by Paul Gilster | Jul 21, 2017 | Astrobiology and SETI |
Yesterday’s post dwelt on an article by Steven Johnson in the New York Times Magazine that looked at the issue of broadcasting directed messages to the stars. The article attempted a balanced look, contrasting the goals of METI-oriented researchers like Douglas Vakoch with the concerns of METI opponents like David Brin, and fleshing out the issues through conversations with Frank Drake and anthropologist Kathryn Denning. Johnson’s treatment of the issue prompted a response from a number of METI critics, as seen below. The authors, all of them prominent in SETI/METI issues for many years, are listed at the end of the text.
We thank Steven Johnson for his thoughtful New York Times Magazine article, which makes it clear that there are two sides to the METI issue. We applaud his idea that humankind needs a mechanism for decision-making on long-term issues that could threaten our future.
As Johnson implies, deliberately calling ourselves to the attention of a technological civilization more advanced than ours is one of those issues. What we do now could affect our descendants.
As Johnson asks, who decides? Without an agreed approach, the decision to transmit might be made by whoever has a sufficiently powerful transmitter.
Astronomers have given us an additional reason for addressing this question: the discovery of thousands of planets in orbit around other stars, increasing the probability that life and intelligence have evolved elsewhere in our galaxy.
METI is not scientific exploration. It is an attempt to provoke a reaction from an alien civilization whose capabilities and intentions are not known to us.
The most likely motivation for alien intervention is not a wish to exploit Earth’s territory or resources, but the potential threat posed by a new space-faring civilization — us. Scientists and engineers already are designing Humankind’s first unmanned interstellar probes. Some might be visiting nearby stars less than a century from now.
Image: Taken by the Advanced Camera for Surveys on the Hubble Space Telescope, this image shows the core of the great globular cluster Messier 13, to which a message was beamed in 1974. Credit: ESA/Hubble and NASA.
Though altruism may be a noble goal, human history suggests that it rarely extends beyond one’s own species. We have not been very altruistic toward dolphins, whales, or chimpanzees.
What mechanism can we devise for what Johnson calls global oversight of METI? In the 1970s conferences at Asilomar assessed dangers from the then theoretical notion of genetic engineering. The resulting compromises improved laboratory safety while allowing continued research in this field under an agreed set of rules.
In the 1980s, some of us proposed a first step toward agreed rules through the document known informally as the First SETI Protocol, which calls for consultations before responding to a detected alien signal. (That protocol has been endorsed by most SETI researchers, but has not been adopted by government agencies.) An attempt to gain consensus on a second protocol calling for consultations before the transmission of powerful, human-initiated signals foundered on a basic disagreement that is mirrored in today’s METI debate.
Seventeen years ago, the International Academy of Astronautics presented a proposal to the United Nations for an international decision-making process for sending such communications. The U.N. noted the report and filed it.
Plans to send powerful targeted messages to nearby solar systems have brought this issue back to our attention. The underlying issue has not changed. As renowned Chinese science fiction writer Cixin Liu wrote, “I’ve always felt that extraterrestrial contact will be the greatest source of uncertainty for humanity’s future.” Let’s address that issue as rationally as we can.
Gregory Benford, astrophysicist and science fiction author
James Benford, radio astronomer
David Brin, astrophysicist and science fiction author
Catharine A. Conley, NASA Planetary Protection Officer
John Gertz, former chairman of the SETI Institute
Peter W. Madlem, former board member of the SETI Institute
Michael Michaud, former diplomat, author
John Rummel, former Director, NASA Planetary Protection Office
Dan Werthimer, radio astronomer
by Paul Gilster | Jul 20, 2017 | Astrobiology and SETI |
If we were to send a message to an extraterrestrial civilization and make contact, should we assume it would be significantly more advanced than us? The odds say yes, and the thinking goes like this: We are young enough that we have only been using radio for a century or so. How likely is it that we would reach a civilization that has been using such technologies for an even shorter period of time? As assumptions go, this one seems sensible enough.
But let’s follow it up. In an interesting piece in the New York Times Magazine, Steven Johnson makes the case this way: Given the age of the universe, almost 14 billion years, that means it would have taken 13,999,999,900 years before radio communications became a factor here on Earth. Now let’s imagine a civilization that deviates from our own timeline of development by just one tenth of one percent. If they are more advanced than us, they will have been using technologies like radio and its successors for 14 million years.
Assumptions can be tricky. We make them because we have no hard data on any civilization outside our own. About this one, we might ask: Why should there be any universal ‘timeline’ of development? Are there ‘plateaus’ when the steep upward climb of technological change goes flat? Soon we have grounds for an ever deeper debate. What constitutes civilization? What constitutes intelligence, and is it necessarily beneficial, or a path toward extinction?
Image: The Arecibo Observatory in Puerto Rico, from which a message was broadcast to the globular cluster M13 in 1974.
Airing out the METI Debate
I want to commend Johnson’s piece, which is titled “Greetings, E.T. (Please Don’t Murder Us.” As you can fathom from the title, the author is looking at our possible encounter with alien civilizations in terms not of detection but of contact, and that means we’re talking METI — Messaging Extraterrestrial Intelligence. What I like about Johnson’s treatment is that he goes out of his way to talk to both sides of a debate known more for its acrimony than its enlightenment. Civility counts, because both sides of the METI issue need to listen to each other. And the enemies of civilized discussion are arrogance and facile assertion.
It was Martin Ryle, then Astronomer Royal of Britain, who launched the first salvo in the METI debate in response to the Arecibo message of 1974, asking the International Astronomical Union to denounce the sending of messages to the stars. In the forty years since, about a dozen intentional messages have been sent. The transmissions of Alexander Zaitsev from Evpatoria are well known among Centauri Dreams readers (see the archives). Douglas Vakoch now leads a group called METI that plans to broadcast a series of messages beginning in 2018. The Breakthrough Listen initiative has also announced a plan to design the kind of messages with which we might communicate with an extraterrestrial civilization.
All of this will be familiar turf for Centauri Dreams readers, but Johnson’s essay is a good refresher in basic concepts and a primer for those still uninitiated. He’s certainly right that the explosion of exoplanet discovery has materially fed into the question of when we might detect ETI and how we could communicate with it. It has also raised questions of considerable significance about the Drake Equation; specifically, about the provocative term L, meant to represent the lifespan of a technological civilization.
Johnson runs through the Fermi question — Where are they? — by way of pointing to L’s increasing significance. After all, when Frank Drake drew up the famous equation and presented it at a 1961 meeting at Green Bank (the site of his Project Ozma searches), no one knew of a single planet beyond our Solar System. Now we’re learning not just how frequently they occur but how often we’re likely to find planets in the habitable zone around their stars. The numbers may still be rough, but they’re substantial. There are billions of habitable zone planets in the galaxy, so the likelihood of success for SETI would seem to rise.
And if we continue to observe no other civilizations? The L factor may be telling us that there is a cap to the success of intelligent life, a filter ahead of us in our development through which we may not pass, whether it be artificial intelligence or nuclear weaponry or nanotechnology. METI’s critics thus worry about planet-wide annihilation, and wonder if a limiting factor for L, at least for some civilizations, might be interactions with other, more advanced cultures. Far better for our own prospects if the ‘filter’ is behind us, perhaps in abiogenesis itself.
Hasn’t our own civilization already announced its presence, not just through an expanding wavefront of old TV and radio shows but also through the activity of our planetary radars, and the chemistry of our atmosphere? After all, even at our level of technology, we’re closing in on the ability to study the atmospheres of Earth-class planets around other stars. If this is the case, are we simply being watched from afar because we’re just one of many civilizations, and perhaps not one worth communicating with? METI proponents will argue that this is another reason to send a message: Announce that, at long last, we are ready to talk.
The counter-argument runs like this: A deliberately targeted message is a far different thing than the detection of life-signs on a distant planet. The targeted message is a wake-up call, saying that we are intent on reaching the civilizations around us and are beginning the process. Passive signal leakage is one thing; targeting a specific star implies an active level of interest. And the problem is, we have no way of knowing how an alien culture might respond.
Procedures for Consensus
In his article, Johnson is well served by the interviews he conducted with with Frank Drake (anti-METI, but largely because he would prefer to see METI funding applied to conventional SETI); METI proponent and former SETI scientist Vakoch; anti-METI spokesman and author David Brin; and anthropologist Kathryn Denning, who supports broad consultation on METI. Johnson does an admirable job in summarizing the key questions, one of which is this: If we are dealing with technologies whose use has huge consequences, do individuals and small groups have the right to decide when and how these technologies should be used?
I think Johnson hits the right note on this matter:
Wrestling with the METI question suggests, to me at least, that the one invention human society needs is more conceptual than technological: We need to define a special class of decisions that potentially create extinction-level risk. New technologies (like superintelligent computers) or interventions (like METI) that pose even the slightest risk of causing human extinction would require some novel form of global oversight. And part of that process would entail establishing, as Denning suggests, some measure of risk tolerance on a planetary level. If we don’t, then by default the gamblers will always set the agenda, and the rest of us will have to live with the consequences of their wagers.
Easier said than done, of course. How does global oversight work? And how can we bring about a discussion that legitimately represents the interests of humanity at large?
Consultation also meets an invariable response: You can talk all you want, but someone is going to do it anyway. In fact, various groups already have. In any case, when have you ever heard of human beings turning their back on technological developments? For that matter, how often have we deliberately chosen not to interact with another society? Johnson adds:
But maybe it’s time that humans learned how to make that kind of choice. This turns out to be one of the surprising gifts of the METI debate, whichever side you happen to take. Thinking hard about what kinds of civilization we might be able to talk to ends up making us think even harder about what kind of civilization we want to be ourselves.
The METI debate is robust and sometimes surprising because of what doesn’t get said. Under the frequent assumption that human civilization is debased, we assume an older culture will invariably have surmounted its own challenges to become enlightened and altruistic. Possibly so, but without data, how can we know that other civilizations may not be more or less like ourselves, in having the capacity for great achievement as well as the predatory instincts that can cause them to turn on themselves and on others? Is there a way of living with expansive technologies while remaining a flawed and striving culture that can still make huge mistakes?
We can’t know the characteristics of any civilization without data, which is why a robust SETI effort remains so crucial. As for METI, I’ll be publishing tomorrow a response to Johnson’s article from a group of METI’s chief opponents exploring these and other points.
by Paul Gilster | Jul 19, 2017 | Exoplanetary Science |
Frank Elmore Ross (1874-1960), an American astronomer and physicist, became the successor to E. E. Barnard at Yerkes Observatory. Barnard, of course, is the discoverer of the high proper motion of the star named after him, alerting us to its proximity. And as his successor, Ross would go on to catalog over 1000 stars with high proper motion, many of them nearby. Ross 128, now making news for what observers at the Arecibo Observatory are calling “broadband quasi-periodic non-polarized pulses with very strong dispersion-like features,” is one of these, about 11 light years out in the direction of Virgo.
Any nearby stars are of interest from the standpoint of exoplanet investigations, though thus far we’ve yet to discover any companions around Ross 128. An M4V dwarf, Ross 128 has about 15 percent of the Sun’s mass. More significantly, it is an active flare star, capable of unpredictable changes in luminosity over short periods. Which leads me back to that unusual reception. The SETI Institute’s Seth Shostak described it this way in a post:
What the Puerto Rican astronomers found when the data were analyzed was a wide-band radio signal. This signal not only repeated with time, but also slid down the radio dial, somewhat like a trombone going from a higher note to a lower one.
And as Shostak goes on to say, “That was odd, indeed.”
It’s this star’s flare activity that stands out for me as I look over the online announcement of its unusual emissions, which were noted during a ten-minute spectral observation at Arecibo on May 12. Indeed, Abel Mendez, director of the Planetary Habitability Laboratory at Arecibo, cited Type II solar flares first in a list of possible explanations, though his post goes on to note that such flares tend to occur at lower frequencies. An additional novelty is that the dispersion of the signal points to a more distant source, or perhaps to unusual features in the star’s atmosphere. All of this leaves a lot of room for investigation.
We also have to add possible radio frequency interference (RFI) into the mix, something the scientists at Arecibo are examining as observations continue. The possibility that we are dealing with a new category of M-dwarf flare is intriguing and would have obvious ramifications given the high astrobiological interest now being shown in these dim red stars.
All of this needs to be weighed as we leave the SETI implications open. The Arecibo post notes that signals from another civilization are “at the bottom of many other better explanations,” as well they should be assuming those explanations pan out. But we should also keep our options open, which is why the news that the Breakthrough Listen initiative has now observed Ross 128 with the Green Bank radio telescope in West Virginia is encouraging.
No evidence of the emissions Arecibo detected has turned up in the Breakthrough Listen data. We’re waiting for follow-up observations from Arecibo, which re-examined the star on the 16th, and Mendez in an update noted that the SETI Institute’s Allen Telescope Array had also begun observations. Seth Shostak tells us that the ATA has thus far collected more than 10 hours of data, observations which may help us determine whether the signal has indeed come from Ross 128 or has another source.
“We need to get all the data from the other partner observatories to put all things together for a conclusion,” writes Mendez. “Probably by the end of this week.”
Or perhaps not, given the difficulty of detecting the faint signal and the uncertainties involved in characterizing it. If you’re intrigued, an Arecibo survey asking for public reactions to the reception is now available.
I also want to point out that Arecibo Observatory is working on a new campaign to observe stars like Ross 128, the idea being to characterize their magnetic environment and radiation. One possible outcome of work like that is to detect perturbations in their emissions that could point to planets — planetary magnetic fields could conceivably affect flare activity. That’s an intriguing way to look for exoplanets, and the list being observed includes Barnard’s Star, Gliese 436, Ross 128, Wolf 359, HD 95735, BD +202465, V* RY Sex, and K2-18.
A final note: Arecibo is now working with the Red Dots campaign in coordination with other observatories to study Barnard’s Star, for which there is some evidence of a super-Earth mass planet. More on these observations can be found in this Arecibo news release.
by Paul Gilster | Jul 18, 2017 | Astrobiology and SETI |
Yesterday I made mention of the Schwartz and Townes paper “Interstellar and Interplanetary Communication by Optical Masers,” which ran in Nature in 1961 (Vol. 190, Issue 4772, pp. 205-208). Whereas the famous Cocconi and Morrison paper that kicked off radio SETI quickly spawned an active search in the form of Project Ozma, optical SETI was much slower to develop. The first search I can find is a Russian project called MANIA, in the hands of V. F. Shvartsman and G. M. Beskin, who searched about 100 objects in the early 1970s, finding no significant brightness variations within the parameters of their search.
If you want to track this one down, you’ll need a good academic library, as it appears in the conference proceedings for the Third Decennial US-USSR Conference on SETI, published in 1993. Another Shvartsman investigation under the MANIA rubric occurred in 1978. Optical SETI did not seem to seize the public’s imagination, perhaps partially because of the novelty of communications through the recently discovered laser. We do see several optical SETI studies at UC-Berkeley’s Leuschner Observatory and Kitt Peak from 1979 to 1981, the work of Francisco Valdes and Robert Freitas, though these were searches for Bracewell probes within the Solar System rather than attempts to pick up laser transmissions from other star systems.
Image: Harvard’s Paul Horowitz, a key player in the development of optical SETI. Credit: Harvard University.
This was an era when radio searches for extraterrestrial technology had begun to proliferate, but despite the advocacy of Townes and others (and three conferences Townes helped create), it wasn’t until the 1990s that optical SETI began to come into its own. Charles Townes himself was involved in a search for laser signals from about 300 nearby stars in the ’90s, using the 1.7-meter telescope on Mt. Wilson and reported on at the 1993 conference. Stuart Kingsley began an optical SETI search using the 25-centimeter telescope at the Columbus Optical SETI Observatory (COSETI) in 1990, while Gregory Beskin searched for optical signals at the Special Astrophysical Observatory run by the Russian Academy of Sciences in the Caucasus in 1995.
Optical SETI’s advantages were beginning to be realized, as Andrew Howard (Caltech) commented in a 2004 paper:
The rapid development of laser technology since that time—a Moore’s law doubling of capability roughly every year—along with the discovery of many microwave lines of astronomical interest, have lessened somewhat the allure of hydrogen-line SETI. Indeed, on Earth the exploitation of photonics has revolutionized communications technology, with high-capacity fibers replacing both the historical copper cables and the long-haul microwave repeater chains. In addition, the elucidation (Cordes & Lazio 1991) of the consequences to SETI of interstellar dispersion (first seen in pulsar observations) has broadened thinking about optimum wavelengths. Even operating under the prevailing criterion of minimum energy per bit transmitted, one is driven upward to millimetric wavelengths.
In the late 90’s, the SETI Institute, as part of a reevaluation of SETI methods, recommended and then co-funded several optical searches including one by Dan Werthimer and colleagues at UC Berkeley and another by a Harvard-Smithsonian team including Paul Horowitz and Andrew Howard. The Harvard-Smithsonian group also worked in conjunction with Princeton University on a detector system similar to the one mounted on Harvard’s 155-centimeter optical telescope. A newer All-Sky Optical SETI (OSETI) telescope, set up at the Oak Ridge Observatory at Harvard and funded by The Planetary Society, dates from 2006.
Image: Dan Werthimer, chief scientist at the Berkeley SETI Research Center. Credit: UC-Berkeley.
At Berkeley, the optical SETI effort is led by Werthimer, who had built the laser detector for the Harvard-Smithsonian team. Optical SETI efforts from Leuschner Observatory and Lick Observatory were underway by 1999. Collaborating with Shelley Wright (UC Santa Cruz), Remington Stone (UC Santa Cruz/Lick Observatory), and Frank Drake (SETI Institute), the Berkeley group has gone on to develop new detector systems to improve sensitivity. As I mentioned yesterday, UC-Berkeley’s Nate Tellis, working with Geoff Marcy, has analyzed Keck archival data for 5,600 stars between 2004 and 2016 in search of optical signals.
Working in the infrared, the Near-Infrared Optical SETI instrument (NIROSETI) is designed to conduct searches at infrared wavelengths. Shelley Wright is the principal investigator for NIROSETI, which is mounted on the Nickel 1-meter telescope at Lick Observatory, seeing first light in March of 2015. The project is designed to search for nanosecond pulses in the near-infrared, with a goal “to search not only for transient phenomena from technological activity, but also from natural objects that might produce very short time scale pulses from transient sources.” The advantage of near-infrared is the decrease in interstellar extinction, the absorption by dust and gas that can sharply impact the strength of a signal.
Image: Shelley Wright, then a student at UC-Santa Cruz, helped build a detector that divides the light beam from a telescope into three parts, rather than just two, and sends it to three photomultiplier tubes. This arrangement greatly reduces the number of false alarms; very rarely will instrumental noise trigger all three detectors at once. The three-tube detector is in the white box attached here to the back of the 1-meter Nickel Telescope at Lick Observatory. Credit: Seth Shostak.
I might also mention METI International’s Optical SETI Observatory at Boquete, Panama. The idea is to put the optical SETI effort in context. With the SETI Institute now raising money for its Laser SETI initiative — all-sky all-the-time — the role of private funding in making optical SETI happen is abundantly clear. And now, of course, we also have Breakthrough Listen, which in addition to listening at radio wavelengths at the Parkes instrument in Australia and the Green Bank radio telescope in West Virginia, is using the Automated Planet Finder at Lick Observatory to search for optical laser transmissions. Funded by the Breakthrough Prize Foundation, the project continues the tradition of private funding from individuals, institutions (the SETI Institute) and organizations like The Planetary Society to get optical SETI done.
by Paul Gilster | Jul 17, 2017 | Astrobiology and SETI |
The Laser SETI campaign we looked at on Friday is one aspect of a search for intelligent life in the universe that is being addressed in many ways. In addition to optical methods, we look of course at radio wavelengths, and as we begin to characterize the atmospheres of rocky exoplanets, we’ll also look for signs of atmospheric modification that could indicate industrial activity. But we have to be careful. Because SETI looks for evidence of alien technology, it is a search for civilizations about whose possible activities we know absolutely nothing.
So we can’t make assumptions that might blind us to a detection. Getting the blinders off also means extending our reach. If successful, the Laser SETI project will do two things we haven’t been able to do before — it will scan the entire sky and, because it is always on, it will catch optical transients we are missing today, and tell us whether any of these are repeating.
In radio terms, think of the famous WOW! signal of 1977, detected at Ohio State University’s Big Ear radio telescope. Seeming to come out of the constellation Sagittarius, it fit our ideas of what an extraterrestrial signal could look like, but we can’t draw any conclusions because we’ve never seen it again. If the signal intrigues you, Robert Gray’s book The Elusive WOW (Palmer Square, 2011) goes into it in great depth, including Gray’s 1987 and 1989 attempts to find it. Gray would search again in the mid 90’s using the Very Large Array, and again in 1999 with the University of Tasmania’s Mount Pleasant Radio Observatory, with null results.
The Elusive WOW is a splendid page-turner that captures the drama of the hunt. It also reminds us how frustrating a transient can be — here today, gone in moments, never seen again. Did the WOW signal reappear at some time that we weren’t pointing our instruments at it? Is it repeating on some schedule we haven’t figured out?
All-sky surveys like Laser SETI weren’t on the mind of Giuseppe Cocconi and Philip Morrison when they wrote their ground-breaking paper “Searching for Interstellar Communications” in Nature (1959), one that is mostly commonly cited as launching SETI. But for optical SETI’s origins, we can look back with equal admiration at R. N. Schwartz and Charles Townes’ “Interstellar and Interplanetary Communication by Optical Masers,” which ran two years later in the same journal. The author’s vision encapsulates the idea:
We propose to examine the possibility of broadcasting an optical beam from a planet associated with a star some few or some tens of light-years away at sufficient power-levels to establish communications with the Earth. There is some chance that such broadcasts from another society approximately as advanced as we are could be adequately detected by present telescopes and spectrographs, and appropriate techniques now available for detection will be discussed. Communication between planets within our own stellar system by beams from optical masers appears a fortiori quite practical.
Image: Charles Hard Townes, at the National Institute of Biomedical Imaging and Bioengineering’s 5th Anniversary Symposium, held in June 2007. Credit: NIBIB.
Optical SETI Scenarios
We saw Friday that a petawatt laser of the kind that has been built at Lawrence Livermore National Laboratory could be transformed into an optical SETI beacon, working in conjunction with a huge mirror like that found on our largest telescopes. Indeed, the Sun can be outshone by a factor of 10,000, a bright and, one would assume, obviously artificial beacon. But the complexities involved in targeting another star — and aiming the beam to lead the moving target, one that will be many light years away, make targeted laser beacons difficult.
Surely the challenges of laser beacons — not to mention their cost — could be overcome by advanced civilizations, although the idea of a less targeted beacon seems to make more sense; i.e., a beacon that sweeps a region of the sky on a recurrent basis, assuming the intent here is simply to announce the presence of the extraterrestrial civilization as widely as possible. But perhaps it’s much more likely that, if we do detect a laser signal from another civilization, it will be in the form of a chance interception of a technology at work.
Image: The power of laser technology even today. Credit: Eliot Gillum/SETI Institute.
Detecting communications within an exoplanetary system presents serious problems of geometry, given that these optical beams would be broadcast to specific targets and are unlikely to be pointing by chance at the Earth. But there is a scenario that could work: We’ve learned all about exoplanet detection through planetary transits from the Kepler mission. A planetary system that was co-planar with our own could produce a communications beam between its own planets that swept past us with each orbital revolution. Even then, the target planet would likely absorb enough of the signal that detection would be unlikely.
But there are other kinds of detections. James Guillochon and Abraham Loeb have looked at the possibility that beaming to interstellar sailcraft would produce leakage that might be observable to our detectors (see SETI via Leakage from Light Sails in Exoplanetary Systems). Both interplanetary as well as interstellar transportation systems leave possible signatures.
And consider Boyajian’s Star (KIC 8462852), whose odd light curves drew it to the attention of citizen scientists at the Planet Hunters project and subsequent worldwide scrutiny. Numerous natural phenomena have been put forward to explain what we are seeing here, but light curves like this could also be the sign of an extraterrestrial civilization working on some kind of massive project (a Dyson sphere inevitably comes to mind, but who knows?)
It made sense, then, to make Boyajian’s Star a SETI target, which is why the SETI Institute used the Allen Telescope Array to search for radio emissions, a two-week survey that produced no evidence of artificial radio signals coming from the system. For more on this investigation, see Jim and Dominic Benford’s Quantifying KIC 8462852 Power Beaming, which analyzed the ATA results at radio wavelengths. But note the following, which summarizes what the Benfords believe would be detectable given the instruments used in the attempt. As you can see, not all detectable signals would come from power beamed, for example, to an interstellar mission. Some of them definitely include applications within the target system:
- Orbit raising missions, which require lower power, are not detectable at the thresholds of the Allen Array.
- Launch from a planetary surface into orbits would be bright enough to be seen by the 100 kHz observations. However, the narrow bandwidth 1 Hz survey would not see them.
- Interplanetary transfers by beam-driven sails should be detectable in their observations, but are not seen. This is for both the narrow 1 Hz and for the “wideband” 100 kHz observations.
- Starships launched by power beams with beamwidths that we happen to fall within would be detectable, but are not seen.
Image: Power beaming to drive an interstellar lightsail. Credit: Adrian Mann.
But let’s move back into the optical. Nate Tellis (UC-Berkeley) recently worked with astronomer Geoff Marcy to analyze Keck data archives on 5,600 stars observed between 2004 and 2016, using a computer algorithm fine-tuned to detect laser light (see A Search for Laser Emission with Megawatt Thresholds from 5600 FGKM Stars,” preprint here). The search was an excellent way to put thousands of hours of accumulated astronomical data to work — who knows what discoveries may lurk within such datasets? As a part of the effort, the astronomers studied Boyajian’s Star, again finding no detectable signals. Potential candidates that did emerge in the survey all turned out to be the result of natural processes.
But power beaming is a possible observable as any local civilization goes about moving things around in its own system. Leakage from a beamed power infrastructure is something we’ve focused on here frequently (see, for example, Power Beaming Parameters & SETI re KIC 8462852). Power beaming could be what enables a space-based infrastructure, one that would be capable of large-scale engineering and also of producing the kind of power beams that could drive spacecraft at high velocity to other stars.
But we needn’t exclude communications entirely. Jim Benford has pointed out that any civilization using large-scale power beaming would be aware that its activities could be visible to others. If it had the desire to communicate on such a random basis, the ETI civilization could embed a message within the beam. A kind of interstellar message in a bottle, thrown into the cosmic sea with each sweeping power beam that does local work.
All of this should reinforce the key issue that the Laser SETI project addresses — such beams, working within their own planetary system, would appear in our sky as transients. We return to the core issue, the need for an all-sky survey that observes continuously. Making no assumptions about any desire to communicate, such a survey nonetheless is capable of spotting the signs of a working civilization going about its business. It should, I would wager, also pick out new astrophysical phenomena that will add to our knowledge of the galaxy.
