Download Search for Extraterrestrial Intelligence

Search for Extraterrestrial
Intelligence
SETI
Michael L. Sitko
University of Cincinnati
June 29, 2004
Early Speculations
c. 400 BCE - Metrodorus of Chios - "It is unnatural in a large
field to have only one shaft of wheat and in the infinite
universe only one living world.”
c. 50 BCE - Lucretius - "Nothing in the universe is unique
and alone, and therefor in other regions there must be other
Earths inhabited by different tribes of men and breeds of
beasts.”
Giordano Bruno - there must be "an infinite number of suns
with planets and life around them". Burned at the stake in
1600 CE
“Attempts” at Communication
c. 1820 Karl Gauss - plant huge forest of trees in the form of
a right triangle Look at Mars for same?
c. 1840 Joseph von Littrow - light trenches filled with
kerosene
1899 - N. Tesla attempts to send a powerful burst of radio
noise as a "message" and then listen for a reply.
1922 - G. Marconi, tries to listen for radio signals from a boat
in a remote oceanic location.
OZMA - The first modern radio
search
1959 - David Morrison & Giuseppi Cocconi propose
radio search for signals from intelligent extraterrestrials
(September 19 issue of Nature)
1960 - Frank Drake looks at 2 stars
(Tau Ceti & Epsilon Eridani) at 1
wavelength (H I 21-cm line) with
85-ft NRAO dish for a few months.
SETI established as an experimental
science
How Many Intelligent
Civilizations Are There?
Number of intelligent civilizations
N ic  Ric  Lic
Ric  rate of formation of intelligent civilizations
Lic  lifetime of intelligent civilizations
N ic  R* Pp Pe N e PL PI Lic
R* rate of star formation
Pp probability of having planets
Pe probability that ecozone lasts long enough
N e number of planets in ecozone
PL probability that life will arise
PI probability that intelligence will arise
Rate of Star Formation
The Milky Way Galaxy is about 14x109 years old
It contains roughly 200x109 stars
9
200x10
stars
Mean rate of star formation:
 14stars / year
9
14x10 years
But most of this occurred early on - the rate is probably
about 1/10 of this, about 2 stars/year.
Finding Extrasolar Planets
•Direct Imaging
•Proper Motion Studies
•Doppler Searches
•Transit Searches
Doppler Searches
Epsilon Eridani - an original Ozma target
Transit Searches
HD 209458b
QuickTime™ and a
GIF decompressor
are needed to see this picture.
Ne
Most dynamic
models of
1990s
suggested ~1
terrestrial
planet in CHZ.
Most KNOWN
planetary
systems
dominated by
HOT
JUPITERS!
Ne may be
small!!
Probability of Having Planets
Searches for
extrasolar planets
suggests that this
number is 0.2 or
greater. Current
searches are still
not complete.
This depends on
the metallicity of
the star!
Darwin (ESO) & TPF (NASA)
Ecozone Issues
Energy absorbed by planet:
L
*  cross section  (1 albedo)
4 d 2p
Written another way:
4 R2 T 4
* *  R2 (1 a)
p
4 d 2p
Energy emitted by planet:
4 R2p T p4
Equilibrium T for planet:
T 
p
1
2
(roughly...)
R
* (1 a)1/4 T
*
d
p
Example: Our Solar System:
Planet
Mercury
Venus
Earth
Mars
Jupiter
Saturn
dp
a
Predicted T
5.8x1012
1.1x1013
1.5x1013
2.3x1013
7.8x1013
1.4x1014
0.056
0.76
0.39
0.16
0.51
0.61
440
230
250
220
104
81
What Goes?
Observed T
100-620
750
180-330 (290 avg.)
130-290 (SubSolEq)
160 (cloud tops)
90 (cloud tops)
Simulate Evolution
Rate of outgassing of volatiles (H, C, N, O) from the interior
Condensation of H2O vapor into oceans
Solution of atmospheric gases into oceans
Photodissociation of H2O in the upper atmosphere
Escape of H from the uppermost atmosphere (exosphere)
Chemical reactions in atmospheric gases
Presence of life and variations in biomass
Photosynthesis and burial of organic sediments
Urey reaction (CaSiO3+CO2CaCO3+SiO2)
Oxidation of surface minerals (2FeO+OFe2O3)
Variations in the luminosity of the Sun
Variations in the albedo of the Earth
Greenhouse effect
Hart Models (1980)
Continuously Habitable Zones
Michael Hart (1980) Require liquid
water for 0.8 Gyrs, etc.
Stellar Mass
Spectral Type Inner r of CHZ
(solar masses)
(AU)
>1.20
1.20
1.15
1.10
1.05
1.00
0.95
0.90
0.85
0.835
F7
F8
F9
G0
G2
G5
G8
K0
K1
1.616
1.420
1.240
1.086
0.958
0.837
0.728
0.628
0.598
Outer r of CHZ
(AU)
Red Giant Too Soon
0.054
0.061
0.069
0.064
0.046
0.030
0.015
0.001
0.000
1.668
1.481
1.310
1.150
1.004
0.867
0.743
0.629
0.598
In all cases, thickness is less than 0.1 AU
Thickness
(AU)
Pe
0.01
Recent Models - Kasting et al.
Newer models
handle CH3 and
NH3 more
realistically.
Suggests
Pe  0.01
Life Issues
Probability that Life Evolves - Life appeared on Earth as soon
as it was climatologically possible. Existence of
“extremophiles” suggests PL~1 . But we may be fooling
ourselves - only 1 example.
Probability that Life Develops “Intelligence” - again only 1
example. PI~1??
Lifetime of Intelligent Communicative Life - We have had
the ability to “communicate” for ~50 years. Might have been
as small as 10 years (Cuban Missile Crisis), but we or others
might survive for the lifetime of the Sun. Lic~10-1010 yrs??
Put It All Together
N ic  R* Pp Pe N e PL PI Lic 
    11L
2
yr
1
5
1
10
1
10
 0.044Lic ~ 0.44  BIG
If
N ic  106  separation  100 pc
If
N ic  50  separation  2000 pc
Obviously very uncertain!
The only way to know for sure is to LOOK!
ic
Search Strategies
Directed - use a major facility for short periods of time.
Target Search - look at specific, promising stars
Sky Survey - look everywhere
Shared - use observations from other projects. You can
analyze old data, or make "parasitic" observations.
Dedicated - use a facility exclusively (or at least
primarily) for SETI work (in Target Search or Sky Survey)
Signal Types - Radio
Programs - Past, Present, and Future
1960 - Ozma
Frank Drake
1973-1997 - OSU
Megachannel Extraterrestrial
Assay (META)
Paul Horowitz
META Processors
Harvard 26-m
radio telescope
NASA SETI
Sky Survey
16 million channels - 1-10 GHz - equivalent to 10
billion “Ozmas”
Target Search
14 million channels - 1-3 GHz - looking at 1000 stars
Project cancelled by US Congress after 2 megachannel
receiver/processor began.
BETA
BETA
Main BETA
rack containing
63 FFT
boards (each
processing 4
million
channels)
SETI Institute (founded in 1984)
&
Project Phoenix
Continuation of Target Search
under Private Funding!
Parkes 210-ft, Green Bank 140-ft,
Arecibo 1000-ft telescopes
Allen Telescope Array
Optical SETI
Proposed in 1961 by R. Schwartz & C. Townes
First carried out in 1990 by Stuart Kingsley in Columbus, OH
High-power narrow-band lasers can outshine
the Sun at the emitting wavelengths
Look for short pulses with coincidence
counters
What Would a Message Look Like?
Binary (or Morse Code) strings of “special”
numbers - primes, etc.
Message Transmitted from Arecibo - 1974
What if We Hear “Them”? - SETI Protocol
1. Is it really extraterrestrial?
2. Get confirmation from other astronomers. (If
extraterrestrial, tell your government about it).
3. If convincing: announce to International Astronomical
Union, Secretary General of the UN, inform SETI groups.
4. Make the first public announcement
5. Make data available to all.
6. Everyone carefully record & disseminate signals
7. Protect frequencies.
8. Don't broadcast back to the ETs! Requires Debate.
9. Study signals. The SETI Committee of the International
Academy of Astronautics keeps a list of experts to call on.