Copyright © 1997 by Dr. H. Paul Shuch, N6TXThe notion of humankind's uniqueness in the universe had been challenged by philosophers since before Copernican times. Nevertheless, it is only within the twentieth century that the existence of other technologically advanced civilizations in space has become a possibility accepted within the scientific establishment. Far more recently still has the feasibility of detecting such other civilizations entered mainstream thinking. Today, the search for evidence of other inhabited worlds is in full swing, thanks in part to the interest and expertise of the world's amateur radio operators, radio astronomers, and microwave experimenters. This Introduction tells you how you can join the search.
Executive Director, The SETI League, Inc.
PO Box 555, Little Ferry NJ 07643
from Proceedings of the AMSAT-NA Fifteenth Space Symposium, Toronto Canada, October 1997, 92-101.
The first scientific paper seriously contemplating surveying nearby stars for intelligently directed microwave signals was titled, boldly enough, "Searching for Interstellar Communications." It was written by Cornell physics professors Giuseppi Cocconi and Philip Morrison, and published in the British journal Nature in 1959. Unbeknownst to Morrison and Cocconi, as they were writing their pivotal paper, a young radio astronomer was preparing to perform the very experiment which they were describing. That scientist, Dr. Frank Drake, launched his Project Ozma search from the National Radio Astronomy Observatory (NRAO) facility at Green Bank, WV in 1960, ushering in the era of modern SETI.
Why do we suppose other civilizations might be detectable by their microwave radiation, and how will we know where to look for them? For that matter, why don't we simply look with our eyes? One problem is that stars typically outshine their unseen companions by about a billion to one. Seeking a planet orbiting another star is a little like trying to see a firefly perched on the rim of a searchlight. This is why the detection of extra-solar planets was not even possible until the current decade, and required the development of rather elaborate instrumentation. But at certain times, on certain frequencies, our Earth outshines the Sun a million to one.
The Earth is currently surrounded by a sphere of microwave radiation roughly fifty light years in radius, which is readily detectable over interstellar distances utilizing technology such as is today available to even amateur radio astronomers. This radiation, emanating primarily from our planet's UHF TV transmitters and long range search radars, would mark our planet as inhabited to any similar technological society within fifty light years. Within that range are found hundreds of stars, tens of which are sufficiently sun- like to probably host one or more habitable planets.
The distance over which we are detectable is limited only by the time since we first began transmitting these sufficiently strong signals in the appropriate frequency range. Fifty years from now, we will be detectable out to 100 light years distance. At that point our signals will have engulfed thousands of stars, including hundreds of potential life sites. With every successive doubling of elapsed time (out to 1,000 years or so), the number of civilizations which our radiation signature can potentially reach goes up by a factor of eight. Sooner or later, our signals may well reach distant ears.
SETI hypothesizes that other technological civilizations are similarly surrounded by a detectable sphere of microwave radiation, the radius of which will be limited only by how long such civilizations have possessed sufficiently advanced radio technology. We depend upon our ability to intercept and recognize (though not necessarily decode) such a radiation signature, to provide existence proof of other intelligent civilizations.
The problem with seeking incidental radiation is that the unknown factors exceed the known. We can only guess as to where physically to point our antennas, when to listen, and on what frequency. Interesting signals, after all, could be coming from any direction in the 4 pi steradians of space surrounding us. Other civilizations might well have harnessed any segment of the electromagnetic spectrum, and could be transmitting now, in the distant future, or in the deep past. Or maybe not at all. We just don't know.
The time dimension is resolved by starting to look now, and continuing until we detect something noteworthy. Given a great enough number of coordinated stations, effectively looking in all directions at once, we might resolve the pointing uncertainty. And we can narrow the search space in the frequency dimension by recognizing that particular range of frequencies which is least attenuated by planetary atmospheres and the interstellar medium. This, however, leaves us with most of the microwave spectrum, and much of the optical, as our likely range of frequencies.
Since there are no "wrong" frequencies to search, SETI has attempted to scan them all. One person's guess is as good as another's, so any frequency for which you can assemble a sufficiently sensitive telescope is fair game. Radio astronomers have long explored protected portions of the 406 MHz, 610 MHz, 1.42 GHz and 10.6 GHz bands, and I can think of no good reason why not to pursue the SETI dream in those spectral regions as well. And the world's radio amateurs have the capacity to scan a good many additional VHF, UHF and microwave frequencies, any of which may bear cosmic fruit.
The foregoing, however, applies only to the problem of scanning for incidental radiation from the distant civilization. What if another intelligent race were making a deliberate, concerted attempt to signal its presence to its interstellar neighbors? Is there a particular frequency, or range of frequencies, which would be self-evident to the receiving civilization? Can we narrow the search space?
Cocconi and Morrison thought so when they published their 1959 Nature article. They reasoned that 1420.40575 MHz, a natural emission frequency of neutral hydrogen atoms, was a good place to start looking for intelligently directed interstellar beacons. This frequency, which falls in the quietest part of the radio spectrum, is marked for all to see, by Nature herself. Everywhere you point a radio telescope, from anywhere in the Universe, you can hear this radiation, emanating from the one hydrogen atom which occupies each cubic centimeter or so of interstellar space. There is nothing geocentric about hydrogen radiation. Perhaps, it can be reasoned, selecting it for interstellar communication is a mark of intelligence, in and of itself.
Drake had arrived at this same conclusion independently of Morrison and Cocconi, and indeed set out to monitor a narrow band of frequencies encompassing the neutral hydrogen line (also known as H1) during his Project Ozma search. Today, nearly four decades later, the hydrogen line region still looks like a good bet to many SETI professionals. But the search need not stop at hydrogen.
Just a little ways higher up the microwave spectrum, around 1660 MHz, is another interesting spectral line, this one being the mark of radiation from interstellar hydroxyl (OH to the chemist). The late Dr. Bernard M. Oliver, who headed the now defunct NASA SETI effort, pointed out in the Cyclops Study (NASA's monumental 1971 research effort documenting the greatest radio telescope never built) that these two clearly discernible signposts occupy a prominent position in the quietest part of the sky. There are no other distinct radiation lines between them. And taken together, hydrogen and hydroxyl represent the disassociation products of water, the one solvent critical to all life processes known to us. This hydrogen-plus-hydroxyl-makes-water line of reasoning led Oliver and others to dub the region between their radiation lines the Water Hole, and to suggest that this may well be the natural interstellar communications band, defined for us all by Nature herself. "Where shall we meet other lifeforms?" asked Barney poetically. "At the water hole, where species have always gathered."
Fortunately for SETI, much classical radio astronomy research already goes on at the hydrogen line, the hydroxyl line, and the spectrum in between. Equipment for this frequency region is abundantly available, and much of it can be readily adapted to SETI use. From radio observatories at Ohio State and Harvard Universities in the US, from the Arecibo Observatory in Puerto Rico, from dishes in Argentina and Russia and Australia and Germany, cosmic anglers continue to cast their radio nets across the Water Hole, hoping to snag a big fish. There have been a few nibbles already. And some of those have been detected by radio amateurs.
There are indeed other likely "magic frequencies" which are being scanned for signals of possible intelligent extra-terrestrial origin, and once again, one person's guess is as valid as another's. Nevertheless, since many of the world's radio telescopes are already scanning the hydrogen line and its environs for natural astrophysical phenomena, it's a small step to make their receivers search for artificial signals as well. This is precisely what Drake's Project Ozma attempted to do in 1960.
Project Ozma must be considered the very first SETI study. It surveyed two nearby sun-like stars (Tau Ceti and Epsilon Eridani), for just a few weeks, at just one frequency, and detected no extra-terrestrial intelligent signals. Nevertheless, Ozma served as a model for dozens of later SETI endeavors, including The SETI League's own Project Argus sky survey.
The world's first professional SETI meeting was convened by Frank Drake at Green Bank in 1961. As the agenda for that conference, Drake drafted an equation for estimating the number of possible communicative technologies in the cosmos. He scribbled it on the blackboard, thus:
In the nearly four decades intervening, on the order of fifty different SETI projects have been conducted around the world, with frequency coverage extending throughout the microwave, millimeter-wave, and optical spectra. These searches have been attempted by Government agencies, educational institutions, non-profit scientific organizations, and, more recently, by amateurs.
Although no definitive proof of extra-terrestrial intelligence has yet been received, SETI has achieved scores of tantalizing hints that such signals might indeed exist. Many candidate signals have been attributed to terrestrial, aircraft and satellite interference, others to equipment malfunction and natural astrophysical phenomena, but about one candidate signal per year defies explanation. Since these signals have failed to repeat and have eluded our attempts at verification, we can draw no conclusion save that there is much to be learned about the universe we inhabit.
It's important to remember that SETI was emerging at a time when in the US, nationalism ruled science. Our government had set out in the late 1980's to become the world leader in subatomic particle research, and to do so, Congress had authorized funding for a multi-billion dollar Superconducting Supercollider. Construction was actually begun near Waxahatchee, TX, and some hundreds of millions of dollars expended, before more mundane projects (such as feeding and clothing the populace) began to vie for attention.
At about this time, NASA had a modestly funded but technologically ambitions SETI project under way from headquarters at the Ames Research Center, Mountain View, CA. Budgeted at $12.6 million annually (about 5 cents per American per year), NASA SETI kicked off on October 12, 1992, the 500th anniversary of Columbus' first voyage of discovery. The plan was to conduct a ten-year search.
Just one year later, in October of 1993, Congress pulled the plug on the Supercollider. Particle physics was deemed wasteful of our limited resources. And if particle physics was wasteful, the reasoning went, SETI was all the more so. We had been searching for a full year, argued Senator Richard Bryan (R - Nev.), and not one little green man had yet walked up and said 'Take me to your leader.' Which proved they do not exist.
In a single sweep of the pen, our elected leaders opted to cancel the Superconducting Supercollider, and NASA SETI as well. This makes good economic sense to some, since the cancellation of NASA SETI alone did indeed reduce the federal deficit . . . by all of 0.0006 percent!
Now enter Richard Factor, a New Jersey radio amateur (WA2IKL), science buff, and industrialist of more than modest means. Factor's company, Eventide Inc., was a leader in broadcast and studio electronics, aircraft navigation equipment, and a number of other high-tech products. For years Factor had toyed with the notion of building up his own amateur SETI station, and scanning the stars for signs of life. With the termination of NASA SETI, his resolve intensified.
"I got really mad when Congress killed SETI and the Superconducting Supercollider in the same year," says Factor. The Supercollider, with a price tag of $10 billion, was beyond his help. But SETI, he decided, could be salvaged. So he founded a non-profit, membership-supported educational and scientific corporation to privatize SETI. And he hired me, then an electronics professor in the Pennsylvania State University system, to run it. The SETI League was not my first taste of non-profit science, but it quickly became apparent that it would be the most challenging. For starters, it fell to me to decide exactly what role a citizen's group could play in resurrecting some component of the late NASA effort.
NASA SETI had been comprised of two distinct but complimentary research elements: a targeted search of nearby sun-like stars, and an all-sky survey for interesting signals of unknown origin. The former, which involves aiming powerful radio telescopes at likely candidate stars for long periods of time, is well suited to large, steerable dishes with their narrow beamwidths and high sensitivities. If we guess right as to which stars constitute likely candidates, the thinking goes, the targeted search will provide us with the greatest likelihood of immediate success. But since only a limited number of relatively nearby candidate stars is known to us, concentrating our search in their direction may cause us to miss an equally good star of which we happen to be unaware.
An all-sky survey, on the other hand, makes no a priori assumptions as to the most likely direction to explore. The sky survey attempts to sweep out the entire sky which can be seen from a given location. No antenna tracking is required, since it is the entire sky, rather than individual stars, which we seek to scan. While targeted search antennas must be constantly moved, sky survey radio telescopes are operated in meridian transit, or drift- scan mode, in which the experimenter never needs to aim the antennas. Rather, it is the Earth's rotation which turns them.
Shortly after its demise, NASA's late targeted search was resurrected by the non- profit California-based SETI Institute. This scientific organization had been the institutional home of many key players in NASA SETI, and they set about securing private sponsorship. Their aim was to utilize the same receivers and computer analysis tools they had designed for NASA, in a private search of the thousand nearest sun-like stars. They called their search Project Phoenix, having risen from the ashes of the late NASA SETI program.
Their success in this endeavor has been an inspiration to all who advocate the privatization of science. If they are as effective at science as they are at fundraising, the SETI Institute cannot miss. Project Phoenix employs some of the world's finest radio telescopes, aiming them sequentially at promising targets from a catalog of nearby sun-like stars. But since large antennas have quite narrow beamwidth, they see only a small portion of the sky at a given time. To sweep out the whole sky with such large antennas would consume inordinate amounts of time. A sky survey effort, as opposed to a targeted search, would be best performed with antennas of moderate size.
Smaller antennas can see more sky within their beam patterns, but have correspondingly less gain, thus more limited range. We achieve reasonable sensitivities through digital signal processing, the application of powerful computers to sift through the cosmic static for patterns which Nature cannot produce. But the antennas need to remain fixed on their targets for a relatively long time period, as the computers average out the background noise. With large antennas, this would require active tracking as the area of interest appears to drift east to west across the sky. Fortunately, when used in meridian transit mode, small antennas, with their relatively wide beamwidths, provide us with far greater signal acquisition time than do the larger antennas typically used for targeted searches.
The SETI League was actively attracting radio amateurs and microwave experimenters around the world, with the promise of some undefined great SETI project. And the sky survey approach seemed ideally suited to the community of amateur radio astronomers desiring to pursue SETI. So that is the aspect of SETI which Factor and his fledgling organization chose to pursue. A grass-roots effort ultimately involving thousands of amateur radio telescopes worldwide, the SETI League's Project Argus sky survey was initiated in April of 1996, with only five active stations. Within a year, the network had grown to 28 listening posts, and the League to 500 members in 26 countries. When fully deployed early in the next century, it is expected that Project Argus will provide (for the first time ever) real-time full-sky coverage, its thousands of antennas collectively looking in all directions at once, across all four pi steradians of space and time.
How can you join the Project Argus team? You might start by checking out The SETI League's extensive documentation on the World Wide Web, more than 700 documents exceeding 21 MBytes! Point your browser to http://www.setileague.org/. If you lack Web access, you can email your postal address to join_at_setileague_dot_org, or phone it in to the SETI League Membership Hotline, 1 (800) TAU-SETI, and introductory material will be sent to you through the mails. The SETI League's Technical Manual (ISBN 0-9650707-2-7) and other books will show you how to build your own amateur SETI station, for between a few hundred and a few thousand US Dollars.
Full sky coverage is not likely to occur overnight, but with a clear goal now articulated, it does stand a reasonable chance of becoming a reality. If signals are out there to be heard, I expect we will be able to detect and verify them, maybe even within my own lifetime. It takes only one verified signal to answer definitively a fundamental question which has haunted humankind since first we realized that the points of light in the night sky are other suns: Are We Alone?
If, on the other hand, after a generation or so of careful searching, we have still detected no evidence of other life, then we may be forced reluctantly to conclude that we are very much alone, the sole communicative species in our corner of the cosmos. Is not that discovery, too, worth the price of admission?
Either possibility, I am continually reminded, boggles the imagination.
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