AST 251 Lecture 12

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Astronomy & Astrophysics

AST 251 Lecture 12Rare Earth Hypothesis o Most scientists expect large numbers of terrestrial size planets with conditions sufficiently similar to Earth to lead to life formation o Hypothesis states that Life similar to that on Earth is extraordinarily rare and couldve happened only through a very unusual set of fortunate circumstances o Usually it is agreed that simple forms of life may relatively easily form but the higher level life would exist on Earth through incredible luckArguments o Galactic HZEarthlike planets can form in certain parts of the Galaxy If too far from the centre then too little heavy elementsIf too close to the centre then too many devastating Supernova explosions that would destroy lifeBut recent theoretical calculations show that stars change distance to galactic center o Earth is special in having plate tectonics which enable CO cycle to operate and 2hence ensures the climate stabilityBut dont know how common plate tectonics is in Earthsized planets o The role of Jupiter in deflecting and swallowing comets and planetoids which otherwise would strike the Earthif the Solar System had a hot Jupiter close to the Sun there would be no defense against themYes but dont know how common hot Jupiters are recall biases in ET planet detections o There is just right amount of water on EarthBut life on Earth is very adaptable as long as there is some water o Earth has a big Moon which prevent it to experience chaotic and unpredictable rotation axis tilt variation such as Marsonly thanks to the Moon was Earths climate stable enough for a long timeBut dont know how common big moons are o Several lesser argumentsWhat if Earth experienced different collisionsWhat if the Snowball Earth episodes did not take placeWhy was the Cambrian explosion so special and so unique If it did not happen what thenDrakes Equation o Attempts to estimate the number of currently living inhabited communicating civilizations in the Galaxy o 1961 Drake wrote this equationRhow many stars are being born per year in our galaxy
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