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Extra-Terrestrial Life and the Drake Equation

Extra-Terrestrial Life and the Drake Equation. Astronomy 311 Professor Lee Carkner Lecture 25. Is There Anybody Out There?. People have long speculated about life on other worlds Modern observations indicate that the solar system is uninhabited

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Extra-Terrestrial Life and the Drake Equation

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  1. Extra-Terrestrial Life and the Drake Equation Astronomy 311 Professor Lee Carkner Lecture 25

  2. Is There Anybody Out There? • People have long speculated about life on other worlds • Modern observations indicate that the solar system is uninhabited • These searches have only covered a tiny part of the galaxy, however • How can we estimate the possibility of extra-terrestrial life?

  3. 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 • No one agrees on what the right values are • Solving the Drake equation helps us to think about the important factors for intelligent life

  4. The Drake Equation N=R* X fp X ne X fl X fi X fc X fL • N = • R* = Number of stars in the galaxy • fp = • ne = Average number of suitable planets per star • fl = Fraction of suitable planets on which life evolves • fi = • fc = Fraction that can communicate • fL = Lifetime of civilization / Lifetime of star

  5. The Milky Way

  6. 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.)

  7. The H-R Diagram

  8. The Orion Star Forming Region

  9. Protoplanetary Disk in Orion

  10. Extra-Solar Planets

  11. fp -- Planets • What kind of stars do we need? • High mass stars may become a giant before intelligent life can develop • Need medium mass stars (stars like the Sun) • Can we find planets? • Circumstellar disks that produce planets are common • We have just begun the search for planets

  12. The Carbonate-Silicate Cycle Atmosphere Water + CO2 (rain) CO2 Volcano Ocean CO2 + silicate (subvective melting) Carbonate + water (stream) Carbonate + silicate (Sea floor rock)

  13. Venus

  14. Mars

  15. ne -- Suitable Planets • What makes a planet suitable? • Must be in habitable zone • 0.95-1.37 AU for the Sun • Heat may also come from another source like tidal heating (Europa)

  16. ne -- Unsuitable Planets • The Moon -- Too small to have an atmosphere • Mars -- • Jupiter -- Too large, has no surface • Venus -- • Earth at 2 AU -- CO2 builds up to try and warm planet, clouds form, block sunlight

  17. The Miller-Urey Experiment

  18. Comet

  19. fl -- Life • Complex molecules containing carbon, (e.g. proteins and amino acids) • Organic material is also found in carbonaceous chondrites and comets

  20. The KT Impact

  21. 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

  22. Water Worlds - Intelligent Life?

  23. Europa

  24. fc -- Communication • Even intelligent life may not be able to communicate • What could keep intelligent life from building radio telescopes? • Waterworld (can’t smelt metals underwater) • Wrong biology (no hands, no eyes, etc.) • Lack of curiosity or resources

  25. O’Neill Colony

  26. O’Neill Colony -- Interior

  27. fL -- Lifetime • fL = Lifetime of civilization / Lifetime of star • Beginning of civilization defined as when radio telescopes are invented

  28. fL -- Destroying Civilization • What could destroy a civilization? • Nuclear or biological war • Impact • Civilization may be able to rebuild

  29. N • Multiply these factors together to get N • The number of intelligent civilizations in our galaxy that we could communicate with right now • If you evenly distribute the civilizations across the galaxy, how close is the nearest one? • N ~ 1 • N ~ 10 D ~ • N ~ 1000 D ~ • N ~ 100,000 D ~ • N ~10,000,000 D ~

  30. 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

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