SETI

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SETI

• The search for extraterrestrial intelligence
• Dominated by quests for radio beacons, but with
  some searches for narrow-band laser transmissions

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Fig. 20-3a, p.418
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Where do humans stand on the scale of cosmic
intelligence?

• Carl Sagans natural evolution of the Universe
  Origin of the Universe gt origin of galaxies,
  stars, elements, planets gt origin of life gt
  chemical and biological evolution gt
  technological intelligence

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National Enquirer Headline (3/89) Americas
most powerful radio telescope IS ZAPPED! by
hostile space aliens!

• We know that extraterrestrials have shot down
  planes and abducted people, but this is the first
  time they have been brazen enough to destroy a
  government research facility!

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From the SETI Institute webpage (10/15/05), on
The future of SETI research

• Scientists who participate in this research are
  more optimistic than ever before that they could
  find signals from space that would indicate that
  were not alone. They are bolstered in this view
  by several recent developments. In the past 5
  years astronomers have found that many stars have
  planets

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Some challenges for SETI
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Atmospheric pressure and composition of Solar
System planets
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But these are gas giant planets

• To find life as we know it, we must image
  terrestrial planets in the zone of life. For
  SETI, this means a planet sufficiently close to
  its star that water will be warmed to the liquid
  state (an ice covered planet will not do, nor
  will a planet completely covered with liquid
  H2O).

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Two potential milestone space missions beginning
in 2009

• Kepler (transiting super-Earths?)
• JPL role
• March 6 launch
• Herschel (cool dust)
• Largest diameter space mirror
• JPL role
• May 6 launch

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• We live in a unique moment in history
• SETI, but no terrestrial planet finder
• (TPF)

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AIRS spectrum
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Wavelengths of Interest
The interesting region
Methane in Earths oxygen is out of chemical
equilibrium by 140 orders of magnitude
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The Characterization ProblemDetermine
atmospheric and surfaceproperties with special
attentionto biosignatures.
Venus
Mars
Earth
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TPF/Darwin design concepts
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• These are first-generation instruments.
• Later generations could image Earth-size worlds
  revealing continent-ocean dichotomies, annual
  seasonal variations, the coming and going of ice
  ages, and long-term changes in vegetation
  patterns, both natural and human induced.

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Suppose that TPF discovers a living world

• What happens next? SETI
• For a decade? A century? A millennium?

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If there is no answer, then our descendants can
choose between two options1) do nothing (for a
million years)2) send a spaceship
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• Everything we know about human nature and history
  indicates that intelligent creatures will follow
  the latter path --
• Exploration of our solar system began with
  telescopic observations from Earth. But as soon
  as we developed the capability, we launched
  spaceships to explore planets and moons up close
  because observing from afar is limited and,
  ultimately, unsatisfying.

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Biologist Penelope Boston, from the Discovery
Channels program Destination Mars

• I am a biologist I have a burning need to know
  about life in the Universe

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But dinosaurs, bugs, and flowers dont do radio
telescopes

• Passively pointing a radio telescope at a living
  world that lacks a technological civilization
  will never get Dr. Boston to where she wants to
  be --
• e.g., knowledge of whether all life is carbon
  based or uses liquid water as a solvent, or is
  constructed from proteins and nucleic acids.

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Robotic Interstellar Exploration in the 21st
Century

• 1998 2-day NASA/JPL workshop
• of engineers scientists
• What hook might motivate humankind to provide
  the needed to fund a mission to a nearby star?

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By effectively unanimous consent that hook was
agreed to be a living world

• and TPF/Darwin will give to mankind the ability
  to identify living worlds

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The problem of interstellar travel is a problem
of motivation and not of physics

• Freeman Dyson
• In Essays in Honor of Hans A. Bethe (July
  1966)

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Why are Kiwis so keen for life on the edge?

• Peter Hillary (son of the late Sir Edmund
  Hillary) who has himself climbed Everest twice
• We want action for ourselves. We dont want to
  sit around listening to other peoples yarns.

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Now lets turn the situation around and look at
things from the perspective of a technological
extraterrestrial in a planetary system within a
few 100 light years of Earth
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Simulated Planet Imager View of the Earth(20??
Launch or maybe 2??? Launch)
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A million years ago, having seen our amazing
planet with their TPF, what is their next move

• Are they doing SETI?
• Are they curious?
• Can they build spaceships?

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Three simple postulates have major implications
for SETI.

• Soon after development of technology, all
  civilizations will build the equivalent of TPF.
• Intelligent life is curious about other life
  forms, simple or technological.
• 3) Having used TPF to discover a nearby living
  world, spaceships will be constructed to visit
  that world.

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If these simple postulates are true, then the
absence of intelligent aliens in our solar system
is strong evidence that they do not exist
anywhere in our region of the Milky Way and SETI
searches of nearby stars are destined to fail.
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To conclude, lets look at far away and long ago

• Earth, thanks to life, has had an oxygenic
  atmosphere for about 2 billion years. Any
  extraterrestrials who possess the equivalent of
  our TPF and who passed near our Sun during those
  years, would have discovered our unusual
  atmosphere.

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During the past 2 billion years, millions of
sun-like stars have passed near our solar system
--Yet no one has come here in all this time.
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Interstellar distances are no barrier to a
species which has millions of years at its
disposal

• Freeman Dyson
• In Disturbing the Universe
• 1979

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The marriage of space telescopes and interstellar
spaceships guarantees that if extraterrestrials
civilizations were common, then someone would
have come here long ago.
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Thus, the only SETI strategy that makes sense is
to search for signals from distant
civilizations

• Signals received from such (uncommon) and distant
  beings are unlikely to have been generated for
  our benefit, so their detection may well require
  luck, and round-trip communications will be very
  slow

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It will be our seed that will populate the Milky
Way Galaxy

• We will be the little green women and men

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Logical consistency demands that SETI TPF go
together like a horse carriage (you cant have
curiosity about one without the other)

• Should a long-lived society lack the curiosity to
  do TPF, then it is logically inconsistent to
  expect that it will be doing SETI.

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You now have a chance to observe on the new 42
antenna Allen Telescope Array!

• The ATA is accepting proposals from the general
  user community for the 2nd half of 2008.
  Proposals are due April 18, 2008 at 5 p.m. PDT

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Terrestrial Planet Finder (TPF) Missions
resolve an ancient and fundamental question.
There are infinite worlds, both like and unlike
this world of ours. -Epicurus (341-270 BC)
There cannot be more worlds than
one. -Aristotle (384-322 BC)
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Fig. 20-11, p.423
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Light from science target
Creates blurred images Seeing disk 1 arcsecond
Perfect Plane Wave
Atmosphere corrugates the wavefront
Telescope System
Science Camera
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Creates partially sharpened images FWHM 0.040
arcsecond
Deformable Mirror
Science Camera
Beam Splitter
Wavefront Sensor
Computer
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Discoveries of extrasolar planets

• Exoplanets gt ETI is less likely for two
  reasons
• Minor reason planetary systems are unfavorable
  for life as we know it (but only for 10)
• Primary reason peoples great interest in these
  discoveries

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Extrasolar planets

• gt ETI is now less likely than previously
  because of peoples great interest in such
  discoveries.
• (because of life)

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Why SETI will Fail