• WHY WE EXPLORE
• PLANETARY NEWS
• SPACE TOPICS
  • Contests, Events, and Awards
  • Extrasolar Planets
  • How It Works
  • Near Earth Objects
  • Our Solar System
  • Search for Life
    • Search for Extraterrestrial Intelligence
      • SETI Facts
      • The Planetary Society and SETI
      • SETI Features
  • Space Missions
• FOR KIDS

browse projects: Apophis Mission Design Competition Asteroid Impact Mapping System Catalog of Exoplanets Drive a Mars Rover Extrasolar Planets Transit Search International Lunar Decade LIFE Experiment: Phobos Mars Climate Sounder Team Website Messages from Earth Observing Earth Pioneer Anomaly Planetary Microphones S.O.S: Save Our Science! SETI Optical Telescope SETI Radio Searches SETI@home Shoemaker NEO Grants Solar Sailing Space Advocacy Space Information Stardust@home Target Earth Visions of Mars

browse space topics: 2001 Mars Odyssey Asteroids and Comets Cassini-Huygens Chandra X-Ray Observatory Chandrayaan-1 Chang'e 1 Compare the Planets Dawn Deep Impact Earth Extrasolar Planets Genesis Hayabusa (MUSES-C) Hubble Space Telescope Jupiter Kaguya (SELENE) Lunar Reconnaissance Orbiter (LRO) Mars Mars Exploration Rovers Mars Express Mars Global Surveyor Mars Reconnaissance Orbiter Mercury MESSENGER Moon Near Earth Objects Neptune New Horizons New Horizons Digital Time Capsule Past Missions Phoenix Planetary Analogs Planetary Exploration Timelines Planetfest 2008 Pluto and Charon Pluto Top Ten Postcards from Venus Private Missions Rosetta Saturn Search for Extraterrestrial Intelligence SMART-1 SOHO Space Imaging Spitzer Space Telescope Stardust Trans-Neptunian Objects Ulysses Uranus Venus Venus Express Voyager Weekly Planetary Radio Trivia Contest

Space Topics: Search for Extraterrestrial Intelligence

The Search for Extraterrestrial Intelligence: A Short History

Part 3: A Blueprint for SETI

Morrison and Cocconi's short article became the blueprint for most of the SETI projects conducted in the past 40 years. The suggestion that electromagnetic signals were the most promising means for interstellar communications became the underlying assumption of all the searches, including the optical ones. The assumption that any alien signal would exhibit a Doppler drift has also been incorporated into all subsequent SETI projects, which invariably check for signals at drifting frequencies. But most important of all was their suggestion of a "universal" frequency that the aliens would most likely use for their transmissions. 1420 MHz has remained the most popular frequency used by SETI projects to this day.

The Water Hole The "Water Hole" - the magical frequency reange between 1420 MegaHertz and 1660 MegaHertz. Many SETI scientists believe it is the most promising band for a SETI search.

In later years another SETI pioneer, Hewlett Packard Vice President Bernard Oliver, added another magic frequency, 1662 KHz, the emission frequency of another very common molecule - OH, or hydroxyl. Hydrogen and hydroxyl combine to form H2O - water - the basic component of life, as we know it. Since 1662 KHz shares the advantages of 1420 MHz in being in a relatively "quiet" region of the spectrum, Oliver came to believe that the band between them held some unique promise for detecting an alien signal: "Surely the band lying between the resonances of the disassociation products of water is ideally situated and an uncannily poetic place for water-based life to seek its kind," Oliver wrote in 1971. "Where shall we meet? At the water-hole, of course!" Since then, the term "water hole" has been used to refer to searches at or around the hydrogen emission frequency.

Morrison and Cocconi's article was a call for action, and they hoped to put their theory to the test. Cocconi contacted Sir Bernard Lovell at the Jodrell Bank radio observatory, the largest dish in the world at the time, and suggested devoting telescope time to search for an extraterrestrial signal. Sir Bernard was, however, skeptical, and nothing came of the venture. The launch of the first radio search for an alien signal was left to others.

--Amir Alexander

Go to next chapter

Return to History of SETI main page