Transcript 25drake3s
Extra-Terrestrial Life and the Drake Equation Astronomy 311 Professor Lee Carkner Lecture 26 Observing Project Due Friday Project should be neat, organized, labeled and have all questions fully answered Telescope objects: Venus, Uranus, Neptune, Saturn, Moon We will try for the Sun on Friday Meet in planetarium We will try to observe tonight at 9pm Check web page Is There Anybody Out There? People have long speculated about life on other worlds Modern observations indicate that the solar system is uninhabited How can we estimate the possibility of extraterrestrial life? The Drake Equation In 1961, astronomer Frank Drake developed a formula to predict the number of intelligent species in our galaxy that we could communicate with right now Solving the Drake equation helps us to think about the important factors for intelligent life The Drake Equation N=R* X fp X ne X fl X fi X fc X fL N = The number of civilizations in the galaxy R* = Number of stars in the galaxy fp = Fraction of stars with planets ne = Average number of suitable planets per star fl = Fraction of suitable planets on which life evolves fi = Fraction on which intelligence develops fc = Fraction that can communicate fL = Lifetime of civilization / Lifetime of star The Milky Way R* -- Stars We start with the number of stars in the galaxy We are ruling out life around neutron stars or white dwarfs or in non-planetary settings (nebulae, smoke rings, etc.) The H-R Diagram The Orion Star Forming Region Protoplanetary Disk in Orion Extra-Solar Planets fp -- Planets Very high mass stars go supernova before planets can form Need medium mass stars (stars like the Sun) fp -- Finding Planets Studies of star forming regions reveal that circumstellar disks are common around young stars Only about 75 have been found, but we can only find the most obvious ones The Carbonate-Silicate Cycle Atmosphere Water + CO2 (rain) CO2 Volcano CO2 + silicate (subvective melting) Ocean Carbonate + silicate (Sea floor rock) Carbonate + water (stream) Venus Mars ne -- Suitable Planets What makes a planet suitable? Must be in habitable zone Heat may also come from another source like tidal heating (Europa) ne -- Unsuitable Planets The Moon -Mars -Jupiter -Venus -- Earth at 2 AU -- CO2 builds up to try and warm planet, clouds form, block sunlight The Miller-Urey Experiment Comet fl -- Life The building blocks of life on Earth are organic compounds The Miller-Urey experiment demonstrates that organic material could have formed from the material available on the early Earth The KT Impact fi -- Intelligence Life alone is not sufficient, intelligence is needed to communicate Many things could interfere with evolution in this time Life on Earth has gone through many disasters (e.g. mass extinctions), but has survived Europa fc -- Communication Even intelligent life may not be able to communicate What could keep intelligent life from building radio telescopes? O’Neill Colony O’Neill Colony -- Interior fL -- Lifetime fL = Lifetime of civilization / Lifetime of star How long does a civilization last for? fL -- Destroying Civilization What could destroy a civilization? Space colonization greatly reduces risk or extinction The Fermi Paradox Physicist Enrico Fermi asked, “If there are many civilizations in the galaxy why haven’t they contacted us?” Cosmic Zoo -Berserker Theory -The Gibson Continuum -- The Von Neumann Problem Build a self replicating space probe (a Von Neumann machine) Even if it takes 100,000 years to get to the next star and 1000 years to make a copy, in 100 million years the galaxy is full of machines Summary: Life in the Galaxy Medium size, medium luminosity star with a planetary system A planet of moderate mass in the habitable zone Organic compounds reacting to form simple life Life evolving over billions of years with no unrecoverable catastrophe Intelligent life building and using radio telescopes A long lived civilization