Download Interstellar Communication Exolinguistics SETI Programs

AST 251
Life on Other Worlds
Lecture 11
Interstellar Communication
Exolinguistics
SETI Programs
Duy Cuong Nguyen, P.Eng.
Department of Astronomy and Astrophysics
University of Toronto
News Flash
http://www.spitzer.caltech.edu/Media/releases/ssc2005-09/release.shtml
News Flash
http://www.cnn.com/2005/TECH/space/03/23/craigslist.space/
Let’s move on to something more
cheerful.
Interstellar Communication
Introduction
Intelligent Life
Life that is capable of building radio telescopes
The Sky from the Ground
All
atmosphere
03
H2O,
CO2,
O2
Ionosphere
For astronomers, the interference is communications.
For interstellar messages, the interference is astronomy.
Galactic
synchrotron
background
21
cm
Big Bang
Atmospheric
absorption
Water Hole
λ
300 cm
30 cm
3 cm
Galactic
Galactic
Background
Background
(synchrotron emission)
(synchrotron emission)
The “Water Hole”
The “Water Hole”
3m
300 µm
“Where shall we meet our neighbours?
At the water hole, where species have always gathered.”
λ 300 cm 30 cm
3 cm
3m
300 µm
Water Hole
Galactic
Galactic
Background
Background
(synchrotron emission)
(synchrotron emission)
The “Water Hole”
The “Water Hole”
– Bernard Oliver
1971 NASA design
study for SETI
Telescope – Basic Issues
Wavelength λ
Frequency ν = c/λ
Diameter
D
θ
Minimum Beam Size: roughly θ = λ/D
(Maximum Resolution)
… attained only if mirror surface has bumps no
bigger than about λ/20
Telescope – Basic Issues
Receiver noise
or background
emission
Total amount of light received
increases with area πD2
Wavelength λ
Frequency ν = c/λ
Diameter
D
θ = λ/D
Arecibo: D = 300 m
at λ = 21cm, θ = 2 arcmin
(1/8th the size of the Moon)
D=300m
Beam on sky
Image
A Needle in the Cosmic Haystack
1. Location on sky
1010 stars, or 107 (2’) Arecibo beams
2. Depth into sky
Signal strength – more sensitive receivers (bigger D) can see further.
3. Frequency of radiation (ν, or λ = c/ν)
Consider the AM radio band: there are 210 channels (5 kHz wide)
from 550 kHz to 1.6 MHz; at 1 sec/channel,
scan across dial takes 4 minutes.
In the SETI search, the dial stretches from 1 GHz to 10 GHz
Scan across dial takes 104 years!
(at one point on sky)
4. Polarization
Perfect circular polarization might indicate
intelligent origin – difficult to create in Nature.
5. Time – are we watching at the right time?
A Needle in the Cosmic Haystack
1. Location on sky
1010 stars, or 107 (2’) Arecibo beams
2. Depth into sky
Signal strength – more sensitive receivers (bigger D) can see further.
3. Frequency of radiation (ν, or λ = c/ν)
Consider the AM radio band: there are 210 channels (5 kHz wide)
from 550 kHz to 1.6 MHz; at 1 sec/channel,
scan across dial takes 4 minutes.
In the SETI search, the dial stretches from 1 GHz to 10 GHz
Scan across dial takes 104 years!
(at one point on sky)
Big Problem!
4. Polarization
Perfect circular polarization might indicate
intelligent origin – difficult to create in Nature.
5. Time – are we watching at the right time?
Search early, search often.
Strategies for dealing with frequency uncertainties
1. Search “Magic Frequencies” that any intelligent species should know
Molecule
ν (GHz)
λ (cm)
H
1.4
21
OH
1.7
18
H2CO
4.8
6.2
µ+e- (muonium)
4.7
6
3He+
8.7
3.5
CH3CH2OH
(ethanol)
103
0.29
CO
115
0.26
e+e(positronium)
203
0.15
Perhaps the most important
transition in radio astronomy:
spin-flip transition of electron
within an H atom.
These transitions are absent or
extremely rare in Nature.
One should also consider, say,
these frequencies times
or divided by π or e, say…
2. Build detectors that can scan many frequencies at once
BETA search (Harvard/Planetary Inst.): 8 million channel receiver
Cuts search time down to 11 hours per beam, from 104 years.
Strategies for dealing with frequency uncertainties
Molecule
ν (GHz)
λ (cm)
H
1.4
21
OH
1.7
18
H2CO
4.8
6.2
µ+e- (muonium)
4.7
6
3He+
8.7
3.5
CH3CH2OH
(ethanol)
103
0.29
CO
115
0.26
e+e(positronium)
203
0.15
Perhaps the most important
transition in radio astronomy:
spin-flip transition of electron
within an H atom.
What about Lucy?
Humans have been broadcasting radio and
television for about 50 years.
Traveling at the speed of light, these signals have
gone out 50 light years = 15 parsecs, passing
about 500 stars along the way.
A few of these, like ε Eridani and τ Ceti, are similar to the Sun.
In fact, ε Eridani (a K star 10 light years away) has a planet much like Jupiter
in a 3-AU orbit! It was one of the targets
in the first SETI search by Frank Drake.
Stars less than 25 light years (7.5 pc) away have had time
to reply.
Eavesdropping
W.T. Sullivan, S. Brown, & C. Weatherill, Science January 1978
( undergraduates! )
What could be determined from a nearby star about civilization on Earth?
Civilizations on nearby
stars will see a rapid
rise in the amount
of radio emission and
will probably pay
attention…
Eavesdropping
W.T. Sullivan, S, Brown, & C. Weatherill, Science January 1978
What’s the best indicator of Earthly civilization?
Strongest signals: Military radar.
Problem: not constant; frequency switched to evade jamming.
(& not good ambassadors of goodwill.)
FM Radio: Signal comes out in too broad a band
AM Radio: Doesn’t get out of the ionosphere
Best signal: Television carrier signal
On (almost) constantly.
Very narrow bandwidth.
Eavesdropping
How far away can it be detected?
Arecibo-type detector: TV carrier detectable at 25 light years.
What can you tell?
Use the horizontal beam pattern of a television broadcast tower…
signals get stronger as they cross the horizon as seen from afar.
Eavesdropping
From the pattern of red and blue shifts,
you can tell
In 1 day:
the rate at which Earth rotates about its axis
... and more…
In 1 year:
the rate at which it orbits the Sun
the orbital parameters of the Earth
that the Earth is in the Habitable Zone of the
Sun
Eavesdropping
In the pattern of Doppler shifts and the times of rising and
setting of each transmitter, you can make a map of the planet
If you pay attention to the timing and type of broadcasts, you can
tell something about the number of broadcasting cultures…
Eavesdropping
In addition,
You can tell the size of the radio towers from the width of their broadcast cones.
You can tell something about the weather on Earth from the wobbling of the towers.
You can tell something about…
the power available to human civilization
the sophistication of our broadcast technology
And finally, if you want, you can try to decode the signals themselves…
How far do we have to look?
Simple model for galaxy:
1011 stars
Radius: 1
5 kpc
Width: 500 pc
Volume of galaxy:
π(15 kpc)2x(500 pc) = 3x1011 pc3
You are here.
Volume per star: 3x1011 pc3 / 1011 stars = 3 pc3/ star
… implying a typical spacing of about 1.4 pc between stars.
How far do we have to look?
Important issue: Disk geometry of galaxy creates some diminishing returns.
1. Search radius less than width of
Milky Way (500 pc/2 = 250 pc)
(N* < 20 million)
N* increases as Rsearch3
2. Search must include more
than 20 million stars. Now
N* increases as Rsearch2, because
the flattening of the Galaxy disk is
apparent.
Do we have a chance?
Recall the Drake Equation as of 1961:
the number of civilizations equals the lifetime of a civilization (in years).
N ~ L / yr
If that were true,
How big would L have to be such that a “typical” civilization has time to find
another one?
ch
ar
se
<
20
m
on
ill i
*s
Time enough for
detection
Time enough for
2-way communication
se
ar
About
2000
years
ch
>
20
m
illi
o
n*
s
Do we have a chance?
If we can survive for more than 2 kyr, we have a chance.
If we have a chance, then our current technology must look infantile
to the typical civilization. (Our age is <1/40th of the typical age.)
So it’s a safe bet that we are either alone or in the presence of
civilizations far more advanced than ourselves.
This affects the search strategy somewhat…
1. We must stay alive longer than 2 kyr.
2. We have fewer than 1010/2000 = 5 million stars to search. At some
point we’ll have to start searching at least 2500 per year.
3. We can hope that these advanced aliens are broadcasting for us…
“The probability of success is difficult to assess,
but if we never search the probability is zero.”
– Morrison & Cocconi
SETI’s history so far
N. Tesla, G. Marconi – both thought they heard ET signals.
1924: D.P. Todd – arranged radio silence with U.S. Military during Mars’ closest
approach
1959: P. Morrison & G. Cocconi – Propose a search of the radio sky for
extraterrestrials.
1971: NASA commissions a design study for the ultimate SETI receiver: Project
Cyclops
Arecibo: 0.3 km2
Square Kilometer Array: 1 km2
Cyclops idea: 3 km2
1979-1993: SETI search conducted in Soviet Union and in North America
1980, 1981: Pessimism (arguments by Hart & Tipler). Soviet search terminated.
1993: Congress cuts all NASA funding to the “Great Martian Chase” [Sen. R.Bryan]
Jill Tarter starts the SETI Foundation and Institute.
“Project Phoenix” begins; Berkeley’s SERENDIP project and others continue…
Project Phoenix
• Privately funded
• Does not scan the entire sky
• Listens to sun-like systems most likely to
host long-lived planets capable of
supporting life
• Searches 1 GHz to 3 GHz signals with a
resolution of 1 Hz
Optical SETI
• Proposed in 1961
• Current laser
technology allows for
beams with 5,000x
brightness of the Sun
• Less confusion with
noise
• Better beam focus
• Higher bandwidth
SETI@Home
•
•
•
•
http://setiathome.ssl.berkeley.edu
Distributed computing
Piggy-backs off of observations made at the Arecibo Observatory
Searches 21-cm line (1 418.75 MHz to 1 421.25 MHz)
SETI@Home
SETI@Home
Amateur SETI
Hydrogen Emission Lines along the Galactic Plane
Intelligent Communication
Exolinguistics
How do you communicate with an alien?
Note: Babies solve this problem all the time.
Usual strategy (in a few broadcasts from Earth to star clusters):
1. Modulate the beam to send out a stream of bits
(radio dashes and dots).
2. Repeat the stream so that it’s obvious how many bits are in the
message.
3. Make the # of bits equal the product of two (or three?) prime numbers.
4. Prepare a message that can be viewed as a message if the bits are
arranged as “pixels” in an image…
5. Try to ensure that there is only one way that the pixels of the image can
be interpreted, given the facts of life in the Universe.
- Signal wavelength, frequency: standard of length and time
- Other common points of knowledge: chemistry, astronomy, physics
6. Pack as much information into it as you can without making it illegible.
Exolinguistics
This message was is similar to one sent in
1969 by Frank Drake from the Green Bank
Telescope to the star cluster M13, 25,000
light years away.
But this message is a fake signal Drake
devised to test how well we could decode
one like his.
It is 551 = 19x23 bits long.
It has five sections that each carry
information. What do you think they mean?
Exolinguistics
1. The exoplanets
Host star
four
small
(terrestrial?)
planets
Intermediate planet?
Asteroid belt?
Big planet – like
Jupiter?
Another?
Like Neptune?
Like Pluto?
Exolinguistics
2. Important Elements
for their biochemistry
C: 4 valence
electrons
O: 6 valence
electrons
Exolinguistics
3. Numbers
Exolinguistics
4. Population of planets?
Apparently they’ve started to
colonize their system… they’re
just slightly ahead of us.
(Miraculously.)
Exolinguistics
5. Size and shape of the aliens.
Proactive SETI…
Radio Transmissions
Frank Drake’s Message
Globular Cluster M13
Automated Spacecraft
Pioneer 10 & 11 Plaque
Voyager 1 & 2
Voyager Golden Record
Voyager Golden Record
•
•
•
•
Greetings in 55 languages
UN Greetings
Whale Greetings
Sounds of Earth
•Music of the Spheres
•Volcanoes, Earthquakes, Thunder
•Mud Pots
•Wind, Rain, Surf
•Cricket (Teleogryllus Oceanicus) / Crickets, Frogs
•Birds, Hyena, Elephant
•Chimpanzee
•Wild Dog
•Footsteps, Heartbeats, Laughter
•Fire, Speech
•The First Tools
•Tame Dog
•Herding Sheep, Blacksmith Shop, Sawing, Tractor and
Riveter
•Morse Code
•Ships, Horse and Cart, Train, Truck, Tractor, Bus,
Automobile, F-111 Flyby, Saturn 5 Lift-off
•Kiss
•Mother and Child
•Life Signs
•Pulsar
Voyager Golden Record
• Sounds of Earth
•J.S.Bach Brandenburg Concerto No. 2 in F, First
Movement
•(Java) Kinds of Flowers
•(Senegal) Tchenhoukoumen
•(Zaire) Pygmy Girls’ Initiation Song
•(Australia) Morning Star and Devil Bird
•(Mexico) El Cascabel
•Johnny B. Goode
•(Papau New Guinea) Men’s House Song
•(Japan) Cranes in Their Nest
•J.S.Bach Gavotte en Rondeaux from the Partita
No. 3 in E Major for Violin
•W.A.Mozart The Magic Flute, Queen of the Night
aria, No. 14
•(Georgia) Tchakrulo
•(Peru) Panpipes and Drum Song
•Melancholy Blues
•(Azerbaijian) Ugam
•Stravinsky Rite of Spring, Sacrificial Dance
•J.S.Bach The Well-Tempered Clavier, Book 2,
Prelude and Fugue in C, No. 1
•Beethoven Symphony No. 5 in C Minor, First
Movement
•(Bulgaria) Izlel je Delyo Hagdutin
•(United States) Najavo Night Chant
•Holborne Fairie Round, from Paueans, Galliards,
Almains and Other Short Aeirs
•(Solomon Islands) Melanesian Panpipes
•(Peru) Wedding Song
•(China) Flowing Streams
•(India) Jaat Kahan Ho
• Dark Was the Night
•Beethoven String Quartet No. 13 in B flat, Opus
130, Cavatina
About Us
Basic Math
Basic Units
Basic Astronomy
Basic Chemistry
Basic Biology
Vertebrate Evolution
Human Biology
Human Development
Human Education
Human Society
Human Society
Human Science
Human Science
Human Art
Human Progress
Human Progress
Caution
Caution
In Conclusion
AST 251
Life on Other Worlds
Next Time:
Interstellar Travel
Galactic Colonization
End of AST 251
Lecture 11