Chapter 29: Life in the Universe

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Chapter 29 Life in the Universe

• Does life exist beyond Earth?
• In our own solar system?
• Does intelligent life exist?
• How can we search for life?

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The Case for Life Beyond Earth

• There are billions of galaxies in the universe,
  and the typical galaxy contains billions of
  stars 1018 stars!
• Planets have been found around many nearby stars
  planet formation seems to be a natural result of
  star formation.
• Even if life is rare, there is a strong
  possibility that it occurred more than once.

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The Copernican Principle

• There is nothing special about our place in the
  universe
• Copernicus proposed a model for the solar system
  with planets orbiting the Sun.
• Later we discover that the Sun is not the center
  of the Milky Way, nor is the Milky Way the center
  of the universe.
• The atoms of which were made comprise just a
  fraction of the stuff of the universe.

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Astrobiology

• The study of the origin, distribution, and
  ultimate fate of life in the universe.
• Combines astronomers, biologists, chemists,
  geologists,

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How to Search for Life

• A basic search for life should include the
  simplest form of single celled life.
• Can we find some requirements for life that will
  narrow a search?
• Water (can something take its place?)
• Energy source light or chemical
• Chemistry organic compounds or alternate

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Organic Molecules

• Life on Earth is based on organic molecules
  carbon-based molecules with hydrogen, nitrogen,
  oxygen, or a few other elements.
• Organic molecules have been found in clouds of
  interstellar gas and dust!
• Starting from these organic molecules, chemists
  formed amino acids in a simple apparatus that
  mimics the conditions of Earth 4 billion years
  ago.

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Extremophiles

• Biologists have discovered that life can exist in
  rather extreme environments
• Hot springs where the water temperature is close
  to 100ºC.
• Frozen for thousands of years in Antarctic ice,
  and able to reanimate when thawed.
• Living without light near deep sea vents called
  black smokers.
• Living in high acidity environments like the Rio
  Tinto.

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Biomarkers

• To search for life around other stars, we should
  look for something distinctive of life
  biomarkers.
• The simultaneous presence of oxygen and methane
  is a clear biomarker.
• Unfortunately the Earth didnt have much free
  oxygen for much of the time that life existed.
• An indisputable signal is still being sought.

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Habitable Zone

• The Habitable zone is the region around a star
  where a planet with liquid water could exist.

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Could There Be Life on Mars?
Or Europa? Or Encelades?
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Intelligent Life

• Of course, electromagnetic signals from
  extra-terrestrial life would be a very clear
  signature.
• SETI Search for Extra-Terrestrial Intelligence
• Scientists scan many radio frequencies searching
  for non-random signals.
• The latest idea is to search for brief signals in
  visible light.

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Listening for Signals from Intelligent Life
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The Drake Equation

• Predicts number of civilizations we could
  detect signals from in galaxy, N
• R rate of star formation (about 10/year)
• fp fraction of stars with planets
• ne number of Earth-like planets / system
• fl fraction of them where life develops
• fi probability that intelligence evolves
• fc prob. that advanced civilization evolves
• L lifetime of advanced technology

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The Drake Equation

• If we take
• R 10/year
• fp 1.0
• ne 1.0
• fl 0.1
• fi 1.0
• fc 1.0
• then N L, or the number of detectable
  intelligent civilizations equals the length of
  time that such civilizations survive.
• Our civilization has been at this stage since
  about 1900, or 100 years.

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Sending Signals

• We have sent several space probes on voyages out
  of our solar system.
• These probes carry plaques with information about
  us, in case they are intercepted by other
  intelligent life.
• Kind of like a note in a bottle.

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Discussion Question

• Should we actively try to send signals to any
  extra-terrestrial life that may be out there?
  Please consider what the consequences could be.