SETISearch for Extra Terrestrial Intelligence

ASTR 1420

Lecture 20

Sections 12.3

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 some 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 signals1. 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 signalusing the world’s largestantenna (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

M13 : 21000 light-years away, a globular cluster with ~1 million stars!

Why M13?

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 interferenceso TV broadcastso Radio stationso Radarso etc. exactly the types SETI look for!

Build a telescope on the hidden 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

Still on-going…

How long do we need to wait?

Is there a better way?

Active SETI

1974 Arecibo message

1999 Cosmic Call 1

2001 Teen Age Message

2003 Cosmic Call 2

2008 A Message from Earth

• sending a message to aliens = Messaging to Extra Terrestrial Intelligence (METI)

• Is it safe to send a message to aliens??

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 light-years 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. Visible light-emitting devices are smaller and lighter than microwave or radio-emitting devices.

2. Visible light-emitting devices produce higher bandwidths and can consequently send information much faster.

3. less Interference than radio4. Naturally occurring nanosecond pulses of light are nonexistent.5. 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.

Other Attempts (or suggestions)

• Artifacts which can be detectable from a great distance…

• Karl Gauss (1777-1855) suggested planting trees in Siberia in the form of a right triangle so that it can be recognized by peoples on the Moon…

• Dig trenches in the Sahara in various geometric shapes and fill them with oil and lit.

Alien Artifacts

Instead of sending a signal, advanced aliens might have visited US already and buried their instruction somewhere in the Solar System!

• Some believe that UFOs, crop circles, etc. are those… • 2001: A Space Odyssey : Advanced alien being buried their signaling device

under the ground of the Moon.

Best to places to hide

• Lagrange Points

Level of Technological Advancement

• Nikolai Kardashev (1932 -- ) : based on the amount of usable energy at alien’s disposal.1. Type I – planetary civilizations : use the resources of their home plane (us!)

energy usage upto 1017 Watts

2. Type II – stellar civilizatons : a civilization that is able to harness all of the power available from a single starenergy usage up to 1026 Watts

3. Type III – Galactic civilizations : can employ the resouseces of the entire galaxy

energy usage of 1037 Watts

Detecting Type II civilizations

• If we capture the energy released by the Sun for just 1 second…

enough energy for us to live next 1 million years!

• Advanced civilization, in a full scale usage of their host star energy, could have built a thin-wall energy collecting sphere around their star

Dyson sphere

Dyson Sphere in the Startrek

Seen from the USS Enterprise bridge

Dyson Sphere in the Startrek

The Enterprise in orbit around the Dyson sphere

Variants of Dyson Sphere

Dyson Ring Dyson Swarm

How thoroughly have we searched for?

In summary…

Important Concepts• Choice of Frequency• Three possible alien radio signals• But, with our current technology,

we can only detect an “intended” broadcast signal.

• Advantages of OSETI• Kardashev’s categories of

civilizations

Important Terms• SETI• METI• Optical SETI• Dyson Sphere

Chapter/sections covered in this lecture : 12.3Longevity of Civilization + Will SETI fail?: next class!!