Guest EditorialThe NASA Astrobiology Conference in April, 2008 had as one of its topics, Future SETI: Technologies, Techniques and Strategies. Its premise is that after five decades of negative results from radio and optical SETI searches, there should be new approaches to the problem like detecting the biosignature of an extrasolar planet. This premise regarding SETI is not supported by reality.
The search for an extraterrestrial civilization is one of the most intellectually stimulating and potentially rewarding pursuits open to humanity. As we approach five decades since the 1959 groundbreaking paper by Giuseppe Cocconi and Philip Morrison, Searching for Interstellar Communications, much discussion has taken place on how to detect interstellar signals. In actual fact, very little systematic exploration has been performed. The NASA SETI project and the use of the NASA targeted SETI signal processing equipment by a private organization over a ten year period was especially disappointing in what it accomplished.
Many ideas have been put forward speculating on the existence of extraterrestrial civilizations, their number in the galaxy and their longevity. For those civilizations that become technological and do not self destruct, it is reasonable to assume that some number reach long lifetimes and are still scientifically curious. An interstellar beacon, which has as its sole purpose communication with other contemporary technological civilizations in the galaxy, is quite plausible under these circumstances.
What would be the motivation to construct such a beacon? Perhaps there is an altruistic code in the galaxy to preserve the history of all civilizations, past and present? Perhaps there would be interest in contacting new technological civilizations like us, knowing that there is a time window (hundreds of years) after the the discovery of radio when some societies disintegrate because of sociological and environmental factors. In all likelihood, we would not be the first civilization that they have made contact with, thus finding one could be the gateway to many contacts. What could they expect to learn from finding one more? They may know a lot and have great understanding of science but the Earth's civilization with its unique biology and history will be a new one for them to put into the larger context of life in the universe. Maybe they will ask for pictures and sounds from our culture? Maybe they will ask for detailed data on our solar system? This seems far more practicable and feasible than sending out an armada of spaceships to explore other star systems. In a way, we would be their interstellar space probes.
There is another possibility in the quest to find an extraterrestrial technological civilization. Might we detect their internal communication signals (leakage), like our TV or radar? This seems like an almost hopeless proposition and is beyond our current technological capabilities. Let twenty second century SETI researchers work on detecting leakage, should our efforts in this century prove fruitless.
When one considers all the concatenated probabilities connected with the formation of planet Earth, its composition, its stable environment over geological timescales that allowed complex life to flourish, the inescapable conclusion is that millions of sun-like stars will have to be examined to find one that is transmitting an artificial signal. That means the search volume of space could extend from one to two thousand light years. The NASA Kepler Mission, which is scheduled for launch in 2009, will for the first time give us hard empirical data on the number of Earth-like planets in habitable zones, their orbital stability in multiple star systems, and the types of stars that have them. This will be quite important in bounding the SETI search space.
Recently, the NASA Astrobiology Institute sponsored studies of M stars as potential sites where complex lifeforms could exist. Even though M stars comprise about two thirds of all stars in the galaxy, which makes them attractive from a numbers standpoint, they are however poor candidates as SETI targets for the following reason.
M type stars have an effective temperature of 1/2 and a radius of 1/3 that of our Sun. Using a basic model, one can calculate the habitable zone, the annulus around a star in which stellar flux is sufficient to allow liquid water to exist. This puts the M star planet at about 0.1 AU and it may well be tidally locked.
There are a multitude of reasons why biology, let alone a technological civilization, would be ill-suited to exist on such a planet. Imagine a tidally locked Earth orbiting a M star where half the Earth, say from 0 to 180 degrees west longitude, is in perpetual darkness and permanently frozen down to 200 degrees below zero centigrade. I trust none of us would be living in California.
If a targeted search is the strategy of choice and detection sensitivity is essential, a targeted search of millions of stars would take centuries to complete. And even if one of these stars is indeed broadcasting, detection could be missed because our detection sensitivity was just not good enough, or interstellar scintillation degraded the signal during the observation time frame, or the observation is not coincident with the duty cycle of the beacon, or we are not sensitive to the particular type of signal structure being transmitted.
Based on the above considerations, it is logical (logic flows from causality) to expect that our galactic colleagues will make the detection problem for the contact as simple and straightforward as possible. Universality of the laws of physics and the logic of mathematics will govern their strategy to maximize the probability of detection.
My own career with the NASA SETI project included 15 years working with Dr. Kent Cullers (now living in South Africa), the leading expert in the world on SETI signal detection. I never did stop working on the detection problem. During the 1990's, I organized a team to construct a radio telescope dedicated to SETI research. The team included Professor Frank Drake.
When I was with the NASA SETI project, one of the scientists told us that there really has not been a new idea with SETI in the last twenty years. Maybe this will all change? I have come up with new thinking in how the interstellar communication link would be achieved. Something has been overlooked. If my ideas are scientifically sound, it is quite possible to make a detection within a decade using existing telescopes and signal processing capabilities.
The expectation is that the contact/acquisition signal will be an address (pointer), like in the C programming language. It will direct contactees to where the actual communication channel is located. The exact frequency channel of the beacon transmitter may be known. Our astronomical capabilities might be insufficient to receive the text of the extraterrestrial transmission.
The charter of NASA includes a statement, the expansion of human knowledge of phenomena in the atmosphere and space. Some of us who were with NASA for the SETI inauguration on Oct 12,1992 (500th anniversary of Columbus discovering the Americas) remember the worldwide interest and excitement created by what the agency was doing. Can we not rekindle this exploration spirit with a new generation of Americans?
NASA already has in place many of the resources needed to begin the search. The NASA SETI project was based on the 1977 NASA SP-419 report. See the conclusions from the report [NASA sp-419] which are still valid today. The 1993 congressional mandate to end United States funding for SETI is no longer in effect. Proposals for SETI grants are now being accepted by NASA and the NSF, but NASA is the proper federal agency to carry out a comprehensive search. The agency should form a small exploratory group, uninhibited by past orthodoxy, and take a fresh look at the search for extraterrestrial intelligence.
Disclaimer: The opinions expressed in editorials are those of the individual authors, and do not necessarily reflect the position of The SETI League, Inc., its Trustees, officers, Advisory Board, members, donors, or commercial sponsors.
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