Download Chapter10

Chapter 10 - Mercury and Venus
CHAPTER 10
MERCURY AND VENUS
CHAPTER OUTLINE AND LECTURE NOTES
1. Mercury
The way that Mercury’s sidereal rotation period and orbital period combine to yield a solar
day two years long (Figure 10.3) may be hard for some students to grasp unless they are led
through the sequence of orbital and rotational positions shown in the figure. It may be
much easier for them to understand Venus’s rotation (Figure 10.16). Notice that the model
for the origin of Mercury’s massive iron core looks very much like the giant impact model
for the origin of the Moon (Figure 9.29). Given the wide ranges of mass ratios of impacting
body to planet, impact velocities, and impact parameter a wide variety of outcomes of the
impact is possible.
2. Venus
The Magellan images of Venus have been analyzed to produce three dimensional maps of
the surface of Venus. These, in turn, have been used as the basis of computer-generated
videos that simulate what could be seen if one could fly around and near various
atmospheric features. One of these videos is included in the CD that accompanies this
textbook.
KEY TERMS
arachnoid — A circular feature on the surface of Venus connected to other similar features by a
web of fractures.
corona — A circular feature on the surface of Venus. Coronae appear to be collapsed volcanic
domes and can be as much as several hundred kilometers across.
intercrater plain — Smooth portions of the surface of Mercury that lie between and around
clusters of large craters.
retrograde rotation — The westward rotation of a solar system body.
scarp — A cliff produced by vertical movement of a section of the crust of a planet or satellite.
shield volcano — A broad, gently sloped volcano built up by the repeated eruption of very fluid
lava.
smooth plain — Widespread sparsely cratered regions of the surface of Mercury possibly
having a volcanic origin.
ANSWERS TO QUESTIONS AND PROBLEMS
Conceptual Questions
1. Nights are 88 Earth days long and there is no atmosphere to insulate the surface.
2. The scarps probably formed when Mercury shrank in size after its surface hardened.
3. Because Mercury has a high density despite little internal compression
10-1
Chapter 10 - Mercury and Venus
4. The crater densities are similar, but material is thrown less far from craters on Mercury
because of the higher gravity of Mercury.
5. The cloud droplets mostly scatter (reflect) light rather than absorbing it, so after many
scatters some sunlight penetrates through the clouds.
6. The thick atmosphere of Venus (mostly CO2) is more effective than Earth’s in blocking the
escape of infrared radiation from the surface into space.
7. Red sunlight penetrates through the clouds more easily than blue sunlight, so everything
looks redder (orangeish) than it would in unfiltered sunlight.
8. The surface of Venus has a low crater density, probably because old craters have been
eradicated by
volcanic flows.
9. Mid-ocean ridges, trench systems, and mountain ranges should be visible.
10. Crustal deformation could have taken place through horizontal lifting and falling of parts of
the surface.
11. Earth’s carbon dioxide is mostly incorporated in carbonate minerals.
12. The higher temperature of the early Venus may have led to higher humidity so that
atmospheric water vapor produced a greenhouse effect. This may have raised temperature
and humidity and improved the greenhouse effect still further. Also, as oceans shrank,
carbon dioxide couldn’t be stored away in carbonate rocks and would have entered the
atmosphere to improve the greenhouse effect.
Problems
1. 1.5
2. 4 orbital periods
3. 1.6 years, it is the same length of time
Figure-Based Question
1. Both planets have broad plains (the ocean bottoms in the case of the Earth) and regions of
mountainous terrain; no mountain chains, long trenches, or oceanic ridge systems are found
on Venus; no circular chasms, such as the one on the southern edge of Aphrodite Terra, are
found on Earth.
10-2