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The search for extraterrestrial
Dominated by quests for radio
beacons, but with some searches
for narrow-band laser
Fig. 20-11, p.423
Fig. 20-17, p.428
Why SETI will Fail
High-resolution imaging of
young planets
New infrared results from the VLT
and the HST
Essentials of planet imaging
• Young, preferably nearby, target stars
• A high spatial resolution infrared camera
system on a large ground-based
telescope or on the Hubble Space
Adaptive Optics Imaging
• At current state of the art, AO is sufficiently sensitive
to detect only thermal emission from self-luminous,
young planets. Reflected light is too feeble to be
• AO detectability is a function of a planet’s age,
distance from Earth, and contrast with its primary
Planet imaging programs
• Keck AO
To date, each telescope has been used to
image ~100 stars
Fig. 20-3a, p.418
Where do humans stand on
the scale of cosmic
• Carl Sagan’s natural evolution of the
Universe: Origin of the Universe =>
origin of galaxies, stars, elements,
planets => origin of life => chemical and
biological evolution => technological
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 we’re 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…”
Discoveries of extrasolar
• Exoplanets => ETI is *less* likely for two
Minor reason: planetary systems are
unfavorable for life as we know it (but only for
Primary reason: people’s great interest in these
We live in a unique moment in history:
SETI, but no “terrestrial planet finder”
AIRS spectrum
TPF/Darwin design concepts
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
Suppose that TPF discovers a
“living world”
What happens next? SETI:
For a decade? A century? A
If there is no answer, then our
descendants can choose between
two options:
1) do nothing (for a million years)
2) send a spaceship
• 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.
Biologist Penelope Boston,
from the Discovery Channel’s
program “Destination Mars”:
“I am a biologist; I have a burning
need to know about life in the
But dinosaurs, bugs, and
flowers don’t do radio
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.
Robotic Interstellar Exploration in
the 21st Century
• 1998 NASA/JPL 2-day workshop
• Engineers & Scientists
• What “hook” might motivate humankind
to provide the $$ needed to fund a
mission to a nearby star?
Now let’s turn the situation
around and look at things
from the perspective of a
technological extraterrestrial.
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.
In summary, three simple
postulates have major
implications for SETI.
1) Soon after development of technology, all
civilizations will build the equivalent of TPF.
2) 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.
Extrasolar planets
=> ETI is now *less* likely
than previously because of
people’s great interest in
such discoveries.
(because of life)
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.
What is a planet?
• The IAU Definition:
• Mass < 13.6 Jupiter masses
• Orbits a star or stellar remnant
• Don’t use formation mechanism to
decide if yes or no
Light from
science target
Perfect Plane Wave
Atmosphere corrugates
the wavefront
Creates blurred
Seeing disk ~ 1
Light from
science target
Light from
reference star
Creates partially
sharpened images
FWHM ~ 0.040
Beam Splitter
Cooling Curves for Substellar Objects
Evolution of M Dwarf Stars, Brown Dwarfs
and Giant Planets (from Adam Burrows)
STARS (Hydrogen burning)
-2 2M1207A
80M jup
200M jup
NICMOS Companion Detection Limit (M type primary)
14M jup
Log 10 Age (years)
Epoch 5 astrometry - NICMOS
Unequivocal common P.M.
Solar system time scales and
ages of young nearby stars
• Formation of Jupiter
• Formation of Earth’s core
• Era of heavy bombardment
in inner solar system
 Cha cluster
TW Hydrae Assoc.
 Pictoris moving group
Tucana/Horologium Assoc.
AB Dor moving group
< 10 Myr
~ 30 Myr
~ 600 Myr
8 Myr
8 Myr
12 Myr
30 Myr
70 Myr
2M1207A/b - 26 APR 05
NICMOS F160W (1.6mm)
-2 to +2 ADU/second/pixel