1. Venus!

2. Thought Question
What is the main reason why Venus is hotter than Earth?
Venus is closer to the Sun than Earth.
Venus is more reflective than Earth.
Venus is less reflective than Earth.
The greenhouse effect is much stronger on Venus than on Earth.
Human activity has led to declining temperatures on Earth.

3. Venus in UV light FIGURE 7-10 Venus Venus’s thick cloud cover
efficiently traps heat from the Sun, resulting in a
surface temperature even hotter than that on
Mercury. Unlike Earth’s clouds, which are made of water
droplets, Venus’s clouds are very dry and contain droplets of
concentrated sulfuric acid. This ultraviolet image was taken by
the Pioneer Venus Orbiter in (NASA)

4. Venus mapped with Radar
FIGURE 7-16 A “Global” View of Venus
A computer using numerous
Magellan images creates a simulated
globe. Color is used to enhance small-scale structures.
Extensive lava flows and lava plains cover about 80% of
Venus’s relatively flat surface. The bright band running
almost east-west is the continent-like highland region
Aphrodite Terra. (NASA)

5. Lots of volcanic features…
The surface of Venus
FIGURE 7-15 A Map of Venus
This false-color radar map of Venus, analogous to
a topographic map of Earth, shows the
large-scale surface features of the planet.
The equator extends horizontally
across the middle of the map. Color
indicates elevation—red for highest, followed
by orange, yellow, green, and
blue for lowest. The planet’s highest
mountain is Maxwell Montes on Ishtar
Terra. Scorpion-shaped Aphrodite Terra,
a continent-like highland, contains several
spectacular volcanoes. Do not confuse
the blue and green for oceans and
land. (Peter Ford/MIT, NASA/JPL)
Lots of volcanic features…

6. Venera Probes from 1970’s survived for minutes…
Venus’ surface
Venera Probes from 1970’s survived for minutes…
FIGURE 7-13 The Venusian Surface
(a) This color photograph,
taken by a Soviet spacecraft, shows rocks that
appear orange because the light was filtered through the
thick, sulfur-rich clouds. (b) By comparing the apparent color
of the spacecraft to the color it was known to be, computers
can correct for the sulfurous light. The actual color of the
rocks is gray. In this view, the rocky plates that cover the
ground may be fractured segments of a thin layer of lava.
The toothed wheel in each image is part of the landing
mechanism that keeps the spherical spacecraft from rolling.
(a: Courtesy of C. M. Pieters and the USSR Academy of Sciences;
b and c: Don Mitchell)

7. Venus’ surface Venus as we might “see” it…
FIGURE 7-13 The Venusian Surface
(a) This color photograph,
taken by a Soviet spacecraft, shows rocks that
appear orange because the light was filtered through the
thick, sulfur-rich clouds. (b) By comparing the apparent color
of the spacecraft to the color it was known to be, computers
can correct for the sulfurous light. The actual color of the
rocks is gray. In this view, the rocky plates that cover the
ground may be fractured segments of a thin layer of lava.
The toothed wheel in each image is part of the landing
mechanism that keeps the spherical spacecraft from rolling.
(a: Courtesy of C. M. Pieters and the USSR Academy of Sciences;
b and c: Don Mitchell)
… if we could stand the heat, pressure, & sulfuric acid rain!

8. FIGURE 7-13 The Venusian Surface
(c) By correcting for the curvature of this image and a similar
one taken with the camera flipped upside down, the actual
surface of Venus near the Venera Lander can be shown.
(a: Courtesy of C. M. Pieters and the USSR Academy of Sciences;
b and c: Don Mitchell)

9. FIGURE 7-14 A Venusian Landscape
A computer combined radio images to yield this perspective
view of Venus as you would see it from an altitude of
4 km (2.5 mi). The color results from light being filtered through
Venus’s thick clouds. The brighter color of the extensive lava
flows indicates that they reflect radio waves more strongly. The
vertical scale has been exaggerated 10 times to show the gentle
slopes of Sapas Mons and Maat Mons, volcanoes named for
ancient Phoenician and Egyptian goddesses, respectively.
(NASA, JPL Multimission Image Processing Laboratory)

10. FIGURE 7-17 Craters on Venus
These three impact craters, with extensive ejecta surrounding
each, are located on Venus’s southern hemisphere.
From left to right, these are craters Danilova, Howe,
and Aglaonice—all imaged using radar by the Magellan
spacecraft. The colors are based on the Venera images (see
Figure 7-13). (NASA/Magellan Images [JPL])

11. Does Venus still have active plate tectonics?
NASA’s Magellan mapped for ~ 4 years
Did not appear to have active volcanoes or plate tectonics
Based on cratering evidence, entire surface seems “repaved” 750 million years ago.

12. Venus’ Atmosphere What is it made of? How does it change in height?
How does it circulate?
FIGURE 7-13 The Venusian Surface
(a) This color photograph,
taken by a Soviet spacecraft, shows rocks that
appear orange because the light was filtered through the
thick, sulfur-rich clouds. (b) By comparing the apparent color
of the spacecraft to the color it was known to be, computers
can correct for the sulfurous light. The actual color of the
rocks is gray. In this view, the rocky plates that cover the
ground may be fractured segments of a thin layer of lava.
The toothed wheel in each image is part of the landing
mechanism that keeps the spherical spacecraft from rolling.
(a: Courtesy of C. M. Pieters and the USSR Academy of Sciences;
b and c: Don Mitchell)

13. Atmosphere of Venus
High altitude reflective clouds contain droplets of sulfuric acid (H2SO4)
Upper atmosphere has fast winds that remain unexplained.

14. Atmosphere of Venus Thick CO2 (carbon dioxide) atmosphere
Surface pressure 90 times that of Earth.
> 1300 lbs/sq. in.!

15. Greenhouse Effect on Venus
Thick carbon dioxide atmosphere produces an extremely strong Greenhouse Effect.
Earth escapes this fate - most of its carbon and water are in rocks & oceans.

16. Why is Venus so hot?
The greenhouse effect on Venus keeps its surface temperature at 470°C (950°F)
But why is the greenhouse effect on Venus so much stronger than on Earth?

17. FIGURE 7-12 The Greenhouse Effect
A portion of the sunlight
penetrates through the clouds and atmosphere of Venus, heating
its surface. The surface in turn emits infrared radiation,
much of which is absorbed by carbon dioxide (and to a much
lesser degree, water vapor). The trapped radiation helps
increase the average temperatures of the surface and atmosphere.
Some infrared radiation does penetrate the atmosphere
and leaks into space. In a state of equilibrium, the rate at which
the planet loses energy to space in this way is equal to the rate
at which it absorbs energy from the Sun.

18. Explaining Venus’ Atmosphere
Lots of Volcanoes
CO2, H2S04 are outgassed
CO2 traps infrared heat
Atmosphere heats up
Water can’t condense =>
No Rain!
No “flushing” of CO2
FIGURE 7-13 The Venusian Surface
(a) This color photograph,
taken by a Soviet spacecraft, shows rocks that
appear orange because the light was filtered through the
thick, sulfur-rich clouds. (b) By comparing the apparent color
of the spacecraft to the color it was known to be, computers
can correct for the sulfurous light. The actual color of the
rocks is gray. In this view, the rocky plates that cover the
ground may be fractured segments of a thin layer of lava.
The toothed wheel in each image is part of the landing
mechanism that keeps the spherical spacecraft from rolling.
(a: Courtesy of C. M. Pieters and the USSR Academy of Sciences;
b and c: Don Mitchell)

19. Runaway Greenhouse Effect
More evaporation, stronger greenhouse effect
Greater heat, more evaporation
The runaway greenhouse effect would account for why Venus has so little water.

20. FIGURE 7-11 Temperature and Pressure in the Venusian Atmosphere
The pressure at the Venusian surface is a crushing
90 atm (1296 lb/in2). Above the surface, atmospheric
pressure decreases smoothly with increasing altitude. The
temperature of Venus’s atmosphere increases smoothly from a
minimum of about 173 K (150°F) at an altitude of 100 km
to a maximum of nearly 750 K (900°F) on the ground.
(NASA/Magellan Images [JPL])

21. Sun’s UV light disassociates H20 at this height!
FIGURE 7-11 Temperature and Pressure in the Venusian Atmosphere
The pressure at the Venusian surface is a crushing
90 atm (1296 lb/in2). Above the surface, atmospheric
pressure decreases smoothly with increasing altitude. The
temperature of Venus’s atmosphere increases smoothly from a
minimum of about 173 K (150°F) at an altitude of 100 km
to a maximum of nearly 750 K (900°F) on the ground.
(NASA/Magellan Images [JPL])
Water condenses into clouds, allowing for rain around 0 C

22. Thought Question
What is the main reason why Venus is hotter than Earth?
Venus is closer to the Sun than Earth.
Venus is more reflective than Earth.
Venus is less reflective than Earth.
The greenhouse effect is much stronger on Venus than on Earth.
Human activity has led to declining temperatures on Earth.

23. Thought Question
What is the main reason why Venus is hotter than Earth?
Venus is closer to the Sun than Earth.
Venus is more reflective than Earth.
Venus is less reflective than Earth.
The greenhouse effect is much stronger on Venus than on Earth.
Human activity has led to declining temperatures on Earth.

24. Carbon Dioxide Cycle
“Recycle” CO2 from atmosphere to crust to atmosphere over time
Estimate ~25 million years or more for this to occur on Earth

25. Carbon Dioxide Cycle Step 1: Evaporation/Rain
Liquid water evaporates
Condenses into clouds in lower atmosphere
Rain falls through atmosphere forming Carbonic Acid (H2CO3)
 CO2 gas is absorbed 1

26. Carbon Dioxide Cycle Step 2: Mineral Erosion by Acid Rain
Carbonic Acid (H2CO3) in rivers erodes rocks
Carbonate (CO32-) ion picked up in minerals washed to ocean
Calcium easily absorbed
 CO2 is carried to oceans 2

27. Carbon Dioxide Cycle Step 3: Tying Carbon into Rocks & Life!
Calcium from rocks forms CaCO3 (Calcium Carbonate)
CaCO3 = Limestone
CaCO3 = Coral, Mollusk shells! 3
 CO2 accumulates on seafloor

28. Carbon Dioxide Cycle Step 4: Tectonics & Subduction!
Tectonics gradually pulls seafloor down
CaCO3 broken back into CO2 & other minerals 4
 CO2 now inside crust

29. Carbon Dioxide Cycle Step 5: Volcanic Outgassing!
Eventual Volcanic Activity pushes CO2 back into atmosphere 5
 CO2 now in atmosphere again!

30. Carbon Dioxide Cycle Venus Feedback Loop Failure
Too Hot for clouds to form low enough
But…
Volcanoes don’t stop! 1 5

31. Carbon Dioxide Cycle Venus Feedback Loop Failure
No Rain
NO CO2 gas absorbed
More CO2 added!
Runaway Greenhouse Effect! 1