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2. Chapter 6 The Terrestrial Planets
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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
Summary of Chapter 6
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4. 6.1 Orbital and Physical Properties
The orbits of Venus and Mercury show that these planets never appear far from the Sun.
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5. 6.1 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.
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6. 6.2 Rotation Rates
Mercury can be difficult to image from Earth, rotation rates can be measured by radar.
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7. 6.2 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.
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8. 6.2 Rotation Rates
Venus
Mars
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9. 6.2 Rotation Rates
All the planets rotate in a prograde direction, except Venus, which is retrograde.
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10. 6.3 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.
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11. 6.4 The Surface of Mercury
Mercury cannot be imaged well from Earth. The best pictures are from Messenger.
Cratering on Mercury is similar to that on the Moon.
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12. 6.4 The Surface of Mercury
A distinctive feature is the scarps (cliffs), several hundred kilometers long and up to 3 km high, is thought to be formed as the planet cooled and shrank.
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13. 6.4 The Surface of Mercury
Caloris Basin, a very large impact feature, ringed by concentric mountain ranges
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14. 6.5 The Surface of Venus
This map of the surface features of Venus is on the same scale as the Earth map below it.
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15. 6.5 The Surface of Venus Venus as a globe, imaged by Magellan
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16. 6.5 The Surface of Venus
Top: Lava domes on Venus (L), and a computer reconstruction (R)
Bottom: The volcano Gula Mons
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17. 6.5 The Surface of Venus Venus corona, with lava domes
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18. 6.5 The Surface of Venus
A photograph of the surface of Venus from the Venera lander
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19. 6.5 The Surface of Venus
Impact craters. Left: multiple-impact crater Above: Mead, Venus’s largest impact crater
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20. 6.6 The Surface of Mars
Major feature: The Tharsis bulge is the size of North America and rises 10 km above its surroundings.
With minimal cratering, it is the youngest surface on Mars.
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21. 6.6 The Surface of Mars
Northern hemisphere (top) is rolling volcanic terrain.
Southern hemisphere (bottom) is heavily cratered highlands; average altitude is 5 km above the northern.
Assumption is that the northern surface is younger than the southern.
This means that the northern hemisphere must have been lowered in elevation and then flooded with lava.
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22. 6.6 The Surface of Mars
This map shows the main surface features of Mars. There is no evidence of plate tectonics.
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23. 6.6 The Surface of Mars
Mars has the largest volcano in the solar system, Olympus Mons:
700 km diameter at base
25 km high
Caldera 80 km in diameter
Four other Martian volcanoes are only slightly smaller.
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24. 6.6 The Surface of Mars Was there running water on Mars?
Runoff channels resemble those on Earth.
Left: Mars
Right: Earth
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25. 6.6 The Surface of Mars
There is no evidence of a connected river system. The features are probably due to flash floods.
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26. 6.6 The Surface of Mars
This feature may be an ancient river delta. Or, it may be something entirely different.
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27. 6.6 The Surface of Mars
Much of the northern hemisphere may have been ocean.
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28. 6.6 The Surface of Mars
Impact craters less than 5 km across have mostly been eroded away.
Analysis of craters allows estimation of the age of the surface.
Crater on right shows ejecta that may have been liquified by the impact that created the crater.
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29. 6.6 The Surface of Mars
Recently, gullies have been seen that probably indicate the occasional presence of liquid water.
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30. Mars rover Curiosity near Mt. Sharp in Gale Crater
6.6 The Surface of Mars
Viking photo
Mars rover Curiosity near Mt. Sharp in Gale Crater
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31. 6.6 The Surface of Mars
Landscape near the north polar cap by the Phoenix lander
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32. 6.7 Internal Structure and Geological History
Internal structure of Mercury, Mars, and the Moon, compared to Earth
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33. 6.8 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.
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34. 6.8 Atmospheric Evolution on Earth, Venus, and Mars
Earth has a small greenhouse effect; it is in equilibrium with a comfortable (for us) surface temperature.
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35. 6.8 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.
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36. 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, and 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.
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37. 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 amounts of carbon dioxide in its atmosphere and closeness to the Sun led to a runaway greenhouse effect and very hot surface.
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38. 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 include the Tharsis bulge, Olympus Mons, Valles Marineris.
There is strong evidence for water on Mars in the past.
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39. 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.
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