AST-L10-ch6__3

AST-L10-ch6__3 - AST 1002"Terrestrial Planets Atmospheres...

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1 Today’s Lecture: purpose & goals AST 1002 Planets, Stars and Galaxies Terrestrial Planets: Atmospheres “Comparative Planetology -- learn by comparing planet’s properties; Understand the concepts of: 1) PlanetaryAtmospheres 2) Greenhouse Effect 3) Atmospheric Loss 4) Planets: Mercury, Venus, Mars, Moon Review Fact vs. Theory Inner Planets Planet interiors Density r = M/V Differentiation – denser material sinks to center, lighter material floats to top Largest planets cool slowest. Magnetic fields caused by flow of electric charges in liquid metal interior Four Main Processes Impact Cratering Volcanism Tectonics Gradation Blue Skies & Beautiful Sunsets What makes them so? Blue Skies Nitrogen and small particulates scatter blue light in all directions across the sky, but leaves the redder light largely unaffected. Beautiful Sunsets Blue light is removed as it travels a long distance through the atmosphere. When the Sun is low in the sky, and less bright, we see the residual red light that comes straight at us .
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2 Reminder: Temperature In science temperature is measured in Kelvin (K) The scale starts at the lowest possible temperature , called absolute zero 0 0 C (ice freezes) corresponds to 273 K 27 0 C (room Temperature) corresponds to 300 K 100 0 C (water boils) corresponds to 373 K Temperatures involved in astronomical processes range from ~ 3K to several billion K Atmospheres Energies of Gas Molecules Kinetic energy of any object in motion is K.E. = ½ mv 2 ( m = mass, v = speed) The average kinetic energy per gas molecule is 3 / 2 kT k = 1.381x10 -23 J/K is Boltzman’s constant T is the absolute temperature in Kelvin Consist of atoms and molecules moving about in random directions, that is, gases . Pressure Is the force per unit area. It arises from collisions between the atoms and molecules Temperature Is a measure of the average kinetic energy of the particles, that is, the energy of motion. Atmospheric Gases – Some Basics Lighter gases rise This is really because heavier gases sink and push the lighter gases upward Sunlight and heat from a planet’s interior provide energy to heat atmospheres Sunlight can also break up molecules ideal gas box kT mv 2 3 2 2 1 = m kT v 3 = avg What i s the s peed of ga s mo l e c u l e s ? Equate the formula for kinetic energy to that for the average kinetic energy per molecule Example: At T = 300 K oxygen molecules move at an average of ~ 500 m/s , hydrogen molecules at ~ 1950 m/s But there is a distribution of speeds. Some of the molecules move much faster than the average.
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