Life In Our Solar System

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Life In Our Solar System

• LAWKI Life As We Know It
• Carbon Based organic compounds contain Carbon
  atoms.
• Water a basic requirement for chemical
  reactions, also used to transport nutrients
  waste.
• Possible locations for life elsewhere in our
  Solar System
• Europa Liquid-water ocean beneath an icy crust.
  Probably not stable enough to allow life to
  evolve over billions of years.
• Titan Sunlight methane create organic smog
  particles on surface. Unfortunately,
  temperatures too low for chemical reactions to
  happen quickly enough.
• Mars best chance for finding life. So far, no
  current life has been detected (but previous life
  is debatable).

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Life In Other Planetary Systems

• Extra-solar planets have been found around many
  stars. Therefore, planetary systems appear to be
  common.
• Planets suitable for life need stable orbits
  (around single stars?)
• Roughly ½ - 2/3 of all stars form in binary
  pairs.
• Can they form planets with stable orbits? Yes!
• Case 1 Planet orbits close to one of the stars.
• Case 2 Planet orbits far from both stars.
• Case 3 Planet switches back and forth.
• Will these planets be habitable? Probably not.
• Case 1 Planet will be too hot for liquid water.
• Case 2 Planet will be too cold for liquid
  water.
• Case 3 Temperature will vary too much over time.

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Life In Other Planetary Systems

• Extra-solar planets have been found around many
  stars. Therefore, planetary systems are common.
• Planets suitable for life need stable orbits
  (around single stars?)
• Roughly ½ - 2/3 of all stars form in binary
  pairs.
• Life needs time to evolve into intelligent
  species. On Earth, it took us 4.6 billion years.
• Massive stars (hotter than F5) dont live long
  enough.

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Life In Other Planetary Systems

• Life (or Habitable) zone a region around a star
  within which a planet can have temperatures that
  permit the existence of liquid water.
• F stars still evolve too quickly for life to
  evolve and survive long.
• M stars planets would have to be rather close
  to the star, resulting in tidal coupling. M
  stars also exhibit sudden flares.
• Best chance G and K stars.

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Life In Other Planetary Systems

• Galactic habitable zone a region in a galaxy
  within which a planet can develop life.
• Too close to the center stellar density too
  high. Radiation from massive stars and
  supernovae events likely to prohibit the
  development of life.
• Too far from the center not as much material
  from which to create stars. Therefore, not as
  many heavy elements (which go on to be the basic
  building blocks of life) created over time.

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Travel Among the Stars

• If there is life, what is the chance we can visit
  it?
• The nearest star is 4.3 light years away.
• Traveling at the speed of light, it would take
  4.3 years to reach the star (and nothing can
  travel faster than the speed of light).
• Traveling at the speed of light would require
  TREMENDOUS amounts of energy.
• The only way to travel to other locations would
  be to use colony ships where a society of
  people would be born, live and die during the
  trip.
• Would you really travel all that time if you
  didnt know that where you were going were
  habitable?
• Would you really travel all that time and then
  not make your presence known?

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Communicating with Other Civilizations

• If we cant personally travel to other lifeforms,
  can we at least talk with them?
• Radio waves travel at the speed of light.
• While two-way conversations would be difficult,
  we could broadcast information to others.
• For over 50 years, we have been sending out
  signals, in the form of TV and radio broadcasts.
• In 1974, astronomers transmitted a signal towards
  globular cluster M13 (26,000 ly from Earth).

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The Search For Extra-Terrestrial Intelligence

• If we have advanced enough to do this, have other
  civilizations?
• Where would we search for a signal (at what
  wavelength)?
• Above 30 cm noise from the galaxy too strong.
• Below 1 cm Earths atmosphere absorbs incoming
  radiation.
• Still, need to narrow down the range of
  wavelengths.
• The water hole between 21 cm (neutral hydrogen
  emission) and 18 cm (OH emission).

• SETI privately funded by Project Phoenix
• Receives about 2 billion radio bands of data for
  each star.
• seti_at_home - public participants can automatically
  download data to be analyzed by home computers.
  (http//setiathome.ssl.berkeley.edu/)

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• Even with project SETI, we are still only able to
  detect possible signals from a small section of
  our galaxy.

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The Drake Equation

• So how many civilizations with the capability to
  communicate long distances exist?
• The Drake Equation can be used to estimate the
  number of intelligent, communicating civilization
  in our galaxy at this moment.
• N R fp ne fl fi fc L
• R - Rate of star formation in our galaxy for
  stars like our Sun.
• Best estimate 1 star per year.
• fp fraction of Sun-like stars in our galaxy
  with planets.
• Do binary or higher systems of stars contain
  planets (habitable or not)?
• ne average number of planets suitable for life
  per planetary system.
• Depends on the life zone of the star and how many
  stars it orbits.
• fl fraction of suitable planets on which life
  develops.
• fi fraction of planets with life on which an
  intelligent species has evolved.
• fc fraction of planets with intelligent species
  that have developed radio telescopes capable of
  communication.
• L average lifetime of a communicating
  civilization.
• N number of civilizations in our galaxy capable
  of communicating over interstellar distances.