1. Chapter 7 Earth and the Terrestrial Worlds

2. Why is Venus so hot?

3. 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.

4. 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)

5. 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)

6. 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)

7. 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)

8. 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)

9. 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)

10. 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)

11. 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])

12. Does Venus have plate tectonics?
Earth’s major geological features can be attributed to plate tectonics, which gradually remakes our surface.
Venus does not appear to have plate tectonics, but its entire surface seems to have been “repaved” 750 million years ago.

13. Why is Venus so hot?

14. 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)

15. Atmosphere of Venus
Venus has a very thick carbon dioxide atmosphere with a surface pressure 90 times that of Earth.

16. Atmosphere of Venus
Reflective clouds contain droplets of sulfuric acid.
The upper atmosphere has fast winds that remain unexplained.

17. Venus’ Atmosphere
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])

18. 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.

19. Venus’ Atmosphere 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

20. Greenhouse Effect on Venus
Thick carbon dioxide atmosphere produces an extremely strong greenhouse effect.
Earth escapes this fate because most of its carbon and water are in rocks and oceans.

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

22. Explaining Venus’ Atmosphere
Lots of Volcanoes
CO2, H2S04 are outgassed
CO2 traps infrared heat from Sun
Atmosphere heats up
Water can’t condense => No Rain!
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)

23. 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.

24. 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.

25. 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.

26. 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

27. Carbon Dioxide Cycle
How do atmospheres of Venus & Mars differ in their ability to cycle CO2 from atmosphere to crust and back??

28. Carbon Dioxide Cycle
Assume all 3 planets had similar compositions and conditions “early” in the solar system’s history…
Assume all 3 had liquid water, active volcanoes, and CO2 in atmosphere

29. 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

30. 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

31. 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

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

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

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

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

36. Carbon Dioxide Cycle Mars Feedback Loop Failure
Evaporation
Rain
CO2 gas flushed out
But…
Interior cools off
Volcanoes Stop! 1 5

37. Carbon Dioxide Cycle Mars Feedback Loop Failure
Atmosphere CO2 decreases
Planet freezes 1 5

38. Mars FIGURE 7-18 Mars This photograph, taken
from space, shows the Arabia Terra (in light
orange) and carbon dioxide snow at the planet’s
poles. (NASA, The Hubble Heritage Team)

39. Schiaparelli’s “Canals”
FIGURE 7-19 The Illusion of Martian Canals
Giovanni Schiaparelli examined Mars through a 20-cm (8-in.) diameter
telescope, the same size used by many amateur
astronomers today. His drawings of the red planet showed
features perceived by Percival Lowell and others as irrigation
canals. Higher resolution images from Earth and spacecraft
visiting Mars failed to show the same features. (Michael
Hoskin, ed., The Cambridge Illustrated History of Astronomy,
Cambridge University Press, 1997, p Illustration by G. V.
Schiaparelli. Courtesy of Institute of Astronomy, University of
Cambridge, UK)

40. FIGURE 7-24 In the Eye of the Beholder
These two images of the same site on Mars, taken 22
years apart, show how the apparent face in (a)
changed to a more “natural-looking” feature in (b) This transformation
was due to weathering of the site, improved camera
technology, and the change in angle at which the photograph
was taken.

41. FIGURE 7-24 In the Eye of the Beholder
These two images of the same site on Mars, taken 22
years apart, show how the apparent face in (a)
changed to a more “natural-looking” feature in (b) This transformation
was due to weathering of the site, improved camera
technology, and the change in angle at which the photograph
was taken.

42. Pyramids Happy Faces! More illusions:
FIGURE 7-24 In the Eye of the Beholder
(c) In the same region of Mars, other erosion
features also appear to be pyramids and skulls. (d) The
Galle crater and its interior features combine to give the
impression of a “happy face.” (a and b: NSSDC/NASA;
NASA/JPL/Malin Space Science Systems; c and d:
©ESA/DLR/FU Berlin [G. Neu Kum])

43. A Martian Sunset… FIGURE 7-26 The Atmosphere of Mars
(a) When Mars’s sky is relatively free of dust, it appears similar in color to our sky,
as shown in this sunset photo taken by the rover Opportunity.
The darker, brown color in which the Sun is immersed is due
to lingering dust in the sky. When less dust is present, the Sun
looks almost white during Martian sunsets. Most of the images
we have of Mars’s sky show colors like that seen in (b).

44. Mars vs. Earth 50% Earth’s radius, 10% Earth’s mass
1.5 AU from the Sun
Axis tilt about the same as Earth
Similar rotation period (25 hours/”day”)
Thin CO2 atmosphere: little greenhouse effect
=>Main difference: Mars is SMALLER

45. Seasons on Mars
Seasons on Mars are more extreme in the southern hemisphere because of its elliptical orbit.

47. Storms on Mars
Seasonal winds on Mars can drive huge dust storms.

48. What geological features tell us water once flowed on Mars?

49. The surface of Mars appears to have ancient riverbeds.

50. Eroded crater
The condition of craters indicates surface history.

51. Close-up of eroded crater

52. The Martian Surface Map
FIGURE 7-20 The Topography of Mars
The color coding on this map of Mars shows elevations
above (positive numbers) or below (negative numbers)
the planet’s average radius. To produce this map, an
instrument on board Mars Global Surveyor fired pulses of laser
light at the planet’s surface, then measured how long it took
each reflected pulse to return to the spacecraft. The Viking 1
Lander (VL1), Viking 2 Lander (VL2), Mars Pathfinder (MP),
Opportunity, and Spirit landing sites are each marked with an
X. (MOLA Science Team, NASA/GSFC)

53. Need Figure 7.20.

54. Volcanoes…as recent as 180 million years ago…
Meteoritic evidence, radiometric dating
Volcanoes…as recent as 180 million years ago…

55. Past tectonic activity…

56. A *really* GRAND canyon…
FIGURE 7-21 Martian Terrain
This high-altitude photograph
shows a variety of the features on Mars, including broad, towering
volcanoes (left) on the highland, called Tharsis Bulge;
impact craters (upper right); and vast, windswept plains. The
enormous Valles Marineris canyon system crosses horizontally
just below the center of the image. Inset: Details of the Valles
Marineris, which is about 100 km (60 mi) wide. The canyon
floor has two major levels. The northern (upper) canyon floor
is 8 km (5 mi) beneath the surrounding plateau, whereas the
southern canyon floor is only 5 km (3 mi) below the plateau.
(USGS/NASA; inset: NASA/GSFP/LTP)

57. A *even bigger* volcano
FIGURE 7-23 The Olympus Caldera
(a) This view of the summit of Olympus Mons is based on
a mosaic of six pictures taken by one of the
Viking orbiters. The caldera consists of overlapping, volcanic
craters and measures about 70 km across. The volcano is
wreathed in mid-morning clouds brought upslope by cool air
currents. The cloud tops are about 8 km below the volcano’s
peak.

58. FIGURE 7-23 The Olympus Caldera
(b) These cones on Mars may have been created when
lava from Olympus Mons heated underground ice, causing
the resulting water and vapor to expand, raise the planet’s surface,
and burst out. (Peter Lanagan [LPL, U. Arizona] et al., MOC.
MGS. NASA)

59. Differences in Hemispheres
FIGURE 7-22 Craters on Mars
This image was made during
the opposition of Arabia Terra looks like the
Arabian peninsula on Earth. It is an old, highly eroded region
dotted with numerous flat-bottom craters. Lava-covered Syrtis
Major was first identified by Christiaan Huygens in A
single impact carved out Hellas Planitia, which is five times
the size of Texas. Inset: This mosaic of images from the Viking
1 and 2 orbiter spacecraft shows an extensively cratered
region located south of the Martian equator. Note how worn
down these craters are compared to those on Mercury and
our Moon. (NASA; J. Bell, Cornell University; and M. Wolff, SSI;
inset: USGS)

60. Low-lying regions may once have had oceans.

61. Low-lying regions may once have had oceans.

62. Opportunity
Spirit
Inset shows hypothetical ancient ‘water line’ for Gusev Crater where Spirit landed
NASA’s SPIRIT & OPPORTUNITY Rovers…still sending data!

63. 2004 Opportunity Rover provided strong evidence for abundant liquid water on Mars in the distant past.
How could Mars have been warmer and wetter in the past?

64. Today, most water lies frozen underground (blue regions)
Some scientists believe accumulated snowpack melts carve gullies even today.

65. Why did Mars change?

66. Climate Change on Mars
No widespread surface water for 3 billion years.
Greenhouse effect probably kept surface warmer before.
Somehow Mars lost most of its atmosphere.

67. Climate Change on Mars
Magnetic field may have preserved early Martian atmosphere.
Solar wind may have stripped atmosphere after field decreased because of interior cooling.

68. Polar Climate Change FIGURE 7-25 Changing Seasons on Mars
During the Martian winter, the temperature
decreases so much that carbon
dioxide freezes out of the
Martian atmosphere. A thin coating
of carbon dioxide frost covers
a broad region around Mars’s
north pole. During the summer in
the northern hemisphere, the
range of this north polar carbon
dioxide cap decreases dramatically.
During the summer, a ring
of dark sand dunes is exposed
around Mars’s north pole. (S.
Lee/J. Bell/M. Wolff/Space Science
Institute/NASA)

69. Exploring Mars FIGURE 7-26 The Atmosphere of Mars
(b) Taken by the Mars Pathfinder, this photograph shows the
Sojourner rover snuggled against a rock named Moe on the
Ares Vallis to run tests on the rock. At the top of the image, the
pink color of the Martian sky is evident. (NASA/Lunar and
Planetary Institute)

70. Winds on Mars FIGURE 7-27 Martian Dust Devil
(a) This Spirit image is one
in a movie sequence of a dust devil moving left to right across
the surface of Mars. The rovers have filmed several such
events.

71. Wind trails from “dust devils”
FIGURE 7-27 Martian Dust Devil
(b) These dark streaks are the paths of dust devils on
the Argyre Planitia of Mars. The tracks cross hills, sand dunes,
and boulder fields, among other features on the planet’s surface.
(a: NASA/JPL; b: NASA/JPL/Malin Space Science Systems)

72. Rivers on Mars … & Earth! FIGURE 7-29 Rivers on Mars and Earth
(a) Winding canyons on Mars, such as the one in this Viking 1 orbiter
image, appear to be due to sustained water flow. This belief
is supported by the terraces seen on the canyon walls in
high-resolution Mars Orbiter images. Long periods of water
flow require that the planet’s atmosphere was once thicker
and its climate more Earthlike. (b) Yangtze River near
Chongqing, China. Typical of rivers on Earth, it shows the
same snakelike curve as the river channels on Mars.
(a: NASA; b: TMSC/NASA)
… & Earth!

73. FIGURE 7-31 Ancient Oceans and Lakes on Mars
(a) This Mars Global Surveyor image of a portion of
Valles Marineris reveals terrain with “stair-step layers.”
Such terrain is likely to have been created by sedimentation
at the bottom of an ancient body of water (a: Malin Space Science
Systems/JPL/NASA; b: [NASA/JPL/Cornell])

74. FIGURE 7-31 Ancient Oceans and Lakes on Mars
(b) This image of
Burns Cliff, photographed by rover Opportunity, shows a closeup
of layers of rock laid down on a body of water on Mars that
went through wet and dry periods. (a: Malin Space Science
Systems/JPL/NASA; b: [NASA/JPL/Cornell])

75. FIGURE 7-32 Layers of Rock Laid Down by Water
(a) This close-up image taken by the rover
Opportunity shows a small section of rock layers in
a location, called The Dells. The angled and curved layering
seen here is created only on Earth by water flow, strongly suggesting
that this sediment was also deposited by water. The
nearly spherical rocks, called “blueberries,” because they are
dark, have been chemically identified as hematite, an iron-rich
mineral that is usually formed in water. The rovers have found
blueberries strewn in a wide variety of locations. (a: NASA/JPL/USGS;
b: NASA/JPL/Cornell)

76. FIGURE 7-32 Layers of Rock Laid Down by Water
(b) This iron meteorite, dubbed the “Heat Shield Rock” because it was
discovered behind the Mars rover Sojourner’s heat shield, is
surrounded by hematite blueberries. (a: NASA/JPL/USGS;
b: NASA/JPL/Cornell)

77. FIGURE 7-33 Martian Gullies (a, b) Two images of the
same southern hemisphere crater on Mars taken six years
apart. Although not incontrovertible, they provide strong evidence
for recent water flow from inside the red planet. The
reason it occurred now is still under investigation.
(NASA/JPL/Malin Space Science Systems)

78. … More evidence of water
FIGURE 7-33 Martian Gullies
(c) Polygonal cracks are visible in this Opportunity image
of Escher Rock. They were believed to have formed when
this area was flooded. Water seeped into the rock, which
cracked as the water froze and expanded, then evaporated
away. (NASA/JPL/Cornell)

79. FIGURE 7-34 A Piece of Mars on Earth
Mars’s thin atmosphere does little to protect it from impacts. Some of the debris
ejected from impact craters there apparently traveled to Earth.
(a) SNC meteorite recovered in Antarctica. It shows strong evidence
of having been exposed to liquid water on Mars, perhaps
for hundreds of years. (a: NASA; b: NASA/JPL)

80. FIGURE 7-34 A Piece of Mars on Earth
Mars’s thin atmosphere does little to protect it from impacts. Some of the debris
ejected from impact craters there apparently traveled to Earth.
(b) Possible fossil remains of primitive
bacterial life on Mars, although theories of nonbiological
origins have also been presented. (a: NASA; b: NASA/JPL)