1. Note that the following lectures include animations and PowerPoint effects such as fly ins and transitions that require you to be in PowerPoint's Slide Show mode (presentation mode).

2. Comparative Planetology of Venus and Mars
Chapter 22
Comparative Planetology of Venus and Mars

3. Guidepost
You have been to the moon and to Mercury, but you are going to find Venus and Mars dramatically different. They have internal heat and atmospheres. The internal heat means they are geologically active, and the atmospheres mean they have weather. As you explore you will discover answers to six essential questions:
Why is the atmosphere of Venus so thick?
What is the hidden surface of Venus really like?
How did Venus form and evolve?
Why is the atmosphere of Mars so thin?
Has Mars ever had water on its surface?
How did Mars form and evolve?

4. Guidepost (continued)
The question always on your mind when you explore other worlds is this: Why is this world so different from Earth? You will see that small initial differences can have big effects.
As you study worlds you cannot visit you will find an answer to an important question about how scientists think:
How can scientists remain honest if they manipulate their data?
You are a planetwalker, and you are becoming an expert on the kind of planets you can imagine walking on. But there are other worlds beyond Mars in our solar system so peculiar they have no surface to walk on, even in your imagination. You will explore them in the next two chapters.

5. Outline I. Venus A. The Rotation of Venus B. The Atmosphere of Venus
I. Venus
A. The Rotation of Venus
B. The Atmosphere of Venus
C. The Venusian Greenhouse
D. The Surface of Venus
E. Volcanism on Venus
F. A History of Venus
II. Mars
A. The Canals of Mars
B. The Atmosphere of Mars
C. The Geology of Mars
D. Finding the Water on Mars
E. A History of Mars
III. The Moons of Mars
A. Origin and Evolution

6. Build a Planet Create your own planet
Create your own planet
Include it’s “vital statistics” (1 page)
Make a picture/diagram of your planet (1 page)
(overall picture of planet and surface feature picture)
4. Your planet will be used in tomorrow’s project
Vital statistics:
Name; origin of the name given; Distance from sun; relative size; # planet from sun; Orbital period, day/night rotation; Tilt/seasons?; core and surface features; name of some prominent features; average day/night temperature; habitable?; Life found?; Gravity; atmosphere; star/galaxy?; water; volcanoes; moons?
Most features, such as size, can be as compared to the Earth

7. Venus and Mars Two most similar planets to Earth:
Two most similar planets to Earth:
Similar in size and mass
Atmosphere
Same part of the solar system
Similar interior structure
Yet, no life possible on either one of them.

8. The Rotation of Venus
Almost all planets rotate counterclockwise, i.e. in the same sense as orbital motion.
Exceptions: Venus, Uranus and Pluto
Venus rotates clockwise, with period slightly longer than orbital period.
Possible reasons:
Off-center collision with massive protoplanet
Tidal forces of the sun on molten core

9. The Atmosphere of Venus
4 thick cloud layers ( surface invisible to us from Earth).
UV image
UV image
Very stable circulation patterns with high-speed winds (up to 240 km/h)
Extremely inhospitable:
96 % carbon dioxide (CO2)
Very efficient “greenhouse”!
3.5 % nitrogen (N2)
Rest: water (H2O), hydrochloric acid (HCl), hydrofluoric acid (HF)
Extremely high surface temperature up to 745 K (880 oF)

10. The Clouds of Venus
Venus is covered with a dense layer of clouds that hides its surface.
Unlike the benign water vapor clouds on Earth, these clouds contain large amounts of sulfur dust and sulfur compounds, giving them a yellow-orange color.
The clouds on Venus are made of concentrated sulfuric acid.

11. We see dramatic increases in both pressure and temperature as we approach the surface of Venus.
At the surface, the temperature is an astounding 860F, even hotter than Mercury.

12. The extreme heating of Venus’ surface is caused by the greenhouse effect
The carbon dioxide in the atmosphere of Venus acts as a “greenhouse,” trapping the heat from the Sun underneath and the temperature rising until finally thermal equilibrium is reached…when the surface is 860F!

13. The Surface of Venus
Early radar images already revealed mountains, plains, craters.
More details from orbiting and landing spacecraft:
Venera 13 photograph of surface of Venus:
Colors modified by clouds in Venus’s atmosphere
After correction for atmospheric color effect:

14. This image of Venus’s surface from the Soviet spacecraft Venera 13 shows rock plates that may be fractured lava.
Unfortunately, this craft was destroyed by the intense pressure and extreme temperatures on the Venusian surface.

15. The Magellan spacecraft, in an orbit around Venus, was able to “see through” the thick clouds using radar, giving us the best view of our sister planet.

16. Radar Map of Venus’s Surface
Surface features shown in artificial colors
Scattered impact craters
Volcanic regions
Smooth lava flows

17. A global view of Venus using radar images from the Magellan spacecraft
The craters found on Venus tend to be in clusters.
This suggests that they were formed from a large single piece of falling debris that was broken up by Venus’s atmosphere.

18. This false color map of Venus, equivalent to a topographical map of Earth, shows the large-scale surface features of the planet.

19. Lava Flows
Young, uneven lava flows (shown: Lava flow near Flagstaff, AZ) show up as bright regions on radar maps.

20. Surface Features on Venus
Maxwell Montes are ~ 50 % higher than Mt. Everest!
Smooth lowlands
Highland regions:

21. Craters on Venus Nearly 1000 impact craters on Venus’s surface:
Nearly 1000 impact craters on Venus’s surface:
 Surface not very old.
No water on the surface; thick, dense atmosphere
 No erosion
 Craters appear sharp and fresh

22. This type of volcanism is not found on Venus or Mars.
Volcanism on Earth
Volcanism on Earth is commonly found along subduction zones (e.g., Rocky Mountains).
This type of volcanism is not found on Venus or Mars.

23. All volcanoes on Venus and Mars are shield volcanoes
Found above hot spots:
Fluid magma chamber, from which lava erupts repeatedly through surface layers above.
All volcanoes on Venus and Mars are shield volcanoes

24. Example: The Hawaiian Islands
Shield Volcanoes (2)
Tectonic plates moving over hot spots producing shield volcanoes  Chains of volcanoes
Example: The Hawaiian Islands

25. Volcanism on Venus Sapas Mons (radar image) ~ 400 km (250 miles)
Sapas Mons (radar image)
~ 400 km (250 miles)
2 lava-filled calderas
Lava flows

26. Volcanic Features on Venus
Aine Corona
Baltis Vallis: 6800 km long lava flow channel (longest in the solar system!)
Coronae: Circular bulges formed by volcanic activity
Some lava flows collapsed after molten lava drained away
Pancake Domes:
Associated with volcanic activity forming coronae

27. Lakshmi Planum and Maxwell Mountains
Radar image
Wrinkled mountain formations indicate compression and wrinkling, though there is no evidence of plate tectonics on Venus.

28. A History of Venus Complicated history; still poorly understood.
Complicated history; still poorly understood.
Very similar to Earth in mass, size, composition, density,
but no magnetic field  Core solid?
 Solar wind interacts directly with the atmosphere, forming a bow shock and a long ion tail.
CO2 produced during outgassing remained in atmosphere (on Earth: dissolved in water).
Any water present on the surface rapidly evaporated → feedback through enhancement of greenhouse effect
Heat transport from core mainly through magma flows close to the surface ( coronae, pancake domes, etc.)

29. Build a Solar System Create your own planet (yesterday)
Create your own planet (yesterday)
Which Galaxy does it belong and which star does it orbit in that Galaxy?
Create 10 more objects in that solar system.
Give a detailed description on paper of each of the 10 objects, they could be planets, moons, asteroids, etc…(location/ planet type/orbital and rotational period/life?/ name/relative size(compared to your original planet))
Create a diagram of your solar system, must be in color
Label each part in the diagram

31. Mars has been the Center of Speculation about Extraterrestrial Life
People feared an attack from Mars, like this one portrayed in “The War of the Worlds.”
Early telescope images showed features which were perceived as irrigation canals.

32. Mars Diameter ≈ 1/2 Earth’s diameter Very thin atmosphere, mostly CO2
Diameter ≈ 1/2 Earth’s diameter
Very thin atmosphere, mostly CO2
Rotation period = 24 h, 40 min.
Axis tilted against orbital plane by 25o, similar to Earth’s inclination (23.5o)
Seasons similar to Earth  Growth and shrinking of polar ice cap
Crust not broken into tectonic plates
Volcanic activity (including highest volcano in the solar system)

33. Tales of Canals and Life on Mars
Early observers (Schiaparelli, Lowell) believed to see canals on Mars
This, together with growth/shrinking of polar cap, sparked imagination and sci-fi tales of life on Mars.
We know today: “canals” were optical illusion; do not exist!
No evidence of life on Mars.

34. Topographical Map of Mars

35. The Martian surface includes broad towering volcanoes, vast windswept plains, and enormous canyons.
Valles Marineris is a vast canyon stretchimg over about one-fifth the circumference of Mars (as wide as the United States).

36. Very thin: Only 1% of pressure on Earth’s surface
The Atmosphere of Mars
Very thin: Only 1% of pressure on Earth’s surface
95 % CO2
Even thin Martian atmosphere evident through haze and clouds covering the planet
Occasionally: Strong dust storms that can enshroud the entire planet.

37. The Atmosphere of Mars (2)
Most of the Oxygen bound in oxides in rocks
 Reddish color of the surface

38. History of Mars’s Atmosphere
Atmosphere probably initially produced through outgassing.
Loss of gasses from a planet’s atmosphere:
Compare typical velocity of gas molecules to escape velocity
Gas molecule velocity greater than escape velocity  gasses escape into space.
Mars has lost all lighter gasses; retained only heavier gasses (CO2).

39. History of Mars’s Atmosphere
Gases bound in the polar cap are returned to the atmosphere each spring in spots and fans

40. Reddish deserts of broken rock, probably smashed by meteorite impacts.
The Geology of Mars
Giant volcanoes
Valleys
Impact craters
Reddish deserts of broken rock, probably smashed by meteorite impacts.
Vallis Marineris

41. Impact Craters on Mars
Most of these craters are found in the Southern Hemisphere, suggesting that the Northern Hemisphere has been resurfaced.

42. The Martian surface also has some unusual features
22 years later, with improved technology, the feature looks more natural.
Apparent “face” on the Martian surface.

43. The Geology of Mars (2)
The surface features on Mars have most recently been explored close-up by the Mars rovers Spirit and Opportunity.

44. The Geology of Mars (2) Possibly once filled with water.
Possibly once filled with water.
Northern Lowlands: Free of craters; probably re-surfaced a few billion years ago.
Southern Highlands: Heavily cratered; probably 2 – 3 billion years old.

45. Volcanism on Mars Olympus Mons:
Volcanoes on Mars are shield volcanoes.
Olympus Mons:
Highest and largest volcano in the solar system.

46. Volcanism on Mars (2) Tharsis rise (volcanic bulge):
Tharsis rise (volcanic bulge):
Nearly as large as the U.S.
Rises ~ 10 km above mean radius of Mars.
Rising magma has repeatedly broken through crust to form volcanoes.

47. Mars also has volcanoes. The largest of these is Olympus Mons
Mars also has volcanoes. The largest of these is Olympus Mons. It covers an area the size of Missouri and rises three times higher than Mount Everest.

48. Martian Seasons
Mars is tilted on its axis by 25.19 (nearly the same as Earth) and the hemispheres experience seasons that can be observed by examining the polar caps.
Large ice cap made mostly of frozen carbon dioxide (dry ice)
The dry ice sublimates, leaving a much smaller polar cap

49. Although it is sometimes blue, the Martian sky generally takes on a rust color because of dust particles blown into the atmosphere by strong winds.

50. High winds create dust devils on the Martian surface.
DARK STREAKS SHOW THE PATH OF DUST DEVILS
A DUST DEVIL FROM ABOVE

51. Hidden Water on Mars No liquid water on the surface:
No liquid water on the surface:
Would evaporate due to low pressure.
But evidence for liquid water in the past:
Outflow channels from sudden, massive floods
Collapsed structures after withdrawal of sub-surface water
Valleys resembling meandering river beds
Gullies, possibly from debris flows
Central channel in a valley suggests long-term flowing water

52. Sedimentary rock layers, formed by rapidly flowing water.
Hidden Water on Mars (2)
Hematite concretions in Martian Rocks, photographed by the Mars Rover Opportunity
Sedimentary rock layers, formed by rapidly flowing water.

53. Evidence for Water on Mars
Galle,
the “happy face crater”
Meteorite ALH84001:
Identified as ancient rock from Mars.
Some minerals in this meteorite were deposited in water  Martian crust must have been richer in water than it is today.
Large impacts may have ejected rocks into space.

54. The winding canyons found on the Martian surface are similar to those found in river beds on Earth, suggesting that liquid water once flowed on Mars.
The Yangtze River in China has similar features
Martian winding canyon, photographed by the Viking orbiter

55. Surface features believed to be ancient waterways
A dried riverbed
An ancient lake
Sedimentation

56. Layers of rock laid down by water
Hematite black rocks, usually formed in water
Gullies in crater walls

57. Did Mars once support life? Is there life there now?
Viking’s mechanical arms collect samples of the Martian soil to analyze its chemical makeup and to search for possible signs of microscopic life.

58. SNC meteorites are believed to have come from Mars, because their chemistry is consistent with that of the Martian climate. These would have been ejected from Mars during a major impact.
These rocks show possible fossils of microbial life. However, they also have possible non-biological explanations.

59. The History of Mars Differentiated when it formed a hot, molten core
Differentiated when it formed a hot, molten core
Cooled off rapidly
→ Mostly solid core can not produce an overall magnetic field.
Three main periods:
Noachian Period
4.3 – 3.7 bil. years ago
Heavy meteorite bombardment;
Flooding of plains by great lava flows;
Liquid surface water could have been present.
Hesperian period
3.7 – 3 bil. years ago
Part of surface covered by lava flows;
Outflow channels may have formed;
Formation of the Tharsis rise might have decreased the orbital tilt of the rotation axis from ~ 45o to the present 25o
Amazonian Period
3 bil. yrs. ago – today
Mostly uneventful;
Thick crust prevents geological activity.

60. The Moons of Mars Probably captured from outer asteroid belt.
Two small moons: Phobos and Deimos.
Too small to pull themselves into spherical shape.
Typical of small, rocky bodies: Dark grey, low density.
Phobos
Very close to Mars; orbits around Mars faster than Mars’ rotation.
Probably captured from outer asteroid belt.
Deimos

61. The two moons of Mars, Deimos and Phobos, are small and non-spherical in shape. These are planetesimals captured by Mars.

64. WHAT DID YOU THINK?
Which of the two planets, Mercury (the closest planet to the Sun) or Earth, has the coolest temperature?
The daytime temperature of Mercury is much higher than on Earth, but the nighttime temperature of Mercury is much lower than on Earth.
Which planet is most similar to Earth?
Venus is most similar in size, chemistry, and distance from the Sun. Mars is most similar in its length of day, seasons, erosion, and in having water ice.
What is the composition of the clouds surrounding Venus?
The clouds are made primarily of sulfuric acid.

65. WHAT DID YOU THINK? Does Mars have liquid water on its surface today?
No, but there are strong indications that it had liquid water in the past.
Is life known to exist on Mars today?
No current life has yet been discovered on Mars.