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SETI: Rummaging in the Data

Astronomy is moving at a clip that sees more data accumulated than can possibly be examined at the time they’re collected. We’re creating vast storehouses of information that can be approached from various angles of study. Now ponder how we might use these data for purposes beyond what they were collected for. In a new paper submitted to the Astronomical Journal, Ermanno Borra (Université Laval, Québec) looks at how standard astronomical spectra — including those already taken — can be used as part of SETI, the Search for Extraterrestrial Intelligence.

Here’s the idea: Suppose somewhere out there a civilization decides to reveal its existence to the rest of the galaxy. These extraterrestrials reason from their own experience of science that an advanced civilization will study the sky and take spectra of astronomical objects. These spectra become the medium upon which the senders impose their signal. At our end, spectroscopic surveys of vast numbers of stars allow us to accumulate data that may contain evidence of an unusual signal, a spectrum deliberately crafted to be so striking that it calls attention to itself.

How to create the signal? Through modulating the spectrum by sending short bursts of laser light, an idea Borra addressed in a 2010 paper, as discussed again in this one:

Borra (2010) shows that periodic time variations of the intensity signal originating from a pulsating source modulate its frequency spectrum with periodic structures. Periodic time variations of the intensity signal originating from a pulsating source with periods between 10-10 and 10-15 seconds would modulate its spectrum with periodic structures detectable in standard astronomical spectra. Periods shorter than 10-10 seconds could be detected in high-resolution spectra. Note that the modulation is rigorously periodic in the frequency units spectrum but not in the wavelength units spectrum.

Image: A panoramic image of the Milky Way. Could we use spectroscopic data from surveys already conducted to find evidence of other civilizations? Credit: Photopic Sky Survey.

You can see the beauty of this proposition. We already have mountains of spectroscopic data acquired for other studies, data that can be analyzed visually or through Fourier transform software. Borra wants to make astronomers aware of this potential use for such data as a complement to existing optical SETI work carried out at sites like the Wyeth Telescope (Harvard/Smithsonian Oak Ridge Observatory) and the SERENDIP instrument at UC-Berkeley. The latter are cutting-edge projects, but with some limitations, the biggest being that they can observe only one object at a time. They also require either dedicated instruments or telescope time on standard telescopes, a limitation that a database hunt of earlier work surmounts.

Borra finds that the energy needed to generate the needed signals is feasible even for a civilization like ours — he analyzes it in terms of current equipment by referencing diode-pumped laser technology similar to the Helios laser designed at Lawrence Livermore National Laboratory for inertial confinement fusion studies. The result: An isolated signal transmitted at 1000 light years (a sphere within which there are roughly a million stars) would be detectable with today’s instruments. A spectroscopic survey like the Sloan Digital Sky Survey could find it.

By ‘isolated’ signal, Borra means a signal sent from a place distant enough from the home star so that the signal would not be directly superimposed on the spectrum of the star itself. The other case is a signal sent from the home planet, one that would therefore mix with the stellar spectrum. Now the signal becomes harder to detect because it is considerably weaker than the total energy of the stellar spectrum, requiring the extraterrestrial senders to resort to more powerful sources. Here Borra references the 2004 paper from which he drew the Helios comparisons:

… we can assume that, considering the Moore’s law of laser technology, a more advanced civilization should have no trouble increasing the laser power by 2 to 3 orders magnitude making the signal readily detectable. For a solar-type star at 1000 ly the signal would then be comparable to the stellar background and thus easily detectable… The Moore law suggestion is intuitively justified by simply imagining how Howard et al. (2004) and the present article would have been received before the invention of the laser 60 years ago, when the signal would have had to be generated with light bulbs!

A Kardashev Type I civilization should be able to manage the power output to make its superimposed signal observable at nearby stars, but a Type II would be capable of harnessing all the energies available from its home star, making the production of such signals feasible for vast numbers of potential recipients. Because, as Jill Tarter has often commented, civilizations trying to contact us are likely to be more advanced technologically than we are, the possibility of finding such Type II civilization signals in astronomical spectra becomes an intriguing issue.

What’s appealing about Borra’s approach is its sheer simplicity. The database-mining idea for SETI has a history in the literature going back to papers in 1977 (Zbigniew Paprotny) and 1980 (Daniel Whitmire and David Wright), who suggested searching for anomalous spectral lines originating from radioactive fissile waste material. Geoff Marcy and Amy Reines have carried out a search of 577 nearby stars looking for emission lines too narrow to be natural. Signal-finding algorithms incorporated into existing software can be used with present and future spectroscopic data to continue this hunt, all achieved, as Borra says, with a few lines of code.

Is a SETI signal to be found in our databases? The paper is Borra, “Searching for extraterrestrial intelligence signals in astronomical spectra, including existing data,” accepted for publication by the Astronomical Journal (preprint). Thanks to Antonio Tavani for first calling this one to my attention, and several other readers who also sent in the link.


Comments on this entry are closed.

  • ljk November 8, 2012, 11:57

    I guess we better find ways to ramp up our SETI/METI and interstellar craft efforts, otherwise we will just keep debating this for at least the rest of our lives. I am not counting on an alien ship showing up any time soon, either, at least the kind that want to make themselves known to us. Oh, but I will probably be told in detail how I got that wrong, too. Darn that American-bred individualism of mine.

  • ljk November 8, 2012, 16:27

    I don’t know why this didn’t solidify in my mind sooner: Eniac, you wonder why ETI haven’t obviously been to Earth before if at least one of them is intent on colonizing the galaxy.

    Well, that whole “Don’t be stepping on no native microbes” thing could be one answer. We have evidence that life on Earth started not long after the place cooled down. Assuming it wasn’t transplanted by visitors in the first place, would it be impossible to assume that ETI might leave alone any worlds with life on them, even little ones with barely enough brains to eat and reproduce?

    With 400 billion star systems composing the Milky Way, there may be plenty of other more viable places to go for a colonizing species than Earth, which has had life on it for over 3 billion years and maybe more. That may be the hallmark of a highly intelligent species, one that does deliberately try to harm or exterminate creatures lower than itself.

  • Eniac November 8, 2012, 23:35


    With 400 billion star systems composing the Milky Way, there may be plenty of other more viable places to go for a colonizing species than Earth, which has had life on it for over 3 billion years and maybe more.

    The 400 billion number is a red herring. If you are a society with a history of colonization, having fully developed your system, you face the following two possibilities:

    1) You are in the interior of the domain of your species (true for most except at the very beginning)
    2) You are near the frontier of an ongoing expansion (only possible while the galaxy is not yet filled)

    In the first case, there are no options for colonization, because all the neighboring systems are either occupied, or off limits (if there is such a thing).

    In the second case there is a limited number of systems available at most a few hundred, depending on the maximum distance you are willing to travel.

    In no case does it matter how many stars there are in the galaxy. Not even one little bit.

    That may be the hallmark of a highly intelligent species, one that does [not] deliberately try to harm or exterminate creatures lower than itself.

    This is a valid possibility. But the sentiment has to be so thoroughly ingrained in the very nature of the species that out of the 10-100 (again, depending on the maximum travel distance) civilizations that surround the off-limits star, none will break the taboo, not even once in a billion years.

    We do not see this amount of resolve in human civilizations. I find it hard to even begin to imagine it.

  • ljk November 9, 2012, 10:55

    Eniac, how does this limiting colonization scenario compare with your other comments about how one species will eventually colonize the entire galaxy? And by “entire” I presume you mean ALL of the Milky Way or something pretty darn close to it.

    So if ETI colonizers do not tread on systems that are occupied, either by an intelligent and civilized species or a collection of algae floating in a pond, would this not be a possible reason why Earth has been left alone, at least when it comes to colonization? Humanity’s existence on the cosmic scale is certainly short, but as I said elsewhere, we have had life on this planet for over 3 billion years and probably since Earth cooled down after forming.

    As for your comment about no ETI ever breaking the so-called taboo of interfering with other life forms on alien worlds and how unlikely that seems given human behavior past and present: If that is the case, then why dismiss my idea that if humans cannot keep a galactic colonization effort going, wouldn’t other intelligences who I presume are not immortal godlike beings and therefore virtually infallible also have trouble maintaining far-flung civilizations over the eons?

    Not that I ever thought being alien = better and more perfect than humanity, but I am thinking more and more that extraterrestrial life, including the intelligent kind, shares more in common with us than perhaps often thought. This would naturally include the ability to completely drop the ball even on major important plans to ensure their survival.

    How ironic if that was a bigger reason for their lack of presence than the vastness of the Universe in both space and time and our relative cosmic obscurity. And of course keeping in the possibility that alien minds and bodies will behave in very alien ways.

    Humans who want to seriously explore the stars and communicate with ETI are still the minority on this planet. So may it be the same with alien cultures, especially those that are emerging on the cosmic scene as we are.

  • Eniac November 9, 2012, 22:30

    Eniac, how does this limiting colonization scenario compare with your other comments about how one species will eventually colonize the entire galaxy?

    There is nothing limiting about my scenario. A species’ habitat will expand steadily under this scenario, until the galaxy is filled, less than a billion years later. I am not sure what it is you do not understand here.

    If that is the case, then why dismiss my idea that if humans cannot keep a galactic colonization effort going, wouldn’t other intelligences who I presume are not immortal godlike beings and therefore virtually infallible also have trouble maintaining far-flung civilizations over the eons?

    Here is this same fallacy again, which I seem to be unable to get across to you. You need nothing far-flung to spread a species across the galaxy. No interstellar coordination at all. All it takes is one inhabited system with the ability to colonize neighboring systems. Soon, there will be two inhabited systems, then four, then eight, etc.

    In the later growth phase, there will be an expanding spherical frontier, which will eventually reach the farthest corners of the galaxy, which is when colonization will stop. Civilizations need not be far-flung nor durable, as long as the species does not go extinct. Civilizations will be limited to single star systems as a rule, and if they decline and fall, they will be superseded by others soon enough, all within the same species.

    This would naturally include the ability to completely drop the ball even on major important plans to ensure their survival.

    With a species spread over many star systems, there simply is no ball that can be dropped to eliminate all of them. If you disagree, please describe a scenario that leads to the simultaneous extinction of hundreds of independent civilizations spread over hundreds of stars (which would be the case near the very beginning of the expansion, after about 10 generations of colonization)

    Your fallacy seems to be the idea that some sort of concerted effort is needed to “maintain” a species’ spread across the galaxy. Nothing could be further from the truth. The process is akin to a forest fire or bacteria growing in a dish. Easy to start, hard to stop.

  • Eniac November 9, 2012, 23:35

    Let me try to make my scenario as short and clear as I can:

    Colonization will always be local, involving only neighboring stars (two, in fact, the source and the target). The choice of target will mostly be limited to relatively few stars closest to the source. The decisions are made in the source system alone. Resources, too, will be mustered by the source system alone, in similar fashion to (and aided by historic knowledge of) the original first colonization from the one and only motherworld.

    The consequence of repeated application of this local process is an inexorable global expansion leading to a galaxy that is completely inhabited, in less than a billion years.

    Let me know if I can do anything else to explain this better.

  • ljk November 12, 2012, 11:53

    No, I get it. I just find the idea of interstellar colonies surviving for millions of years intact a bit optimistic, but then again I thought that human civilization would be brought low by nuclear war decades ago, so it is good to be wrong here, right?

    Let’s face it, we have a data point of one intelligent technological species that was largely agricultural just a few centuries ago and, to paraphrase Douglas Adams, really did think that digital watches were neat things mere decades in the past. Throw in the fact that alien beings evolving on alien worlds could possess traits and go certain ways in their development that widely differ from ours and who knows what might take place in the Milky Way over its ten billion year existence?

    So the next questions are:

    When could this one billion year colonization effort have taken place? If it happened early in galactic history, would it keep recycling or just need to occur once? Would we be able to find artifacts or remains from their efforts from several billion years ago? Other than fossils, what artificial materials can last for that long when stuck on a geologically active planet, as I am assuming one would need a “lively” world to live upon.

    Or maybe the galactic colonization “wave” has just been underway for a few million to say half a billion years and they have yet to reach the Sol system. Or their initial scout probes are here and they find it quite easy to hide from us. Or maybe they are living in the Kuiper Belt or Oort Cloud, also very easy to conceal from humanity. Or they are just avoiding a system with life as we have already discussed.

    As it took billions of years to go from single-celled organisms to talking, walking primates with car keys on this planet at least, could this be the case for biological evolution on most other worlds? Again, I am trying to avoid the wilder possibilities for alien life for the sake of rational discourse at the moment. Just throwing out the idea that while we may or may not be the first intelligent species in the galaxy, there may be others ahead of us but still not so far advanced that they’ve been able to cover the Milky Way by now.

    One of the parameters of the Kardashev scale of ETI development is that Type 3 is supposed to utilize the resources of an entire galaxy of stars. This has been interpreted as a civilization (or civilizations) visibly utilizing virtually every star in a galaxy. Now if such a thing is going on the Milky Way, it is not terribly obvious to us, but then again would we really know what to look for and how many, professionals especially, would agree with “intelligent design” as an answer? If an advanced ETI were, say, mining various solar systems, would we be able to see this? I am pretty safe in saying that said species would likely not be advertising this activity to the rest of the celestial neighborhood.

    Or maybe they just make their own universes which they can control and set to their liking and say Adios to our Universe.

    Or, just as many seem very willing to accept the possibility that no other smart beings exist in the galaxy beyond Earth, you might have to at least entertain the concept that no one has come along who has had the awareness, desire, or will to attempt colonizing the entire Milky Way. Life itself seems to be an aberration among all the elements we can see in the wide-scale view of the Universe; certainly life is a very tiny thing physically compared to say a galaxy or even a typical Main Sequence star.

    Until oh so recently, a person who advocated mere flight, let alone galactic colonization, was a definite aberration among its fellow humans. Perhaps this is yet something else shared by other intelligences: They are too busy fighting and entertaining themselves to support or care about the ones who want to know what is out there beyond their little rock in space.

  • ljk November 12, 2012, 12:11

    Eniac, thinking more on the subject, where did you get the number of 1 billion years for galactic colonization?

    Ian Crawford estimated in a Scientific American article from 2000 that a dedicated humanity could colonize the galaxy in a mere 3 million years. Later on he changed his estimates to anywhere from 5 to 50 million years, which is still pretty darn fast on a cosmic time scale.

    I cannot seem to find Crawford’s 2000 SA paper online, but he does have a pretty cool list of relevant articles from his bibliographic Web page here:


    Just to keep things interesting, did you see this piece from 2009:


  • ljk November 30, 2012, 10:37


    A new class of SETI beacons that contain information (22-aug-2010)

    Authors: G. R. Harp, R. F. Ackermann, Samantha K. Blair, J. Arbunich, P. R. Backus, J. C. Tarter, the ATA Team

    (Submitted on 27 Nov 2012)

    Abstract: In the cm-wavelength range, an extraterrestrial electromagnetic narrow band (sine wave) beacon is an excellent choice to get alien attention across interstellar distances because 1) it is not strongly affected by interstellar / interplanetary dispersion or scattering, and 2) searching for narrowband signals is computationally efficient (scales as Ns log(Ns) where Ns = number of voltage samples).

    Here we consider a special case wideband signal where two or more delayed copies of the same signal are transmitted over the same frequency and bandwidth, with the result that ISM dispersion and scattering cancel out during the detection stage. Such a signal is both a good beacon (easy to find) and carries arbitrarily large information rate (limited only by the atmospheric transparency to about 10 GHz).

    The discovery process uses an autocorrelation algorithm, and we outline a compute scheme where the beacon discovery search can be accomplished with only 2x the processing of a conventional sine wave search, and discuss signal to background response for sighting the beacon.

    Once the beacon is discovered, the focus turns to information extraction. Information extraction requires similar processing as for generic wideband signal searches, but since we have already identified the beacon, the efficiency of information extraction is negligible.

    Comments: 33 pages, 8 figures, 1 table

    Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Other Computer Science (cs.OH)

    Cite as: arXiv:1211.6470 [astro-ph.IM]
    (or arXiv:1211.6470v1 [astro-ph.IM] for this version)

    Submission history

    From: Gerald Harp Ph.D. [view email]

    [v1] Tue, 27 Nov 2012 22:44:02 GMT (1926kb)


  • ljk December 5, 2012, 9:33

    5 December 2012

    ** Contacts are listed below. **


    In the search for rogue nukes, researchers have discovered an unlikely tool: astronomical radio telescopes.

    Ohio State University researchers previously demonstrated another unlikely tool, when they showed that South Korean GPS stations detected telltale atmospheric disturbances from North Korea’s 2009 nuclear test.

    Both techniques were born out of the discovery that underground nuclear explosions leave their mark — on the outer reaches of Earth’s atmosphere.

    Now, working with astronomers at the U.S. Naval Research Laboratory (NRL), they have analyzed historical data from the Very Large Array (VLA), a constellation of 27 radio telescopes near Socorro, New Mexico — and discovered that the VLA recorded a very similar pattern of disturbances during the last two American underground nuclear tests, which took place in Nevada in 1992.

    Dorota Grejner-Brzezinska, professor of geodetic and geoinformation engineering at Ohio State, said that the new findings help support the notion that GPS systems — and their technological successors, global navigation satellite systems (GNSS) — are viable tools for detecting clandestine nuclear tests around the globe. She added that now is a good time to begin developing the concept.

    “With a global availability of permanently tracking GPS networks now extending to GNSS, tremendous amounts of information are becoming available, and the infrastructure is growing,” she said. “We have a great opportunity to develop these ideas, and make a tool that will aid the global community.”

    Grejner-Brzezinska presented the findings in a press conference at the American Geophysical Union (AGU) meeting on Dec. 4 with study co-authors Jihye Park, a postdoctoral researcher in geodetic and geoinformation engineering at Ohio State, and Joseph Helmboldt, a radio astronomer at NRL. Park presented the research in a lecture at AGU on Dec. 3.

    While radio telescopes don’t cover the entire globe as GPS systems do, Helmboldt said that the two technologies complement each other, with telescopes offering higher-resolution measurements over a smaller area.

    “The observations we make as radio astronomers are not so different from GPS,” he said. “We may be looking up at a distant galaxy instead of down to the Earth, but either way, we’re all looking at radio waves traveling through the ionosphere.”

    The ionosphere is the outermost layer of the atmosphere, which begins approximately 50 miles above the Earth’s surface. It contains charged particles that can interfere with radio waves and cause measurement errors in GPS and radio telescopes.

    For that reason, both radio astronomers and geodetic scientists routinely monitor the ionosphere in order to detect these errors and compensate for them.

    “We’re talking about taking the error patterns — basically, the stuff we usually try to get rid of — and making something useful out of it,” Grejner-Brzezinska said.

    Park, who developed this analysis method to earn her doctoral degree at Ohio State, cited key similarities and differences between the GPS data from the 2009 North Korean nuclear test and the VLA data from the 1992 American tests: one on Sept. 18 named Hunters Trophy, and the other on Sept. 23 named Divider.

    The North Korean bomb is believed to have had a yield of about five kilotons. According to the GPS data, the wave front of atmospheric disturbance spread outward from the test site in the village of P’unggye at approximately 540 miles per hour. It reached 11 GPS stations in South Korea, China, Japan, and Russia in that first hour. In contrast, Hunters Trophy and Divider each had yields of 20 kilotons. Each blast created a wave front that quickly covered the 700 miles from the Nevada Test Site to the VLA, with a top speed of approximately 1,500 miles per hour.

    “Clearly, the U.S. explosions were much bigger than the North Korean explosion,” Park said. “The wave fronts traveled faster, and the amplitudes were higher. There are still details missing from the North Korean test, but we can learn a lot by comparing the two events.”

    Park will continue this work while she takes a new position at the University of Nottingham starting in January. She’s already found that GPS stations in the North Pacific recorded ionospheric disturbances during the deadly Japanese earthquake of 2011, and she will focus on how to differentiate between earthquake signals and nuclear test signals.

    Collaborators on this work include Ralph R. von Frese, professor in the School of Earth Sciences at Ohio State; Yu “Jade” Morton, professor in electrical engineering at Miami University in Oxford, Ohio; and Thomas Wilson, an astronomer at NRL.

    PIO Contact:

    Pam Frost Gorder
    +1 (614) 292-9475

    Science Contacts:

    Dorota Grejner-Brzezinska

    Jihye Park

    Joseph Helmboldt
    +1 (202) 404-6340

    Editor’s note: Both Grejner-Brzezinska and Park are best reached by email; contact Pam Frost Gorder to reach any of the sources during the meeting or to request an image of a wave front recorded by the VLA.