After
Completing These Learning Activities You Should Be Able To:
After
Completing These Learning Activities You Should Be Able To:
Read
This Material in Your
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Read
These Notes:
Figure 1: 29 KB
Four factors seem to be significant in the evolution of a planet's atmosphere.
These factors are:
Distance from Sun::The distance of a planet from the sun is the most important factor. First, it determines how much energy the atmospheric gases receive from the Sun. That determines the temperature of the atmospheric gases. The temperature of the gases is a measure of how fast the atoms or molecules are moving (kinetic energy (def.). The relationship between temperature and kinetic energy is direct. The greater the kinetic energy, the more likely that atmospheric gases will reach escape velocity (def.). Thus, terrestrial planets are more likely than jovian planets to have atmospheric gases escape.
Second, distance from the Sun is important because planets closer to the Sun would be most affected by the T-Tauri winds which are thought to have swept the lighter gases out of the inner Solar system. Also, the gravitational effects of the Sun would cause most of the hydrogen and helium near the Sun to be swept up by the Sun, leaving little behind for the planets close to it.
Mass of the Planet:: The mass of the planet is directly related to its escape velocity. Therefore low mass planets such as the terrestrials have low escape velocities . This makes it easier for atmospheric gases to escape these planets. The jovians, on the other hand, have high escape velocities because of their high masses. This makes it more difficult for jovian planets to lose atmospheric gases.
When the energy from the Sun strikes the atmospheric gases of a planet, the energy is transferred to the molecules and their kinetic energy increases. The amount by which their energy is increased is inversely related to their masses. Thus the same amount of energy transferred to a light molecule will cause it to accelerate more than when the same amount of energy is transferred to a heavy molecule. Thus the light molecule will more readily escape. This explains while the lighter gases, hydrogen and helium escaped from the inner part of the solar system where temperatures were highest.
The presence of abundant liquid water: The presence of oceans of water seems to explain the uniqueness of the Earth's atmosphere. Whether water can exist as a liquid is determined by the temperature of the planet and atmospheric pressure at its surface. The 900 degree temperatures at the surface of Venus prevents water from existing either as a solid or as a liquid. In fact conditions are such that even water vapor is quickly dissociated. On Mars temperatures and atmospheric pressure is such that water can exist in the frozen and gaseous state, but no in the liquid state. According to our present theories, the Earth's vast oceans serve as one of three sinks (def.) by which large quantities of carbon dioxide are dissolved.
Complete
These Self-check
Questions: These questions and their
answers are designed to help you determine how well you understand this objective
and to provide additional instruction.
Homework
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in the text. Complete the self-check questions before attempting the homework.
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