lecture18spring2009 - Astronomy100Dr.Rhodes Lecture Chapter...

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Astronomy 100 - Dr. Rhodes Lecture #18 - 2/27/2009
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Chapter 8: The Terrestrial Planets Venus Hypothesis for Venus/Earth Differences Venus’s higher surface temperature (due to its formation somewhat closer to the Sun) created a run-away greenhouse effect. Water did not condense out of its atmosphere into oceans that could absorb CO 2 (as happened on Earth). Instead, most of the CO 2 remained in the atmosphere where it trapped much of Venus’s own infrared (“heat”) radiation, which lead to thick clouds and very high temperatures.
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Chapter 8: The Terrestrial Planets Venus Venus became hotter, and this heat then baked more CO 2 out of the surface rocks. Finally, an equilibrium was reached between the infrared radiation reflected back from the clouds and that reemitted into space. The extremely high-temperature conditions on Venus today are entirely due to the trapped infrared radiation from its surface. We do not want even a moderate run-away greenhouse effect to occur here on Earth.
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Chapter 8: The Terrestrial Planets Venus Earth’s temperature is elevated about 35 Celsius degrees (63 Fahrenheit degrees) by the natural greenhouse effect. For the past 150 years humans have been injecting at an ever increasing rate CO 2 and other greenhouse-causing chemicals into the atmosphere. Some studies indicate that doubling the CO 2 in the atmosphere could increase Earth’s average temperature between 2.8°C (5.0°F) and 5.2°C (9.4°F).
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Chapter 8: The Terrestrial Planets Venus Plant growth naturally decreases atmospheric CO 2 . Unfortunately, we are destroying tropical forests at the rate of 1 acre per second. Hence, we are eliminating a natural means of controlling the amount of CO 2 in the atmosphere. So much solar radiation is reflected from Venus’s clouds that if Venus had no greenhouse effect, its atmosphere would be cooler than Earth’s.
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Chapter 8: The Terrestrial Planets Mars Mars as Seen from Earth Mars is the only planet with surface features that can be seen from Earth.
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