwelling mantle material (300 km
across).
Evidence that volcanism is still going on include: CO2 levels
fluctuate, bursts of radio energy (lightning from volcanism).
No “smoking gun” or erupting volcano has been seen.
© 2014 Pearson Education, Inc.
9.4 The Surface of Venus
Impact craters on Venus, the largest named after Margaret
Mead (Mead Crater - 280 km). Erosional agents include
volcanism and a little from the atmosphere. Much of the planet
resurfaces every 500 my. Young crust – less than 1 BY, some
200 to 300 my old.
© 2014 Pearson Education, Inc.
9.5 The Atmosphere of Venus
Venus’s atmosphere is
very dense
Solid cloud bank 50–70
km above surface
Atmosphere is mostly
carbon dioxide; clouds
are sulfuric acid
© 2014 Pearson Education, Inc.
9.5 The Atmosphere of Venus
Upper atmosphere of Venus has high winds, but
atmosphere near surface is almost calm
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9.5 The Atmosphere of Venus
Venus is the victim of a runaway greenhouse effect—just kept
getting hotter and hotter as infrared radiation was reabsorbed
© 2014 Pearson Education, Inc.
9.6 Venus’s Magnetic Field and
Internal Structure
No magnetic field, probably because rotation
is so slow
No evidence for plate tectonics
Venus resembles a young Earth (1 billion
years)—no asthenosphere, thin crust
© 2014 Pearson Education, Inc.