1. Extra-Terrestrial Life and the Drake Equation Astronomy 311 Professor Lee Carkner Lecture 26

2. 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

3. 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 extra- terrestrial life?

4. 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

5. The Drake Equation N=R * X f p X n e X f l X f i X f c X f L  N = The number of civilizations in the galaxy  R * = Number of stars in the galaxy  f p = Fraction of stars with planets  n e = Average number of suitable planets per star  f l = Fraction of suitable planets on which life evolves  f i = Fraction on which intelligence develops  f c = Fraction that can communicate  f L = Lifetime of civilization / Lifetime of star

6. The Milky Way

7. 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.)

8. The H-R Diagram

9. The Orion Star Forming Region

10. Protoplanetary Disk in Orion

11. Extra-Solar Planets

12. f p -- Planets  Very high mass stars go supernova before planets can form    Need medium mass stars (stars like the Sun) 

13. f p -- 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

14. The Carbonate-Silicate Cycle Water + CO 2 (rain) Ocean Carbonate + silicate (Sea floor rock) CO 2 Volcano Atmosphere Carbonate + water (stream) CO 2 + silicate (subvective melting)

15. Venus

16. Mars

17. n e -- Suitable Planets  What makes a planet suitable?   Must be in habitable zone    Heat may also come from another source like tidal heating (Europa)

18. n e -- Unsuitable Planets  The Moon --  Mars --  Jupiter --  Venus --  Earth at 2 AU -- CO 2 builds up to try and warm planet, clouds form, block sunlight

19. The Miller-Urey Experiment

20. Comet

21. f l -- 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 

22. The KT Impact

23. f i -- 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

24. Europa

25. f c -- Communication  Even intelligent life may not be able to communicate   What could keep intelligent life from building radio telescopes?     

26. O’Neill Colony

27. O’Neill Colony -- Interior

28. f L -- Lifetime  f L = Lifetime of civilization / Lifetime of star    How long does a civilization last for?

29. f L -- Destroying Civilization  What could destroy a civilization?      Space colonization greatly reduces risk or extinction

30. 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 --

31. 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 

32. 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