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Unformatted text preview: 1 Extraterrestrial Life: Spring 2008 Extraterrestrial Life: Lecture #6 What are the requirements for the Earth (or another planet) to be habitable? • liquid water on surface • atmosphere • plate tectonics / volcanism • magnetic Feld • … Extraterrestrial Life: Spring 2008 Liquid water is important because: • solvent for organic molecules • allows transport of chemicals within cells • involved in many biologically important chemical reactions Other solvents (ammonia, methane etc) exist in liquid form on planets but are much less promising for life Normal atmospheric pressure: liquid water requires: o C (273K) < T < 100 o C (373K) …require planets with surface temperatures in this range Extraterrestrial Life: Spring 2008 What determines the Earth ’ s surface temperature? incident Solar radiation fraction of incident radiation is re¡ected remainder is absorbed by the Earth and then reradiated If the Earth is not heating up or cooling down, the total of incoming and outgoing radiation must balance Are there other sources of energy for a planet? Extraterrestrial Life: Spring 2008 Solar constant The Fux of energy is the amount of energy that passes through unit area (1 m 2 ) in one second Measured in units of watts / m 2 Solar ¡ux declines with distance as 1 / d 2 : flux = L 4...
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- Spring '08
- Planet, Extraterrestrial life