AS101 Lecture 20

AS101 Lecture 20 - AS101 Lecture 20 Logistics: Midterm 2:...

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AS101 Lecture 20 Logistics: • Midterm 2: Nov 18 – same format Covers Chapters 5 – 9 BRING CALCULATORS Last Lecture: • Geology of Terrestrial Planets Today’s Lecture: • Atmosphere of terrestrial planets
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What is an atmosphere? An atmosphere is a layer of gas that surrounds a world
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Atmosphere of Terrestrial worlds Atmospheres on Terrestrial planets are more varied than their geology • Moon and Mercury has no atmosphere but Venus, Earth and Mars do Atmospheres play a major role in defining planetary geology • Venus, Earth and Mars are essentially at the same distance from the Sun, but Venus is very hot, Earth is temperate and Mars is dry, barren and cold
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Atmosphere Atmosphere depends on • Surface temperature which depends on distance from the Sun Atmosphere • Gravity, which depends on size • Rotation rate • Composition
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Effects of an Atmosphere on a Planet creates pressure • allows water to exist as a liquid creates wind and weather • promotes erosion of planetary surfaces scattering and absorption of light absorbs high-energy radiation scatters optical light (brightens the daytime sky) greenhouse effect warms the planetary surface Enables living creatures to leave ocean Note: Atmospheres are thin!
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Comparing Terrestrial Atmospheres Andrew Kuhn : Where is the Earth’s Carbon Dioxide on the list?
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Where does an atmosphere end? Small amounts of gas are present even at > 300 km
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Earth’s Atmosphere About 10 km thick Consists mostly of molecular nitrogen (N 2 ) and oxygen (O 2 )
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Where does the atmosphere end? Not an easy thing to define We say that Mercury and Moon has no atmosphere, but strictly speaking they do If we use the criteria that atmosphere ends where one sees stars during daytime, to be the edge of the atmosphere, then, atmosphere ends around 50 km (round number)
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<- The sky is black here. At this height, we should see stars during daytime. This picture of the
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This note was uploaded on 04/14/2011 for the course ASTRO 101 taught by Professor Oppenheim during the Spring '11 term at BU.

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AS101 Lecture 20 - AS101 Lecture 20 Logistics: Midterm 2:...

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