Transcript Life in the Universe

SETI
Search for Extra Terrestrial Intelligence
FYOS
Lecture 8
History
• Guglielmo Marconi (1874-1937)
o 1st cross-Atlantic radio
communication
• Nikola Tesla (1856-1943)
o inventor of AC current
They both claimed to hear a radio
signal from alien worlds. In fact,
they both heard atmospheric
“whistlers”
In 1924, when the Mars was close
to Earth, a large campaign to
hear a signal from Mars…
 Destined to fail. Why?
• Ionosphere acts as a mirror for radio waves…
Whistler
• Hearing distant lightnings!
Modern Approach
• Cocconi and Morrision at Cornell calculated in 1959 that it is possible to
send radio signals b/w stars even with the technology of 50s…
• Galaxy is quite old  must be more advanced civilizations than us in the
Galaxy  they may send “hailing signals” to other stars very easily!
? which radio frequency ?
Choice of Frequency
• Neutral Hydrogen gas produces a 1420 MHz (21cm) wave  natural static
radio noise…
• Uniqueness of this frequency : Hydrogen is the most common element in
the Universe, hence any astronomers in advanced civilizations would use
this frequency to study Galaxy!
Modern SETI
• Cocconi and Morrison persuaded fellow radio
astronomers but no positive response.
• In 1960, Frank Drake independently arrived
at a similar conclusion and performed a
week-long search for alien signals at two
stars (ε Eri and τ Ceti)  caught the
attention of the astronomy community.
• NASA started a dedicated program which
finally started its operation in 1992. In 1993,
the program got canceled by the U.S.
Congress.
Categories of Signals
• In Frank Drake’s 1960 experiment: searched for an “intentional” signal sent
to us: an interstellar hailing signal.
Three possible types of alien signals
1.
intentional signal beacons.
2.
aliens’ local communication.
e.g., our own radio and TV signals
3.
alien world’s inter-planetary or interstellar communication.
our communication signals with interplanetary spacecrafts (e.g., Voyager)
Can aliens detect our leaked signals?
• Our signal has no intended direction
 to reach out to many homes…
• Because of the inverse square law, the
signal gets weaker very quickly…
• With the technology similar to ours, our
leaked signal can be detected only about
one light-year away from Earth!
• The nearest star is 4 light-years away…
This means that we can’t detect alien’s local
communication signals (unless they use
much stronger signal)
We can detect only an intended signal from
aliens at this point.
Format of Signal
• Intended messages should be easy to decipher…
 what communication protocol?
• In the movie , “Contact”, Carl Sagan suggested that aliens may use our
leaked TV broadcast as a clue embedded in their message… But, our signal
reaches only 50 light-years…
We sent out a radio signal
using the world’s largest
antenna (Arecibo) in 1974
toward M13!
Arecibo 1974 signal
1,679 bits in a 3-minute message
 1,679 = a multiple of two prime numbers (23, 73).
alien needs to know that the message was a 23x73
image…
single transmission
Even if we detect an alien signal,
we may never decode it!
How to decipher?!?
• Arecibo message deciphered as 73x23 image…
Difficulties with
Radio SETI
• Two challenges
1.
No dedicated search telescope  all SETI
programs so far had to compete for
telescope times against other traditional
astronomy research projects…
2.
terrestrial interferences
o
o
o
o

TV broadcasts
Radio stations
Radars
etc.
exactly the types SETI look for!
Build a telescope on the far-side of the Moon!?
Current Radio SETI
• SETI institute  350 6-m
radio telescopes near
Berkeley…
• 450 million channels
• 70 megawatts from 100
lightyears away.
Current Radio SETI
• UC Berkeley
• SERENDIP – “piggyback”
• 168 million channels
1 megawatt
SETI@Home (2-3% of data)
Current Radio SETI
• Southern SERENDIP
• Parkes 64m telescope in Australia
• 58 million channels, 1 megawatt
Current Radio SETI
•
•
•
•
SETI Italia
32m Medicina telescope
24 million channels
30 megawatts
So, any detected signal so far?
Anything interesting?
Active SETI
• sending a message to aliens = Messaging to Extra Terrestrial Intelligence
(METI)
• Is it safe to send a message to aliens??
1974
Arecibo message
1999
Cosmic Call 1
2001
Teen Age Message
2003
Cosmic Call 2
2008
A Message from Earth
Optical SETI history
• C. Townes invented a LASER in 50s
• In 1961, Schwartz and Townes published a science article “Interstellar and
Interplanetary Communication by Optical Masers” in Nature.
• Then, Project Cyclops in 70s shadowed the Optical SETI…
(diameter = 16km)
Beamed versus Omni-directional
versus
At 100 Ly away with an Arecibo-like receiver: omni-directional signal requires to be
66,000 MW, while a beam signal to be only 0.0033MW.
Optical SETI
• High intensity pulsed laser
beam from an alien who
knows that we are here!
• Highly beamed laser beam
can outshine the host star by
1000+ times!!
• No human interference!!
With 10m telescopes on both ends…
• Can send a high quality signal (large amount of info) out to ~1,000 lightyears with our 21C Earth laser technology already!
On-going Optical SETI
• UC Berkeley: Lick observatory (1.2m telescope)
On-going Optical SETI
• Harvard Univ. funded by
Planetary Society
• Some collaboration with
Princeton Univ.
• 3 OSETI projects
• 1.5m telescope
On-going Optical Search
• Columbus (Ohio) Optical SETI by Stuart Kingsley (Amateur Astronomer)
• Using off-the-shelf instruments… (10inch reflector Meade)
Advantages of OSETI over Radio SETI
1.
2.
3.
4.
5.
Visible light-emitting devices are smaller and lighter than microwave or
radio-emitting devices.
Visible light-emitting devices produce higher bandwidths and can
consequently send information much faster.
less Interference than radio
Naturally occurring nanosecond pulses of light are nonexistent.
unlike in microwave and radio SETI, searching for an exact frequency is
not vital because the expected transmitting beam should outshine the
unfiltered light from the star by at least 30 times.
Next Week : SETI debate…
• Read two articles before you come to the class…