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15-Venus_Mars - Venus VenusandMars DeathbyFireor DeathbyIce...

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Venus and Mars Death by Fire or Death b Ice Death by Ice Biology 190A Lecture 15
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The Outer Limits “Oort cloud” reaches more than 100 000 AU of the Solar System more than 100,000 AU from the Sun—and perhaps contains more mass than the Earth The objects may have formed near the giant planets and then were tossed outwards by gravitational encounters Passing stars or other gravitational influences d h nudge the comets into the inner Solar System
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Comet Nuclei A few probes have visited comet nuclei They contain ices A few probes have visited comet nuclei. They contain ices and dust, venting gas where the Sun heats them. Since comets spend most of their lives in a remote deep freeze, they indicate the Solar System’s original composition. Comet Halley, visited by Giotto Comet Wild 2, visited by Stardust
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Comets As a comet moves into the inner solar system it is As a comet moves into the inner solar system, it is warmed by the Sun. They may even have delivered water to Earth in its early history water to Earth in its early history. Ices on the surface sublimate (go from solid to gas) and stream away from the comet nucleus also and stream away from the comet nucleus, also carrying away dust particles. The gas and dust are pushed by the solar wind and radiation pressure, making “tails” that point away from the Sun.
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The Inner Solar System Bodies that look similar in many t ways to Earth, but with distinct differences.
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The Effects of a Planet’s Mass and Radius Small planets cool quickly leading to little tectonic Small planets cool quickly, leading to little tectonic activity or outgasing from molten rock. Atmospheres “leak away” to space faster if the surface Atmospheres leak away to space faster if the surface gravity is weaker. Without an atmosphere, the Moon and Mercury also have little erosion. Some features on Mercury and Mars’s volcanoes, imply some past geological activity perhaps until a few some past geological activity, perhaps until a few hundred million years ago on Mars.
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The Evolutionary Stages of Planets All of the terrestrial planets were more similar when born. Larger planets cool off more slowly, so even if born at the same time, they are generally in an earlier stage.
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Atmospheres of the Terrestrial Planets All of the planets had comets impacting them and molten material outgasing when they were young Why is Earth’s atmosphere so much less massive than Why is Earth s atmosphere so much less massive than Venus’s today?
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