Chapter 18 The Search for Extra-terrestrial Life

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Chapter 18 The Search for Extra-terrestrial Life
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What do you think?

• What do people who search for extraterrestrial
  intelligence look for?

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Our planet is special to us, but is not unique in
its possibilities for life

• What are the elements necessary for life?
• C A R B O N
• organic molecules that have carbon and ...
• hydrogen
• nitrogen
• oxygen
• sulfur
• phosphorus

• ethyl alcohol
• formaldehyde
• methyl cyanoacetylene
• acetaldehyde

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Miller-Urey Experimentshowed that numerous
organic compound necessary for life can be
synthesized from gases present in Earths early
atmosphere.
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SETI uses radio telescopes to eavesdrop on
radio/TV communications from other civilizations

• SETI - Search for Extraterrestrial Intelligence
• High Resolution Microwave Background Survey
• Now, primarily funded through private donations

• Radio waves travel at the speed of light

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THE WATER HOLE The Best Place to Listen
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The Drake equation predicts how many
civilizations are in the Milky Way

• N RfpneflfifcL
• R rate at which solar-type stars form in the
  galaxy
• fp fraction of stars that have planets
• ne number of planets per stay system suitable
  for life
• fl fraction of those habitable planets on
  which life actually arises
• fi fraction of those life forms that evolve
  into intelligent species
• fc fraction of those species that develop
  adequate technology and then choose to send
  messages out into space
• L lifetime of that technologically advanced
  civilization

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We have been sending signals and spaceprobes into
space for a century

• TV signals broadcast since the 1930s
• Frank Drake sent a message directed at the great
  globular cluster in Hercules which is 30,000
  light years away
• Voyager spacecraft now leaving our solar system
  launched in the 1980s carry human memorabilia

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Plaque on Voyager Space Probes
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What did you think?

• What do people who search for extraterrestrial
  intelligence look for?
• They search for radio signals from other advanced
  civilizations.

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Self-Check

• 1 Discuss the Drake Equation and make estimates
  for the various factors in it.
• 2 Explain why radio telescopes are used in the
  search for extraterrestrial signals.
• 3 Outline the results to date of the SETI
  program.