Lesson 5
Venus
Venus from Earth
At its brightest, Venus is
about 60 times brighter
than the brightest stars.
Venus is the morning or evening
“star”
• Venus is never more than 47 degrees from the
Sun.
Why does Venus look this way?
1. The Earth is casting a
shadow on Venus
2. Mercury is casting a
shadow on Venus
3. We are seeing the day
and night side of Venus
4. There are clouds
blocking part of Venus
.
25%
1
25%
25%
2
3
25%
4
Venus phases
• What is Venus’s phase when it is closest
to the Earth?
.
1. New Venus
2. Full Venus
3. Half-lit
33%
1
33%
2
33%
3
When Venus is close to the Earth we only
see the night side of Venus. When it is on
the other side of the Sun we see the full
Venus
• Galileo was the first to see the phases of
Venus, using a small telescope. (1610)
• The changing size and phases was proof that
Venus didn’t orbit the Earth. Instead, Venus
had to orbit the Sun.
Venus – Basic Properties
Venus – Basic Properties
•
•
•
•
•
•
•
Diameter is 650 km less than Earth’s
Mass is 81.5% of Earth’s
Virtually a twin to Earth in size and mass.
Venus has no moon
Venus atmosphere is 90 times that of Earth
Surface temperature is ~ 870o F everywhere.
Always under cloud cover
• Venus rotates on its axis very slowly (225 Earth
Days) and in the opposite direction of that of
the other planets.
• On Venus the Sun would rise in the west and
set in the East.
• On Venus, a year is 1.92 Venus days long. So if
you were on Venus you would have about 2
days each year.
• The slow rotation and small differences in
surface temperature around the planet means
wind speeds are very slow on Venus. Virtually
no wind erosion as on Mars.
• We saw on Mars that there has been a great
deal of wind erosion.
• Venus has virtually one global temperature
with only small variations.
• Would you expect Venus to also have lots of
wind erosion on its surface?
.
1. Yes. Venus has a thick atmosphere and
is very hot. This should cause enormous
33%
33%
winds
2. Yes. Since Venus rotates slowly winds
should be able to blow from the poles
to the equator
3. No. There are no temperature
differences so wind will not develop.
1
2
33%
3
• Venus rotates on its axis very slowly and in the
opposite direction of that of the other planets.
• On Venus the Sun would rise in the west and
set in the East.
• On Venus, a year is 1.92 Venus days long. So if
you were on Venus you would have about 2
days each year.
• The slow rotation and small differences in
surface temperature around the planet
means wind speeds are very slow on Venus.
Virtually no wind erosion as on Mars.
Venus from outer space
• Venus is always shrouded in thick clouds. The
atmosphere is almost completely carbon
dioxide (CO2).
• The cloud decks seen from space are
composed mostly of sulfur dioxide (SO2).
• There is virtually no water in the atmosphere
of Venus.
Topographical Map
Red highest elevation, blue lowest
Earth topographical map
Earth Active Volcanoes
Venus volcanoes
Is there plate tectonics occurring on Venus?
Is there plate tectonics occurring
on Venus?
1. Yes
2. No
50%
1
50%
2
What type of volcanoes do you expect?
What type of volcanoes are on
Venus?
1. Strato-volcanoes
2. Shield volcanoes
3. A mixture of the
two.
33%
1
33%
2
33%
3
Venus volcanoes
Maat Mons
Gula Mons
All Venus volcanoes are shield.
• Large shield volcanoes
• Pancake Domes (smaller, sometimes form
along fissures)
• Corona (uplifts in crust causing tectonic
features)
• Arachnoids (spider-like volcanoes that have
sunk back into the surface)
Large shield volcano
Lava Flow
and
channels
Mylitta Fluctus
Lava Flow and channels
Atla Regio about 1000 km long
Helen Planitia
Long lava flow
channels (~1200 km
long) which show
signs of being
covered by later lava
flow.
Pancake volcanoes forming in a line
along fissure
Flat top, pancake domes suggest that the lava
was of higher viscosity
• If pancake domes form along crustal fissures,
why might they have higher viscosity?
.
50% that
1. There must be a subduction zone
mixes crustal material into the mantle
magma.
2. Mantle magma emerging up through
the fissure probably melts the crust
which makes the magma of higher
viscosity
1
50%
2
Corona
features
Caused by
hot mantle
material
uplifting
and sinking
over and
over again.
Arachnid volcanoes are probably volcanic domes
which sunk back down when magma retreated
About 1000 impact craters on Venus
Impact craters
• On Venus there are no impact craters smaller
than 3 km. Most are around 10 km or bigger.
• Why do you think this is?
.
1. All the smaller craters are
destroyed by geologic activity33%
2. Smaller meteors can’t make it
through the thick Venus
atmosphere
3. Venus only gets hit by big
objects.
1
33%
2
33%
3
Distribution of Impact craters
Impact craters
• On Venus there are no impact craters smaller
than 3 km. Most are around 10 km or bigger.
This is due to the protection of the extremely
thick atmosphere.
• The impact craters are randomly distributed
across the surface of Venus.
• Density is about 1.9 craters/million km2. This
is the same everywhere on the surface.
• What does this suggest?
.
1. The surface of Venus is the
33%
same age globally.
2. Younger regions on the
surface have been hit more
frequently in the recent past.
3. Venus is similar to the
highlands of the Moon
1
33%
2
33%
3
Lunar Site
Fra Mauro
Cayley
Apollo 11
Apollo 15
Apollo 12
Copernicus crater rim
Crater Density
Age
(10km/1 million km2)
550
(billions of years)
3.94
430
120
97
3.77
3.55
3.40
70
20
3.28
0.90
Impact craters
• On Venus there are no impact craters smaller
than 3 km. Most are around 10 km or bigger.
This is due to the protection of the extremely
thick atmosphere.
• The impact craters are randomly distributed
across the surface of Venus.
• Density is about 1.9 craters/million km2
• Lunar density for a 0.9 billion years old surface
is 20 craters/million km2
Piecing the evidence together.
• Few impact craters that are randomly
distributed.
• No plate tectonics.
• Volcanoes are randomly distributed across the
surface.
• What does this suggest about the surface of
Venus?
.
1. There is a combination of very old
surfaces and very young surfaces on
33%
33%
Venus
2. Craters near volcanoes are destroyed
while other places retain their ancient
craters
3. Venus must have eruptions on a
global scale that resurfaces the entire
planet.
1
2
33%
3
Piecing the evidence together.
• Few impact craters that are randomly
distributed. (Means the global surface of
Venus is about the same age).
• No plate tectonics. (Means pressure release
has to come in the form of magma plumes)
• Volcanoes are randomly distributed across the
surface. (Means that eruptions are not just in
local regions like on Mars)
Geology on Venus
• Venus appears to resurface nearly the entire
planet at the “same” time, about 200 – 600
million years ago. (Possibly over a 100 million
year period)
• Since there is no plate tectonics, pressure and
temperature builds inside of Venus and is
finally released globally, resurfacing the entire
planet.
• Activity then slows until pressure rebuilds.
• This is likely a cyclic process.