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The Moon Astronomy 311 Professor Lee Carkner Lecture 13
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Which of the following was not a constituent of the Earth’s original atmosphere? a)Water b)Carbon Dioxide c)Ammonia d)Methane e)Sulfur Dioxide
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Why do we think the Earth’s core is liquid? a)Iron is always liquid at high pressures b)Since Venus and Mars have liquid cores, Earth should have one too c)Shear waves cannot penetrate the core d)Pressure waves cannot penetrate the core e)From computer modeling of convection
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What defines the outer edge of the habitable zone? a)Where planets are too small to have plate tectonics b)Where it is too cold for volcanism c)Where oxygen is no longer present in the atmosphere d)Where CO 2 clouds block out sunlight e)Where there are not enough icy planetesimals
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The mantle, outer core and inner core are, a)Solid, liquid, solid b)Liquid, solid, solid c)Liquid, solid, liquid d)Solid all the way down e)Liquid all the way down
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Temperature of Earth Temp of Earth from energy balance T E = [R S /(2 D S )] ½ T S T E = [6.96X108 / (2)(1.496X1011)] ½ (5778) T E = 278.7 K T F = 1.8T K -460 = (1.8)(278.7)-460 T F = 41.6 F Actual Earth temp = 288 K T = (1.8)(288)-460 = 58.4 F How much energy does Earth emit? P = AT 4 = 4 R E 2 T 4 P = (5.67X10 -8 )(4 )(6.38X10 6 ) 2 (288) 4 P = 1.995X10 17 W
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Luna -- The Goddess of the Moon Since ancient times the Moon has been thought to affect behavior (“lunatic”, “moonstruck”) There is no good evidence for this however
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Principle Features of the Moon Maria maria is Latin for seas arrangement of maria produces the “man-in-the- moon” Highlands Craters circular impact structures range in size from few hundred km to microscopic
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Moon Facts Size: 3476 km diameter Orbit: 384,000 km Description: small, airless, cratered surface is similar to Mercury
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Timeline of Moon Exploration Luna 1 (USSR, 1959) first spacecraft to fly by the Moon Luna 2 (USSR, 1959) Luna 9 (USSR, 1966) first lunar lander Luna 10 (USSR, 1966) Apollo 8 (USA, 1968) first manned orbiter Apollo 11 (USA, 1969) Luna 16 (USSR), 1970) first automated sample return
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Near and Far Sides of the Moon
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Why is the Moon Airless? Gravity Thermal motions All molecules have a velocity proportional to their temperature The Moon has no atmosphere because this velocity is too large for its gravity to overcome
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The Surface of the Moon Maria: covered with dark colored mare basalt similar to lava on Earth Highlands: covered with light colored anorthosite very old (more than 4 billion years) Moon rocks are similar in many ways to Earth rocks, but are depleted in volatiles
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Mare Basalt and Anorthosite
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Tycho and Rays
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Falling Bodies Real impactors get their energy from their very high orbital velocities A body a height h above a surface has potential energy: PE = mgh 1000 grams = 1 kg g = 9.8 m/s 2 h is the height above the surface in meters
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Energy When the object hits the surface, all of the potential energy is converted into kinetic energy: PE = KE = ½mv 2 PE = KE mgh = ½mv 2 v = (2gh) ½ If g and h are in meters, v is in m/s
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The Moon’s Interior Moon is much less active than the Earth Moon is much less dense than the Earth Moon once had a magnetic field but does not today, indicating that the core has solidified
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Inside The Moon
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Moon Formation Theories
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Collisional Ejection Theory The collision put large amounts of debris in orbit, which formed into the Moon Energy from impact depleted the Moon in volatiles The ejected material was mostly mantle rock, so the Moon has a very small core
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A History of the Moon 4.6 billion years ago: 4.6-3.8 billion years ago: ~3.8 billion years ago: large impacts produce mare basins 3.8-3.1 billion years ago: 3 billion years ago- present core solidified, no more magnetic field small amounts of cratering
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Next Time Read Chapter 10
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Summary Moon was formed 4.6 billion years ago when large impactor hit the Earth Moon has a low density because it has only a small iron core Moon has become tidally lock so that only the near-side faces Earth Most of our information about the Moon comes from the Apollo missions
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Summary: Surface Maria large impacts produced basins which then filled with lava darker, denser and younger than the highlands Highlands regions that have not experienced large impacts or lava lighter, less dense and older than the Maria Large numbers of impacts have covered the surface with craters and regolith (dust)
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