1. Chapter 6 The Terrestrial Planets

2. Chapter 6 The Terrestrial Planets

3. Units of Chapter 6 Orbital and Physical Properties Rotation Rates
Atmospheres
The Surface of Mercury
The Surface of Venus
The Surface of Mars
Internal Structure and Geological History
Atmospheric Evolution on Earth, Venus, and Mars

4. Sputnik 1

5. Question 1
Which of the following inner solar system bodies has the largest volcanoes?
a) Mercury
b) Venus
c) Earth
d) Mars
e) Moon
Answer: d

6. Question 1
Which of the following inner solar system bodies has the largest volcanoes?
a) Mercury
b) Venus
c) Earth
d) Mars
e) Moon
Mars’ largest volcano, Olympus Mons, rises more than 25 km (75,000 ft) above the surrounding plains.

7. Orbital and Physical Properties
The orbits of Venus and Mercury show that these planets never appear far from the Sun.

8. Orbital and Physical Properties
The terrestrial planets have similar densities and roughly similar sizes, but their rotation periods, surface temperatures, and atmospheric pressures vary widely.

9. Rotation Rates
Mercury can be difficult to image from Earth; rotation rates can be measured by radar.

10. Rotation Rates
Mercury was long thought to be tidally locked to the Sun; measurements in 1965 showed this to be false.
Rather, Mercury’s day and year are in a 3:2 resonance; Mercury rotates three times while going around the Sun twice.

11. Rotation Rates
Venus
Mars
-243 days
1.03 days

12. Rotation Rates
All the planets rotate in a prograde direction, except Venus, which is retrograde.

13. Question 2
a) Mercury
b) Venus
c) Earth
d) Moon
e) Mars
Which of the following inner solar system bodies has the densest atmosphere?
Answer: b

14. Question 2
a) Mercury
b) Venus
c) Earth
d) Moon
e) Mars
Which of the following inner solar system bodies has the densest atmosphere?
Venus’ atmosphere has a pressure about 90 times larger than Earth’s.
Many of its surface features are affected by this immense pressure.

15. Atmospheres
Mercury has no detectable atmosphere; it is too hot, too small, and too close to the Sun.
Venus has an extremely dense atmosphere. The outer clouds are similar in temperature to Earth, and it was once thought that Venus was a “jungle” planet We now know that its surface is hotter than Mercury’s, hot enough to melt lead.
The atmosphere of Mars is similar to Earth in composition, but very thin.

16. Question 3
a) nitrogen
b) hydrogen
c) carbon dioxide
d) oxygen
e) sulfuric acid
The greenhouse effect on Venus is due to ______ in its atmosphere.
Answer: c

17. Question 3
a) nitrogen
b) hydrogen
c) carbon dioxide
d) oxygen
e) sulfuric acid
The greenhouse effect on Venus is due to ______ in its atmosphere.
Venus’ atmosphere is over 96% CO2, resulting in a surface temperature exceeding 900 °F.

18. Question 4 Mercury’s surface most resembles which of these?
a) the Moon’s far side
b) Venus’ polar regions
c) Earth’s deserts
d) the Moon’s near side
e) Mars’ deserts
Mercury’s surface most resembles which of these?
Answer: a

19. Both Mercury and the Moon’s far side are heavily cratered.
Question 4
a) the Moon’s far side
b) Venus’ polar regions
c) Earth’s deserts
d) the Moon’s near side
e) Mars’ deserts
Mercury’s surface most resembles which of these?
Both Mercury and the Moon’s far side are heavily cratered.

20. The Surface of Mercury
Mercury cannot be imaged well from Earth; best pictures are from Messenger.
Cratering on Mercury is similar to that on the Moon.

21. Messenger Selected 1999 Launched 2004 Orbit insertion 2011
$446 Billion
5 Billion miles

23. Question 5 Mercury is very hard to observe from Earth because
a) it always appears only half lit.
b) it is never more than 28° from the Sun.
c) its elliptical orbit causes it to change speed unpredictably.
d) its surface reflects too little sunlight.
e) its surface does not allow radar to bounce back to Earth.
Mercury is very hard to observe from Earth because
Answer: b

24. Question 5 Mercury is very hard to observe from Earth because
a) it always appears only half lit.
b) it is never more than 28° from the Sun.
c) its elliptical orbit causes it to change speed unpredictably.
d) its surface reflects too little sunlight.
e) its surface does not allow radar to bounce back to Earth.
Mercury is very hard to observe from Earth because
Mercury’s inner orbit keeps it close to the Sun, visible only for an hour or two before sunrise or after sunset.

25. The Surface of Mercury
Some distinctive features: Scarp (cliff), several hundred km long and up to 3 km high, thought to be formed as the planet cooled and shrank.

26. The Surface of Mercury
Caloris Basin, very large impact feature; ringed by concentric mountain ranges

27. Question 6
a) it is so close to the Sun.
b) its surface rocks don’t retain heat.
c) it spins too fast to cool down.
d) Mercury’s axis has no tilt; its equator receives direct sunlight.
e) it has no atmosphere to moderate temperatures over the globe.
Mercury has extreme high and low temperatures between night and day because
Answer: e

28. Question 6
a) it is so close to the Sun.
b) its surface rocks don’t retain heat.
c) it spins too fast to cool down.
d) Mercury’s axis has no tilt; its equator receives direct sunlight.
e) it has no atmosphere to moderate temperatures over the globe.
Mercury has extreme high and low temperatures between night and day because
Mercury’s very high sunlit surface temperature of 700 K, and low mass, explain why it has no atmosphere.

29. The Surface of Venus
This map of the surface features of Venus is on the same scale as the Earth map below it.

30. The Surface of Venus
Venus as a globe, imaged by Magellan launched from STS-30 in 1989.
730 k = HOT!
855 F
90 atm
Sulfuric acid rain

31. Question 7 Venus’ surface shows all of the following EXCEPT
a) many impact craters of all sizes.
b) shield volcanoes.
c) a continent-sized plateau.
d) huge circular volcanic coronae.
e) lava domes.
Venus’ surface shows all of the following EXCEPT
Answer: a

32. Question 7 Venus’ surface shows all of the following EXCEPT
a) many impact craters of all sizes.
b) shield volcanoes.
c) a continent-sized plateau.
d) huge circular volcanic coronae.
e) lava domes.
Venus’ surface shows all of the following EXCEPT
Venus’ thick atmosphere shields the planet from smaller meteor impacts.

33. The Surface of Venus
Top: Lava domes on Venus (L), and a computer reconstruction (R)
Bottom: the volcano Gula Mons

34. The Surface of Venus
Venus corona, with lava domes
Fly by

35. The Surface of Venus
A photograph of the surface, from the Venera lander. Russia sent more than 16 probes.

36. Photography on Venus

37. Venera - USSR

38. The Surface of Venus
Impact craters. Left: multiple-impact crater Above: Mead, Venus’s largest impact crater

39. Mars

40. The Surface of Mars
Major feature: Tharsis bulge, size of North America and 10 km above surroundings
Minimal cratering; youngest surface on Mars

41. Viking I & II 1976

42. Viking 1976

43. The Surface of Mars
Northern hemisphere (left) is rolling volcanic terrain.
Southern hemisphere (right) is heavily cratered highlands; average altitude 5 km above northern.
Assumption is that northern surface is younger than southern.
Means that northern hemisphere must have been lowered in elevation and then flooded with lava.
Fly by

44. The Surface of Mars
This map shows the main surface features of Mars. There is no evidence for plate tectonics.

45. The Surface of Mars
Mars has largest volcano in Solar System; Olympus Mons:
700 km diameter at base
25 km high
Caldera 80 km in diameter
Three other Martian volcanoes are only slightly smaller.

46. The Surface of Mars Was there running water on Mars?
Runoff channels resemble those on Earth.
Left: Mars
Right: Earth

47. The Surface of Mars
No evidence of connected river system; features probably due to flash floods

48. The Surface of Mars
This feature may be an ancient river delta. Or it may be something entirely different.
Okavango

49. 6.6 The Surface of Mars
Much of northern hemisphere may have been ocean.

50. The Surface of Mars
Impact craters less than 5 km across have mostly been eroded away.
Analysis of craters allows estimation of age of surface.
Crater on right was made when surface was liquid.

51. Question 8
a) rainfall
b) catastrophic but rare flooding
c) annual melting of the seasonal ice caps
d) large comets that struck Mars
e) a collision with one of Jupiter’s frozen moons
What was the most likely source of the water that formed the huge outflow channels of Mars?
Answer: b

52. Flooding on Mars appears to have occurred about 3 billion years ago.
Question 8
a) rainfall
b) catastrophic but rare flooding
c) annual melting of the seasonal ice caps
d) large comets that struck Mars
e) a collision with one of Jupiter’s frozen moons
What was the most likely source of the water that formed the huge outflow channels of Mars?
Flooding on Mars appears to have occurred about 3 billion years ago.

53. The Surface of Mars
Recently, gullies have been seen that seem to indicate the presence of liquid water; interpretation is still in doubt.

54. The Surface of Mars Left: Viking photo
Right: Mars rover Sojourner, approaching “Yogi”

55. The Surface of Mars
Landscape and close-up by Opportunity rover

56. Opportunity Rover $ 1 Billion
Manned mission estimate of more than $10 Billion

57. RAT & Möessbauer

58. Internal Structure and Geological History
Internal structure of Mercury, Mars, and the Moon, compared to Earth

59. Atmospheric Evolution on Earth, Venus, and Mars
At formation, planets had primary atmosphere – hydrogen, helium, methane, ammonia, water vapor – which was quickly lost.
Secondary atmosphere – water vapor, carbon dioxide, sulfur dioxide, nitrogen – comes from volcanic activity.
Earth now has a tertiary atmosphere, 20 percent oxygen, due to the presence of life.

60. Atmospheric Evolution on Earth, Venus, and Mars
Earth has a small greenhouse effect; it is in equilibrium with a comfortable (for us) surface temperature.

61. Atmospheric Evolution on Earth, Venus, and Mars
Venus’s atmosphere is much denser and thicker; a runaway greenhouse effect has resulted in its present surface temperature of 730 K.

63. Summary of Chapter 6
Mercury is tidally locked in a 3:2 ratio with the Sun.
Mercury has no atmosphere; Venus has a very dense atmosphere, whereas the atmosphere of Mars is similar to Earth in composition but very thin.
Mercury has no maria, but does have extensive intercrater plains and scarps.

64. Summary of Chapter 6, cont.
Venus is never too far from the Sun, and is the brightest object in the sky (after the Sun and Moon).
It has many lava domes and shield volcanoes.
Venus is comparable to Earth in mass and radius.
Large amount of carbon dioxide in atmosphere, and closeness to the Sun, led to runaway greenhouse effect and very hot surface.

65. Summary of Chapter 6, cont.
Northern and southern hemispheres of Mars are very different.
South is higher and heavily cratered.
North is lower and relatively flat.
Major features: Tharsis bulge, Olympus Mons, Valles Marineris
Strong evidence for water on Mars in the past

66. Summary of Chapter 6, cont.
Mercury has very weak, remnant magnetic field.
Venus has none, probably because of very slow rotation.
Neither Venus nor Mars show signs of substantial tectonic activity.