1. Search for Extraterrestrial Intelligence
SETI
Michael L. Sitko
University of Cincinnati
June 29, 2004

2. 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

3. “Attempts” at Communication
c Karl Gauss - plant huge forest of trees in the form of a right triangle Look at Mars for same?
c Joseph von Littrow - light trenches filled with kerosene
N. Tesla attempts to send a powerful burst of radio noise as a "message" and then listen for a reply.
G. Marconi, tries to listen for radio signals from a boat in a remote oceanic location.

4. OZMA - The first modern radio search
David Morrison & Giuseppi Cocconi propose radio search for signals from intelligent extraterrestrials (September 19 issue of Nature)
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

5. How Many Intelligent Civilizations Are There?

6. Rate of Star Formation The Milky Way Galaxy is about 14x109 years old
It contains roughly 200x109 stars
Mean rate of star formation:
But most of this occurred early on - the rate is probably about 1/10 of this, about 2 stars/year.

7. Finding Extrasolar Planets
Direct Imaging
Proper Motion Studies
Doppler Searches
Transit Searches

9. Doppler Searches

10. Epsilon Eridani - an original Ozma target

11. Transit Searches
HD b

12. Ne
Most dynamic models of 1990s suggested ~1 terrestrial planet in CHZ.
Most KNOWN planetary systems dominated by HOT JUPITERS!
Ne may be small!!

13. 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!

14. Darwin (ESO) & TPF (NASA)

15. Ecozone Issues Energy absorbed by planet: Written another way:
Energy emitted by planet:
Equilibrium T for planet:

16. Example: Our Solar System:
Planet dp a Predicted T Observed T
Mercury 5.8x
Venus 1.1x
Earth 1.5x (290 avg.)
Mars 2.3x (SubSolEq)
Jupiter 7.8x (cloud tops)
Saturn 1.4x (cloud tops)
What Goes?

17. 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

18. Hart Models (1980)

19. Continuously Habitable Zones
Michael Hart (1980) Require liquid water for 0.8 Gyrs, etc.
Stellar Mass Spectral Type Inner r of CHZ Outer r of CHZ Thickness
(solar masses) (AU) (AU) (AU)
> Red Giant Too Soon
1.20 F
1.15 F
1.10 F
1.05 G
1.00 G
0.95 G
0.90 G
0.85 K K
In all cases, thickness is less than 0.1 AU

20. Recent Models - Kasting et al.
Newer models handle CH3 and NH3 more realistically.
Suggests

21. 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~ yrs??

22. Put It All Together Obviously very uncertain!
The only way to know for sure is to LOOK!

23. 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)

24. Signal Types - Radio

25. Programs - Past, Present, and Future
Ozma
Frank Drake
OSU

26. Megachannel Extraterrestrial Assay (META)
Paul Horowitz
META Processors
Harvard 26-m radio telescope

28. NASA SETI
Sky Survey
16 million channels GHz - equivalent to 10 billion “Ozmas”
Target Search
14 million channels GHz - looking at 1000 stars
Project cancelled by US Congress after 2 megachannel receiver/processor began.

29. Main BETA rack - containing 63 FFT boards (each processing 4 million channels)

31. 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

32. Allen Telescope Array

33. Optical SETI Proposed in 1961 by R. Schwartz & C
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

34. Message Transmitted from Arecibo - 1974
What Would a Message Look Like?
Binary (or Morse Code) strings of “special” numbers - primes, etc.
Message Transmitted from Arecibo

35. 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.