ASTR 100Lgx Lecture Notes - Lecture 16: The Moons, Doppler Spectroscopy, Escape Velocity
Document Summary
Earth has little free hydrogen because it can achieve escape velocity easily. All planets have escape velocities depending on the strength of their gravity. If a planet"s escape speed is 5 times the average speed of its molecules, you"ll have an atmosphere for at least 5 billion years. There are two main theories, evolutionary and catastrophic. Volatile elements are gases at relatively low temperatures. Descarte proposed the whirlpool or vortex theory in 1644. An unusual incident created the solar system, like the collision of the sun and another star. First proposed by buffon in 1745 that a comet pulled material away. Planetary systems are too common for star collisions to cause them. Carl von weizsacker 1940 showed that eddies would form in a rotating gas cloud. An object shrinking from gravity heats up, forming the protosun. Magnetic braking can account for the slow rotation of the sun. Nonvolatile elements would end up near the sun, thusly terrestrial planets.
