Introduction for OSETI II
It has been three years since SPIE's first international conference on the Optical Search for Extraterrestrial Intelligence (SETI), and 35 years since Schwartz and Townes first proposed the use of lasers for interstellar communications. Last year, the chair thought it timely to arrange another conference on the subject, particularly as it was expected that The Columbus Optical SETI Observatory would be coming online by late 1996.
During the past three years, the NASA SETI Project, originally called the Microwave Observing Project (MOP), and then the High Resolution Microwave Survey (HRMS), has been privatized and transformed into Project Phoenix. It is now being left to the private sector to fund SETI research. In an attempt to save the "Big Ear" radiotelescope at The Ohio State University from demolition, Arthur C. Clarke has written that "The discoveries it has already made should act as an inspiration to the rising generation, and perhaps turn back the tide of anti-intellectualism which threatens to engulf the Western World in a new Dark Age of neo-barbarism.". Arthur couldn't have put it better about the forces at work in American society today that threaten this nation's scientific and technological inheritance.
The US Congress has essentially forbidden NASA to have anything to do with SETI. This is extremely ironic, however, since Dr. Dan Goldin, the NASA Administrator, has called for an extensive program to discover extrasolar planets. Dan Goldin has gone so far as to challenge the scientific and engineering communities to develop the means for imaging continents on earth-type planets around nearby stars. And, clearly, any capabilities for making such finely discriminating discoveries, as the SETI community well knows, sit right at the heart of any serious and mainstream SETI program. Furthermore, one can be confident that ETIs would have long ago developed these capabilities, and thus would be able to point-ahead target narrow laser beams towards nearby star systems.
Goldin was spurred to present this challenge by the exciting recent extrasolar planetary discoveries. These discoveries have begun the process by which one of the major unknowns in the famous Drake Equation (see the Introduction to the OSETI I Proceedings, SPIE Vol. 1867) fp - the probability that a star has a planetary system - can at last be more realistically estimated. Hopefully, this factor may soon be shown to be much nearer to unity than zero. Of course, the discovery of a microwave or optical ETI signal could short-circuit the immediate need to discover earth-type planets around other stars, and save much expense! At any rate, Goldin's challenge demonstrates that SETI, carried out with either private or public funding, is a perfectly natural and relatively trivial and inexpensive component of humankind's quest for knowledge and total space endeavors.
In the months preceding and following this OSETI II conference, thanks to the Hubble Space Telescope (HST) and other ground-based facilities such as the Lick Observatory, major discoveries have been reported on almost a weekly basis. These reports range from the discovery of extrasolar infrared and ultraviolet natural lasers, to planets around 51 Pegasus in the constellation of Pegasus, 70 Virginis in the constellation of Virgo, 47 Ursae Majoris in the constellation Ursa Major (the Big Dipper), a planet around the star HR 3522, the birth of new stars in M16 in the constellation of Serpens, 80 billion new galaxies in our universe, and the first direct image of a star (Betelgeuse). We live in truly exciting times, with profound implications for SETI, because, as these developments demonstrate, and as any SETI researcher knows, robust space exploration commits the broader scientific community to doing SETI in one form or another, whether they like it or not, know it or not, or fully appreciate it or not. Perhaps one day, after the HST has completed its mission of making major astronomical discoveries, it will be modified for doing optical SETI observations! For we cannot be sure that ETIs would employ ultraviolet, visible, or near-infrared lasers at wavelengths for which the atmosphere is essentially transparent.
So, assuming for the reasons stated that SETI efforts will continue in some form or other, and assuming that the recent discoveries will tend to give a higher value for N in the Drake Equation - i.e., the number of planets in the galaxy supporting intelligent life - the question then arises as to the most likely means by which mankind will first establish contact with an alien civilization.
Over the years, various approaches have been proposed for enabling "First Contact". A partial listing is given below:
1. Staying at home and communicating by:
2. To travel between star systems by:
(a) hibernating for slow, long voyages
The chair believes that lasers provide the most effective means of interstellar communications in the electromagnetic spectrum. Photons at x-ray and gamma-ray wavelengths are just too energetic, neutrinos and gravitational waves are poorly coupled to our antennas, and for the moment, exotic ideas for warp speed and subspace communications are in the realm of science fiction.
It is worth restating here the correct definition of the word "optical". In its modern usage, the word is employed as a superset term covering the entire electromagnetic spectrum from the far-infrared to the ultraviolet. "Optical" is not to be used as a term synonymous with "visible". This is to avoid confusion between the fields of astrophysics and photonics.
For this OSETI II conference, presentations were made on a variety of subjects. Many of these topics are complementary to those covered in the OSETI I conference. In these proceedings you will find papers on microwave SETI (MSETI), optical SETI (OSETI), extrasolar natural lasers and planets, the science educational aspects of SETI, and other related topics. What you will not find are discussions of UFOs, crop-circles and other paranormal manifestations, since most of the SETI community do not believe that they have a proper part to play in serious scientific discussions.
Last November, noted SETI Pioneer Dr. Barney Oliver passed away after many distinguished years of contributions to American technology. Barney, who had participated in the first OSETI conference, was probably proud of the fact that for most of the past 25 years, and ever since his famous Cyclops study, there has been relatively little discussion about the viability of the optical approach to SETI. The chair was looking forward to doing battle once again with Barney. But alas, that was not to be. Barney Oliver always had a fondness for "warm, fuzzy microwave photons". At the OSETI I conference, Barney had placed an upper limit to the ETI uplink gains usable at both microwave and optical frequencies due to the point-ahead targeting problem. His gain limitation was about 94 dB, while the chair thought that gains of 154 dB and higher would be possible for ETI civilizations, i.e., a factor one million times greater. It is mainly arguments about this issue that have led many in the SETI community to erroneously believe that the energy costs per photon were a lot higher in the optical regime. What matters more is the energy cost per received photon, and if we assume uplink gains of around 150 dB, then the energy cost per received microwave photon is actually higher than for optical photons! The bottom line for any link analysis is that it is usually a question of maximizing the signal-to-noise ratio (SNR) - not just operating with the lowest background noise.
One of us (SAK), has been very optimistic as to the Effective Isotropic Radiated Power (EIRP) laser capabilities of ETIs. But it should be realized that pulses of 1-ns duration with peak EIRPs that are instantaneously ten million times brighter than our sun, are still dim with respect to starlight when integrated over any significant length of time. In the millisecond pulse-width range, it is known that the naked eye requires about 70 photons for the brain to perceive a short flash. Even the seemingly extraordinary high ETI uplink "lighthouse beacon" pulsed EIRPs projected by the chair, do not produce sufficient photons at the naked eye to be detectable. Such a burst of photons represents only about 1% of the photons received from a typical solar-type star over a second, and hence is statistically insignificant for observations with the aided or unaided eye and in the presence of atmospheric turbulence.
In his paper, Dr. Paul Shuch makes the case that lasers are at least as good as microwaves for SETI-type communications. However, in some of the example link comparisons he presents, the efficacy of a 1-kW laser transmitter system is compared to that of a 1-MW microwave transmitter. On a watt-for-watt basis, this understates the case for lasers by 30 dB!
Perhaps the most important issue that will determine the choice of wavelength regime employed by ETI civilizations is the ability to sustain wideband communications over interstellar distances. For surely there must be a means of conveying a wideband channel other than a beacon. It is our view that the wavelength regime will be determined not just by SNR considerations. Before the next, and third OSETI conference, we would like to see extensive research efforts applied to comparing the levels of dispersion and scintillation effects across the entire microwave and optical spectrum and over ranges of several thousand light years. This should be done both in the galactic plane, where there is more dust and gas, and orthogonal to the plane. It is believed that the results of this study will determine whether ETIs use microwaves, millimeter waves, infrared, or visible lasers. It will most likely not be determined by "quiet" regions in the electromagnetic spectrum, the so-called "water hole", or harmonics of the water hole. The conclusions of these studies may signify the end to so-called narrow-band "magic wavelengths or frequencies". Rather, we could see the eventual emergence of relatively broadband "magic wavelength regimes" if ETIs are expected to employ very short beacon pulses to attract our attention, as first suggested by Dr. Monte Ross in 1965.
The mean distance between ETI civilizations in the Milky Way galaxy will likely affect the technology chosen by ETIs for SETI-type interstellar links. At this time we have no way of knowing this distance, but if it is less than several thousand light years, then the issue of optical attenuation need not be a factor governing this choice.
The chairs would particularly like to acknowledge a most generous donation from Arthur C. Clarke that enabled the cochair to participate in this conference. Arthur was the keynote speaker at the first optical SETI conference three years ago. He has indicated a desire to instrument for optical SETI the new 43-cm telescope that was donated by the Japanese government to the Arthur C. Clarke Centre for Modern Technologies in Sri Lanka. The telescope was dedicated last January. The chairs would also like to acknowledge the participation in this conference at very short notice of Drs. Geoffrey Marcy and Paul Butler, and Sean Colgan and Vladimir Strelnitski, et al. We can only apologize for not being able to obtain a paper on extrasolar natural ultraviolet lasers in Eta Carinae!
The chairs wish to thank the Project Phoenix team for hosting a reception and tour at the SETI Institute. We would like to acknowledge, with much thanks, Dr. Paul Shuch for the entertainment he provided prior to the workshop with his fine repertoire of SETI folk songs. The conference chairs gather that this was a first for SPIE. We also thank Dr. Monte Ross, the cochair for the OSETI I conference, for moderating the workshop.
An appendix is included, giving the latest version of "The Post-Detection SETI Protocol". The copyright to this document belongs to all of humankind, so readers are encouraged to copy this appendix and distribute it among friends, colleagues, colleges and schools.
The Columbus Optical SETI Observatory now has a presence on the World Wide Web. Optical SETI enthusiasts are encouraged to use this facility to keep up-to-date on developments in this field of scientific endeavor.
Dr. Stuart A. Kingsley, Chair
Dr. Guillermo A. Lemarchand, Cochair
Stop the presses! . . .
As this introduction was being finalized, we received word from David Blair at the University of Western Australia that he, his colleague Marlo Zadnik, and honors student Mark Lockett had just finished their first OSETI run, using the Perth-Lowell 64-cm aperture telescope. They have been looking for 1-us laser pulses with a cooled photomultiplier and a multichannel analyzer. They have observed 24 nearby stars, using both a wideband and a 1-nm-wide 572.8-nm filter. Unfortunately, still no aliens!
Copyright (c), 1996, SPIE