Active SETI Strategy:Communicating with Extraterrestrial Life
William AntoneLuis Cartagena
Jorene Ooi
Outline● Active vs. Passive Seti● Technology● Targets● Past & Present Messages● Message Content
Active SETI
Credit: pbs.org
Active SETI
Radio Messaging● radio telescopes● detectable across galaxy
repetitionnanosecond pulsesdetectable across galaxy
xLaser Messaging
New Strategy for Transmission
● combining powerful lasers with large optical telescopes
● pulse sensor + keck telescope → can outshine the star at 1000 light years
● Sun-like stars or solar-system-like Exoplanets System● nearby stars● known planets● should not be limited
Where to point?
Physical Messages
Credit: NASA
The Morse Message (1962)● From Evpatoria
Planetary Radar● Directed to Venus● “MIR, LENIN, SSSR”
Credit: NASA
Arecibo Message (1974)
Credit: Cornell University
Evpatoria Planetary Radar
● Cosmic Call 1 (1999)○ four transmissions○ arrival: 2051-2069
● Cosmic Call 2 (2003)○ five transmissions○ arrival: 2036-2049
Credit: S. Korotkiy
Teen Age Message (2001)● Section 1:
monochromatic radio wave
● Section 2: 15-min “1st Theremin Concert for Aliens”
● Section 3: greeting texts, image glossary
Credit: Alexander Zaitsev
A Message from Earth (2008)● Gliese 581 c● 20 light years away● Arrival date: Feb
2029● crowdsourced
messages translated into binary
Credit: Lynette Cook / NASA
“Wow!” Signal
● “Wow!” signal detected Aug. 15, 1977● Ohio State University Radio Observatory (OSURO)
Credit: Jerry Ehman, Paul Schuch
Wow! Reply (2012)● Sent by National Geographic & Arecibo Observatory● Twitter messages and videos from celebrities
"We are not delicious. In fact, we're kind of gamey, and we get stuck in your teeth. It's really embarrassing at a job interview. If you want something good to munch on, go to the nearby Crab nebula. And bring a bib. Seriously, all you can eat."
Credit: Frank Micelotta / Getty Images
Electromagnetic Leak
“If extraterrestrial civilizations are monitoring our TV broadcasts, then this is what they are currently watching.”
Credit: Abstruse Goose
We’re already doing enough?● Would radio and TV signals generate an
“automatic reply”?● Current TV signals too low in gain● Likely only a transitory activity
Message Length LimitationsSignal to Noise RatioWide Bandwidth: Harder to detect
Efficient communicationNarrow Bandwidth: Easier to detect
Inefficient communication
Message Length LimitationsRepetition will be necessary
Assume one-way message
Creating Artificial LanguageHuman Language
Culturally dependentImpreciseOverly Complex
Constructing the MessagePreamble (Facts we presume them to know)
NumbersScienceGroup Theory and Sets
“Encyclopedia Galactica” (All about us)
Numbers
Source: Evpatoria Message
Group Theory and SetsHuman: = Man or Woman 7 billion humans included in EarthM + 80 years => {} W + 80 years => {}
Interstellar Rosetta Stone
Elementary encyclopedia of terrestrial knowledge
Used in Cosmic Call 1 and Cosmic Call 2
263,906 bits, 127 symbols, 2078 lines over one “page”
Credit: Seed Magazine
Interstellar Rosetta Stone
Size and ordering of solar system
Mass and radius of Jupiter and the Sun
Credit: Seed Magazine
Interstellar Rosetta Stone
Biosphere
Chemical composition of Earth atmosphere, continents, oceans
Altitudes
Credit: Seed Magazine
Interstellar Rosetta Stone
Average height
Denotes “up” and “down”
Credit: Seed Magazine
Interstellar Rosetta Stone
Human population, average mass, average temperature
Perceptual limitations (light and sound)
Credit: Seed Magazine
Interstellar Rosetta Stone
Molecular structure of adenine, thymine, guanine, and cytosine
Credit: Seed Magazine
Interstellar Rosetta Stone
Typical cell , size and quantity
DNA structure and location in the nucleus
Credit: Seed Magazine
Conclusion● Many different technologies to communicate● Large amounts of space to target● Constructing a message is difficult