Lecture 22

Is There Other Intelligent Life in the Universe - and can we find it?

The Drake Equation

To read an interview with Frank Drake, click here.

To make your own estimate of the probability of other intelligent life using the Drake equation, click here.

• many uncertainties associated with terms in equation (some terms are more uncertain than others -- which ones and why?)
  • one possibility is Earth harbors the only intelligent, communicative organisms in Galaxy

  • OR a few (relatively) short-lived technological civilizations are scattered far apart among stars, never contacting each other before disappearing

  • OR there is a large number of life-bearing planets

  • estimates of number of other intelligent civilizations range from 0 to 10 trillion!!!

• development of astrobiology
  • convergence of wide range of scientific disciplines

  • astronomy, biology, paleontology, oceanography, microbiology, geology, and genetics, among others

  • consideration of entire planets as ecological systems

  • life on Earth considered only single example of how life might work, rather than only example

• suggestions of simple life on Mars and undersea life on Europa...

  • Galileo spacecraft took measurements of Europa's magnetic field during January 2000 flyby 218 miles above this moon of Jupiter

  • magnetic north pole reverses every 5 1/2 hours (something that would make a compass difficult to use!)

  • underground layer of conductive liquid -- like saltwater -- best explains the magnetic flip-flop

  • Europa has cracked, icy surface, suggesting floating, colliding ice on liquid ocean

• coupled with discoveries of extrasolar planets and extremophiles...

  

  

• make some people think that latter possibilities are more likely (fl and fp terms might be large ---> N large)

What about Uncertainties in the Drake Equation?

• recently, values of ne, fi have been hotly debated

• evidence that bacteria did not give rise to animals in steady progression
  • there were many fits and starts, experiments and failures

  • life may have evolved early in Earth's history (as soon as it possibly could have), even under conditions of great heat, pressure, and lack of oxygen, just like conditions in a lot of the Universe!

  • BUT formation of animal life much more recent and protracted

• furthermore, attaining stage of animal life is one thing, maintaining that level is another

• Rare Earth hypothesis (Ward and Brownlee) -- planets like Earth are very unusual, opposite of Copernican trend!
  • for example, Earth has been orbiting a star with relatively constant energy output for billions of years

  • although life may exist on even harshest of planets and moons, animal life needs more benign conditions and those conditions must be stable for great lengths of time

  • animals as we know them require oxygen, yet it took 2 billion years for enough oxygen to be produced to allow animals on Earth to flourish

  • our planet was also of suitable size, chemical composition, and distance from Sun to enable life to thrive ---> water in liquid state

  • relatively low asteroid or comet impact rate on Earth (Jupiter probably acted as ``comet and asteroid catcher'' and how common are Jupiter-sized planets?)

    

  • Earth only planet with Moon of such appreciable size and proximity ---> keeps the Earth's tilt stable (and therefore stabilizes the climate)

  • plate tectonics (and thus continental drift) enables a global thermostat to exist

    

  • Earth lies in Solar System far from Galactic center

    

    • perhaps supernovae and close stellar encounters preclude long, stable conditions on more central planets

    • outer regions of galaxies may have too low a percentage of heavy elements necessary to build rocky planets and to fuel radioactive warmth of planetary interiors

    • comet influx rate may be affected

    Given all this information, now try to estimate the number of intelligent civilizations in the Galaxy from the Drake equation.

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