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Earth and the Other Terrestrial Worlds © 2010 Pearson Education, Inc. What are terrestrial planets like on the inside? © 2010 Pearson Education, Inc. Earth’s Interior • Core: highest density; nickel and iron • Mantle: moderate density; silicon, oxygen, etc. • Crust: lowest density; granite, basalt, etc. © 2010 Pearson Education, Inc. Terrestrial Planet Interiors • Applying what we have learned about Earth’s interior to other planets tells us what their interiors are probably like. © 2010 Pearson Education, Inc. Role of Size • Smaller worlds cool off faster and harden earlier. • The Moon and (maybe) Mercury are now geologically “dead.” © 2010 Pearson Education, Inc. Surface Area–to–Volume Ratio • Heat content depends on volume. • Loss of heat through radiation depends on surface area. • Time to cool depends on surface area divided by volume: 2 p r 4 =3 Surface area–to–volume ratio = 4 pr 3 r 3 • Larger objects have a smaller ratio and cool more slowly. © 2010 Pearson Education, Inc. What processes shape planetary surfaces? © 2010 Pearson Education, Inc. Processes That Shape Surfaces • Impact cratering – Impacts by asteroids or comets • Volcanism – Eruption of molten rock onto surface • Tectonics – Disruption of a planet’s surface by internal stresses • Erosion – Surface changes made by wind, water, or ice © 2010 Pearson Education, Inc. Role of Planetary Size • Smaller worlds cool off faster and harden earlier. • Larger worlds remain warm inside, promoting volcanism and tectonics. • Larger worlds also have more erosion because their gravity retains an atmosphere. © 2010 Pearson Education, Inc. Role of Distance from Sun • Planets close to the Sun are too hot for rain, snow, ice and so have less erosion. • Hot planets have more difficulty retaining an atmosphere. • Planets far from the Sun are too cold for rain, limiting erosion. • Planets with liquid water have the most erosion. © 2010 Pearson Education, Inc. Role of Rotation • Planets with slower rotation have less weather, less erosion, and a weak magnetic field. • Planets with faster rotation have more weather, more erosion, and a stronger magnetic field. © 2010 Pearson Education, Inc. What are the major geological features of Mars? © 2010 Pearson Education, Inc. Volcanism on Mars • Mars has many large shield volcanoes. • Olympus Mons is largest volcano in solar system. © 2010 Pearson Education, Inc. What geological evidence tells us that water once flowed on Mars? © 2010 Pearson Education, Inc. Dry Riverbeds? • Close-up photos of Mars show what appear to be dried-up riverbeds. © 2010 Pearson Education, Inc. Erosion of Craters • Details of some craters suggest they were once filled with water. © 2010 Pearson Education, Inc. Crater Walls • Gullies on crater walls suggest occasional liquid water flows have happened less than a million years ago. © 2010 Pearson Education, Inc. What are the major geological features of Venus? © 2010 Pearson Education, Inc. Radar Mapping • Its thick atmosphere forces us to explore Venus’s surface through radar mapping. © 2010 Pearson Education, Inc. Cratering on Venus • Venus has impact craters, but fewer than the Moon, Mercury, or Mars. © 2010 Pearson Education, Inc. Volcanoes on Venus • It has many volcanoes, including both shield volcanoes and stratovolcanoes. © 2010 Pearson Education, Inc. Erosion on Venus • Photos of rocks taken by landers show little erosion. © 2010 Pearson Education, Inc. What is an atmosphere? An atmosphere is a layer of gas that surrounds a world. © 2010 Pearson Education, Inc. Earth’s Atmosphere • About 10 kilometers thick • Consists mostly of molecular nitrogen (N2) and oxygen (O2). © 2010 Pearson Education, Inc. Atmospheric Pressure Gas pressure depends on both density and temperature. © 2010 Pearson Education, Inc. Adding air molecules increases the pressure in a balloon. Heating the air also increases the pressure. Where does an atmosphere end? • There is no clear upper boundary. • Most of Earth’s gas is less than 10 kilometers from surface, but a small fraction extends to more than 100 kilometers. • Altitudes less more than 60 kilometers are considered “space.” © 2010 Pearson Education, Inc. Effects of Atmospheres • They create pressure that determines whether liquid water can exist on surface. • They absorb and scatter light. • They create wind, weather, and climate. • They interact with the solar wind to create a magnetosphere. • They can make planetary surfaces warmer through the greenhouse effect. © 2010 Pearson Education, Inc. How does the greenhouse effect warm a planet? © 2010 Pearson Education, Inc. Greenhouse Effect • Visible light passes through the atmosphere and warms a planet’s surface. • The atmosphere absorbs infrared light from the surface, trapping heat. © 2010 Pearson Education, Inc. “No Greenhouse” Temperatures • Venus would be 510°C colder without greenhouse effect. • Earth would be 31°C colder (below freezing on average). © 2010 Pearson Education, Inc. Why the Sky Is Blue • Atmosphere scatters blue light from Sun, making it appear to come from different directions. • Sunsets are red because red light scatters less. © 2010 Pearson Education, Inc. Earth’s Magnetosphere • Magnetic field of Earth’s atmosphere protects us from charged particles streaming from Sun (the solar wind). © 2010 Pearson Education, Inc. Aurora • Charged particles from solar wind energize the upper atmosphere near magnetic poles, causing an aurora. © 2010 Pearson Education, Inc. Sources of Gas Outgassing from volcanoes © 2010 Pearson Education, Inc. Evaporation of surface liquid; sublimation of surface ice Impacts of particles and photons Losses of Gas Thermal escape of atoms Condensation onto surface © 2010 Pearson Education, Inc. Sweeping by solar wind Chemical reactions with surface Large impacts blasting gas into space What is Mars like today? © 2010 Pearson Education, Inc. Seasons on Mars • The ellipticity of Mars’s orbit makes seasons more extreme in the southern hemisphere. © 2010 Pearson Education, Inc. Polar Ice Caps of Mars Late winter Mid-spring Early summer • Carbon dioxide ice of polar cap sublimates as summer approaches and condenses at opposite pole. © 2010 Pearson Education, Inc. Polar Ice Caps of Mars • Residual ice of the polar cap remaining during summer is primarily water ice. © 2010 Pearson Education, Inc. Dust Storms on Mars • Seasonal winds can drive dust storms on Mars. • Dust in the atmosphere absorbs blue light, sometimes making the sky look brownish-pink. © 2010 Pearson Education, Inc. What is Venus like today? © 2010 Pearson Education, Inc. Greenhouse Effect on Venus • Thick carbon dioxide atmosphere produces an extremely strong greenhouse effect. • Earth escapes this fate because most of its carbon and water is in rocks and oceans. © 2010 Pearson Education, Inc. Runaway Greenhouse Effect • A runaway greenhouse effect would account for why Venus has so little water. © 2010 Pearson Education, Inc.