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Robotic SETI

April 27, 2012

"Have your people call my people," is one common rejoinder for characters on television situation comedies. In the search for extraterrestrial intelligence, the first handshake may be between their robots and our robots. There's also the possibility that this might happen after both intelligent civilizations have become extinct.

SETI, the search for extraterrestrial intelligence, has been conducted on the earth for about half a century. It started in 1960 with Project Ozma, an attempt by radio astronomer, Frank Drake, to listen for intelligent radio signals from two nearby stars, Tau Ceti and Epsilon Eridani.

Project Ozma used a radio telescope of the National Radio Astronomy Observatory (Green Bank, West Virginia) to search a small bandwidth around the "water hole," the 1.420 gigahertz (21 cm wavelength) emission line of interstellar hydrogen. This was thought to be an obvious place for communications when no standard communications frequencies are known.

Drake used a 26 meter telescope at the Green Bank site to make 150 hours of observations over a four-month period. No intelligent signals were detected, but this inspired other searches, such as John Krauss' Big Ear at Ohio State University, famous for the unexplained Wow! signal (see figure). Today, there's the on-again-off-again search by the SETI Institute using the Allen Telescope Array.

Figure caption

The Big Ear WOW! signal, recorded on August 15, 1977.

The time-varying signal intensity, 6EQUJ5, was recorded using a 36 level coding with the characters (space), 1..9, A..Z.
(Via Wikimedia Commons))

Such radio searches are one-way affairs; that is, we're just listening and hoping that the extraterrestrials are kind enough to send some very strong radio signals our way. Perhaps the extraterrestrials are not in a talking mood. Aside from the asymmetry of this scheme, there's the problem that we think that radio is the best means for such extraterrestrial contact.

I'm reminded of the golden hammer rule; namely, "When all you have is a hammer, everything looks like a nail." Will radio even be used a hundred years from now, or will it have been replaced by something much better? A hundred years from now our descendants might be comparing their technology to radio in the same way that we compare radio to smoke signals.

Other communication schemes have been proposed. The laser, of course, is one of these, and one of its inventors, Charles Townes, proposed optical SETI as early as 1983.[2] Even earlier than that, in 1960, Ronald N. Bracewell proposed sending physical probes in search of extraterrestrial life.[3]

Google Android Robot

A robot almost everyone can relate to.

Would an E.T. of today phone home on an Android phone?

There are about 300 million users of Android devices.

(Via Wikimedia Commons))

Several aspects of a successful robotic SETI program are covered in an article by Penn State professor of electrical engineering, John D. Mathews, scheduled to appear in the Journal of the British Interplanetary Society.[4] Mathews argues for a mission that takes into consideration the economical realities of civilizations, realities that he thinks are also shared by extraterrestrials.

Mathews thinks that such probes should start as dual-purposed objects that would be designed to clear debris from our solar system. I mentioned the dangers that Earth faces from rogue asteroids in a previous article (Asteroid Deflection, April 19, 2012). Such autonomous, self-replicating robots can reproduce from materials found in our solar system to launch into the vicinity of other stars.[4]

A recent numerical simulation of exploration by such SETI robots gives some interesting insights into the probability of making contact.[5] The model assumes that a probe will have a lifetime of 50 million years, and there's a contact window of about a million years. If there were between a hundred and a thousand civilizations doing robotic probing, then we would have heard from one of these if they were within a thousand parsecs of the Earth. The extent of the Milky Way Galaxy is about 35,000 parsecs.


  1. Early SETI: Project Ozma, Arecibo Message, SETI Institute Web Site.
  2. C. H. Townes, "At what wavelengths should we search for signals from extraterrestrial intelligence?" Proc. Natl. Acad. Sci., vol. 80, no. 4 (February 1, 1983), pp. 1147-1151.
  3. R. N. Bracewell, "Communications from Superior Galactic Communities," Nature, vol. 186, no. 4726 (May 28, 1960), pp. 670-671 (paywalled PDF with no free abstract).
  4. Andrea Elyse Messer, "Finding ET may require giant robotic leap," Penn State University Press Release, April 18, 2012.
  5. Carlos Cotta and Álvaro Morales, "A Computational Analysis of Galactic Exploration with Space Probes: Implications for the Fermi Paradox," arXiv Preprint Server, July, 2, 2009.

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