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Breakthrough Discuss: SETI in the Optical

At the Yuri’s Night party on Yuri Milner’s Palo Alto estate, I found myself thinking about a novel, Allen Steele’s Arkwright. Like Breakthrough Starshot, initial work on the starship in the book is funded by a wealthy man who wants to see a human future among the stars. The propulsion method is a beam-driven sail, though at that point the comparisons get strained, for Steele is assuming a much larger craft and a mission of colonization rather than a flyby. Even so, there was enough similarity to make a book I had been reading on the airplane seem prescient.

The music on Yuri’s Night was loud, the gathering crowd relaxed, and I had imagined it would be an entirely social event, but after a time we were called in to watch a short video about Starshot and then participated in a question-and-answer session with some of the project’s principal players, including Milner himself. It was a good chance to hear some of the challenges the project faces examined, and tomorrow we’ll look at many of these. We also have to dig back into the gravitational focus mission and its role in all this.

But I kept thinking about Steele’s target planet, around Gliese 667C, and pondering interstellar distances. Alpha Centauri is 40,000,000,000,000 kilometers out, a whopping 271,000 AU. I seemed to be feeling the distance as an almost tangible thing, suddenly realizing that I was completely frazzled from the day’s sessions. I’m compulsive about note-taking (I would wind up with 52 single-spaced pages on my MacBook), and that feeling of distance fatigue was actually a very physical weariness. I made an early night of it (and thank you, Jill
Tarter and Jack Welch, for your kind offer of a ride back to the hotel). I slept that night like I haven’t slept in years.


Time to Target

That morning, in the opening session on optical SETI, I had been wondering whether key papers, like the Cocconi and Morrison paper that launched serious SETI study in 1959, or the Townes and Schwartz paper that brought optical SETI to our attention, had begun a gradual cultural widening of our horizons. If many people I talk to in everyday life still don’t have a grasp of just how far away even the nearest stars are, it’s still true that SETI has brought the topic of other civilizations to the fore, as reflected in countless science fiction novels and films.

And now that we’re thinking about an actual interstellar mission, it falls to us, as Jill Tarter had reminded the conference that morning, to think about the SETI consequences of pushing sails between planets and stars. Let me quote her on the point:

“A fiducial for optical seti has been a petawatt transmitter focused by a ten meter telescope. And even though we don’t have signs of that kind of technology in our future for interstellar communications, Breakthrough Starshot demonstrates there is reason to believe there may be transient sources of emission as byproducts of other plausible activities.”

Plausible activities include, as we have seen yesterday, a beaming infrastructure within a stellar system that could drive spacecraft on missions of exploration and supply. But we don’t even have to assume that another species is necessarily exploring the cosmos. For surely, like us, they would be aware of the danger of rogue asteroids or comets within their own system, and possibly using beamed lasers to deflect their trajectories. The lesson: If we can imagine it, so can someone else. And if they were to build it, we just may be able to see it.

Eliot Gillum’s talk on optical SETI reinforced these ideas. The director of optical SETI at the SETI Institute, Gillum noted that the older search paradigm had been to look at small patches of the sky for just a few minutes. The assumption here is a continuous or rapidly repeating signal, but beamed power calls upon us to change strategies. ‘All sky all the time’ is Gillum’s solution, given our understanding that beaming presents huge problems of geometry. Are we lined up by chance to see a beam, and would we be able to recognize it when we did?

The beamed SETI observable is a bright transient, and we have more than a few of these in the catalog already, though we don’t know what they are. But Gillum pointed to a program called AllSat as an indication of how we might proceed. It’s a highly automated program whose prototype is now under construction, using multiple cameras to observe fields of view of 120 degrees. AllSat is about signal detection, not detailed characterization, but its six primary observatories would be a full-sky search allowing follow-up at higher apertures.


Image: Equipment for an all-sky optical SETI survey, as shown on one of Eliot Gillum’s slides.

Fast, sporadic, bright targets we would miss with older optical SETI methods should become observable in a five-year survey of the entire sky. Harvard’s Paul Horowitz discussed new photon-counting detectors and showed a notional design of a telescope that could be built around them. Horowitz and team began searching for intense laser pulses in 1998, understanding that the beam produced by a high-intensity pulsed laser teamed with a moderate-sized telescope — something that could be built with current technology — would appear during its pulse a thousand times brighter than the Sun.

But it was Philip Lubin (UC-Santa Barbara) who made the most explicit link between optical SETI and what Breakthrough Starshot is doing. Lubin told me during a break that the genesis of the current beamed sail concept as conceived by Starshot grew out of his recent “Roadmap to Interstellar Flight,” a lengthy paper submitted to the Journal of the British Interplanetary Society and available here. I should also mention in relation to SETI that a new paper, “The Search for Directed Intelligence” has just become available on the arXiv site.

The space for life to flourish in the universe is all but boundless, Lubin said, showing a one square degree image from the Hubble Ultra Deep Field and noting that 1018 planets could be in the view.

“We can stare at one square area of the sky and be looking at trillions of planets all the way out to a modest redshift,” Lubin said. “As to detection probability, consider that we are about to enable a class 4 civilization with Starshot. The beam — a phased array beam small enough to hit individual stars — would be detectable out to enormous distances with a modest telescope… Phased array telescopes grow out of technology like Starshot. We can take a picture, look along the line of sight, and know that vast numbers of planets are in that field of view.”

I should mention that Lubin’s civilization classification is not Kardashev’s; he’s drawing on a scale he discusses in his most recent paper, one in which Kardashev Level 1 is a Class 11. But whatever the classification, it’s clear that a beamed laser infrastructure raises questions about our own planet’s visibility, which invariably opens the METI (Messaging to Extraterrestrial Intelligence) debate. It was not a subject the conference spent a lot of time on, though it was clear from remarks I heard that opinion was sharply divided between those who found restrictions on METI pointless and those who called for consensus among a variety of disciplines before actively trying to raise the visibility level of our own civilization.


Image: Looking into the Hubble Ultra Deep Field. Credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI).

Extracting a SETI Signal from our Data

Amy Reines (NOAO) would follow Lubin with an analysis of narrowband SETI searching using radial velocity data. In radial velocity work, we are looking for the tiny Doppler shift an orbiting planet can produce in a star’s spectrum. A laser beam would need to outshine the star’s stellar photon noise, and Reines calculated that most lasers on Earth are already approaching a value that would allow such detections. This assumes a continuous laser beam rather than a pulse, the latter demanding higher power, and it must be directed at us to be detected.

Reines’ computer code could search spectra for possible laser emission lines, comparing a reference spectrum for each star to all other spectra of the star while eliminating random noise fluctuations. Most candidates for a laser turned out to be cosmic rays that hit the detector. One possible hit emerged, a spectral feature seen in three observations of the same star at the same wavelength, but the excitement was short-lived, as the ‘hit’ turned out to be an artifact in the CCD detector. But the methods can be applied to many optical SETI data mining studies.

We can also extend optical pulse SETI into the near-infrared, as Shelley Wright (UC-San Diego) explained, citing new near-infrared photomultiplier tubes (PMT) and avalanche photodiodes (APDs) — these exploit the photoelectric effect to convert light into electricity. We are moving, she said, to higher gain, lower noise and a larger dynamic range in the available instrumentation. The NIROSETI (Near-infrared Optical SETI) instrument built by Wright’s team at Lick Observatory exploits infrared’s advantages in the first near-infrared SETI experiment.

Of course, we might consider not sending or receiving optical or radio data, if Chris Rose is right. Arguing that we should ‘write, not radiate’ our data, Rose (Brown University) wrote a paper with Gregory Wright in 2004 that calculated the energy needed to communicate a given payload of bits. Maybe we should consider sending an artifact packed with information rather than an electromagnetic signal of any kind. If you’ve been reading Centauri Dreams for a long time, you’ll recognize the argument I wrote about in ET in a Grain of Sand.

Rose believes that it can be many orders of magnitude better (from the perspective of energy use) to write a message onto a medium and actually deliver it physically to the recipient, than to send it by radio or laser signal. Clearly he’s not talking about ongoing communications but archival purposes, such as a civilization wanting to send out a record of its great works (here the Voyager golden records come to mind). And he makes the case that for these latter purposes, a truck — or spacecraft — filled with storage media is a very reliable high bit-rate channel.

Of course, it has latency issues — it takes, on the interstellar scale, a long time to get where it’s going. It was a lively presentation punctuated by the question of how we might detect such ‘packages’ of data if they have already been sent to our system from another star. An even bigger question is what Rose described as ‘incursion or evolution.’ Are we ourselves the product of another civilization’s outreach, a ‘seeding’ of the cosmos in our stellar neighborhood? For that matter, should we consider seeding the universe ourselves as well as communicating?


Image: A panel discussion on SETI followed the talks. From left: Jill Tarter, Jim Benford, James Cordes (Cornell), Andrew Howard (University of Hawaii at Manoa), Andrew Siemion (UC-Berkeley), and Dan Werthimer (UC-Berkeley).

Tomorrow I want to draw on the Yuri’s Night panel on Breakthrough Starshot as well as Pete Worden’s talk on the second day of the conference. We need to run through some of the bigger Starshot challenges, and also discuss how the project might evolve over time. I had hoped to get into the gravitational lens dimension of this initiative, but rather than skimping on the presentation, I think I’ll target that for a concluding Breakthrough Discuss post on Monday.


Comments on this entry are closed.

  • Tom Mazanec April 21, 2016, 13:14

    One possible hit emerged, a spectral feature seen in three observations of the same star at the same wavelength, but the excitement was short-lived, as the ‘hit’ turned out to be an artifact in the CCD detector.

    Is it possible to ensure that such “artifacts” will not reoccur and waste our time trying to sort out?

    • Paul Gilster April 21, 2016, 14:15

      Artifacts like these are just what you get when you’re trying to sort out a new technology. I think they’re to be expected, and the key is to be able to identify them as the method is tuned up.

  • Giulio Prisco April 21, 2016, 13:17

    Re “The beam – a phased array beam small enough to hit individual stars – would be detectable out to enormous distances with a modest telescope.” (Lubin)

    Then if optical SETI finds nothing it will mean that one of the following is likely to be correct:

    1. There is nobody.
    2. Nobody wants to reach the stars.
    3. There are much better propulsion systems based on physics more advanced than ours.

    I don’t like 1 and find 2 difficult to believe. Therefore I hope that either optical SETI finds Starshot-like beams soon, or 3 is correct.

    • Michael April 22, 2016, 15:28

      Terrestrial torpor -Terrestrial lethargy-, can’t be bothered to get off their posteriors,

      ‘Nobody wants to reach the stars.’

      is more likely.

  • Coacervate April 21, 2016, 13:51

    Great reporting, thank you.

    My mind drifts to Buzz Aldrin’s “Encounter with Tibor” in which a plucky group of Centaurians make their way to Earth with some interesting adventures in time and space. I liked this book because it was a rare exception to most depictions of aliens as technical demigods. These guys were mortal and pushing the limits of their technology to get here.

    So I can’t help but wonder about things we could do to “meet them half way” so to speak. Such as provide a breaking beam to slow down a visitor’s relativistic approach.

    Of course they should send an announcement first…”Hey, can you see this light? We were wondering if you’d be able to provide a similar intensity breaking beam?”

    Dream on

    • Kamal Ali April 21, 2016, 23:29

      my thinking on this matter is that its far more likely that the two civilizations meeting are on very different points in their evolution, than they are technologically on a comparable level. If they are on a comparable level, then what you say is possible (as long as they are well aware of each other).

      • Coacervate April 22, 2016, 18:15

        I know you are right. Long odds, but I’m a risk talker.

        Our O2-rich atmosphere has been our “beacon” for a billion years. I wish we could find the wisdom, will and $ to at least look for their beacons.

        It is my guess that one outcome would be the end of war. Why? For the same reason we instantly calmed down whenever the teacher entered the room.


  • Tom Pliska April 21, 2016, 15:23

    I apologize in advance, but there’s a tangential question that has been bothering me for a while. Given a beam projector in space accelerating some distant sail, what do people think would be the best way to prevent the projector from accelerating in the opposite direction? Obviously you could cancel the thrust out by directing the beam intermittently in opposite directions, or at the same sail when the projector was at opposite sides of an orbit. Or, you know, rockets. But how have people discussed this problem in the past?

    • Andrew Palfreyman April 21, 2016, 16:45

      The reactive acceleration of the beamer reduces in proportion to its mass. So if it’s fairly massive, doing nothing will work for a while.

      For maintaining the beamer position more stably, it can simply be attached to a much more massive body, like an asteroid or a moon.

      In the event that neither of the above are convenient, the radiated power can be split into two diametrically opposite beams, with the inevitable halving of usable beam power.

    • Michael April 22, 2016, 15:34

      @Tom Pliska April 21, 2016 at 15:23

      ‘I apologize in advance, but there’s a tangential question that has been bothering me for a while. Given a beam projector in space accelerating some distant sail, what do people think would be the best way to prevent the projector from accelerating in the opposite direction?’

      Simple, if the beamer is in space let part of the beam go out the back to push a larger gravitational lens spacecraft out to the 550 AU point to arrive around the time the other crafts do at the target star cancelling the momentum, two birds with one stone.

    • Brett Bellmore April 23, 2016, 19:54

      Put the Beamer in orbit around a massive body, with the plane of the orbit perpendicular to the direction of the beam. The reaction force will just displace the orbital plane so that it is behind the central body. The Sun would serve the purpose.

      • Eniac April 25, 2016, 11:03

        Yup, that’s the best way.

      • Michael April 25, 2016, 21:10

        Would you not limit the region in which you can launch craft, the target may not be in that direction. I would have thought it better to use the counter force to do something useful.

  • Alex Tolley April 21, 2016, 16:05

    Maybe we should consider sending an artifact packed with information rather than an electromagnetic signal of any kind.

    Some ideas to elaborate on this theme with miniaturization.

    1. Assume extreme miniaturization. Coding at the atomic level. Literally grains of material could hold encyclopedias if suitably encoded.

    2. Assume vast numbers of data grains are dispersed for archival reasons. (c.f. This is an alternative approach to large “vessel” repositories as proposed by Rezabak).

    3. manufacture the grains so that they look obviously artificial – e.g. perfect cylinders at the atomic scale. Add a surface coating that makes them easily visible to em radiation.

    One advantage of such an approach is that such data grains need not be detected in a narrow time window as with radiation. These grains would be found in the stratigraphy of the rocks. Indeed the information from many civs could be found in different layers of the rocks.

    Unlike biology, there would be no changes in the DNA sequence, with evolution slowly corrupting the encoded messages.

    Ideally these grains should make themselves easily visible, by light, or by broadcasting simple messages when stimulated in some way.

    They have the advantage of allowing one-way communication without revealing the source position, unlike radiation methods.

    Brin’s Existence posited a similar approach, but with much larger objects and with active devices. I propose that these data grains are more akin to the Voyager golden record discs, data that would need to be read and decoded by the local technology.

    If the grains are able to transmit their contents when stimulated, this makes detecting and reading their contents much simpler.

    So perhaps we should be examining the rocks more carefully? We already look for tint mineral inclusions in rock samples. Perhaps amongst them are also data grains waiting to reveal the knowledge of past galactic civilizations now long gone.

    While Starshot is a high energy, targeted approach, I think that such data grains could be dispersed at 100’s km/s by the sun using atomically thin sails to capture the light or CMEs. They would be dispersed for as long as they were being produced. Maybe they could have crude targeting to ensure the majority ended up in star systems within a fraction of the galactic radius, maximizing the chances of them being found.
    A good place to look for these grains would be on geologically dead worlds, like our Moon, where they would accumulate on the surface, making them easier to detect.

    • Mike Fidler April 21, 2016, 18:55

      That makes alot of sense, but what about sending out genetic material in a virus that could alter or update the evolution of life on many planets. I could just see exterestial civilization’s spreading their DNA via virus’s to have dominace over the galaxy, maybe even wars or something like the Olympics. What would be the perfect package to send that material in?

      • Alex Tolley April 25, 2016, 13:29

        Replicating bacteria or viruses would solve the problem of numbers on arrival, but they would require the target world to be hospitable. A bacteria is a better choice as it would only require am environmentally friendly world, whilst a virus would need the help of the local life. Incompatibilities with the information storage and replicating method with local life might make this a non-viable solution.

    • Matt April 22, 2016, 0:48

      Of course the hard part about sending lots of data artifacts is putting them into a format that the recipients can identify and read. It is no good sending something that will not be recognized as data, or that cannot be deciphered if it is recognized.

    • Eniac April 24, 2016, 8:11

      There is no way that an object the size of a grain of sand could be located over interplanetary distance, much less interstellar distances. No matter what it is coated with.

      • Matt April 24, 2016, 11:37

        I think the way to locate a small object at a great distance is to make it radiant in some frequency.

        There might be some engineering work to do, like how to get the energy on and object that small. Also what are the best frequencies and how to point it.

        There is no need to look for grains of sand. This is a solved problem, at least at a conceptual level.

        • Eniac April 25, 2016, 0:24

          The “engineering problems” you speak of are all but insurmountable. This is not a solved problem, far from it.

          • Matt April 26, 2016, 16:52

            Eniac, please don’t give up before we start. Yes these are hard problems, that is the point, or part of it anyway.

        • Alex Tolley April 25, 2016, 13:24

          That is my thinking. The object would use local energy sources to transmit. This might be a heat gradient or an artificially created em source.

          • Eniac April 27, 2016, 16:02

            It seems you underestimate the immensity of distances in space and how they attenuate signals.

            The amount of power a device can store, channel, convert or reflect is limited by an amount related to the cube of its size. Even a ton-scale spacecraft (e.g. voyager) is completely undetectable across many AU, unless it’s high-gain antenna (meter scale) is radiating at full power (22W) and precisely directed at a very sensitive receiver. Everything less will drown in the noise. A grain of sand is many, many orders of magnitudes less visible. Both gain and power are greatly reduced with size, and a tight beam is fairly useless, anyway, for a beacon.

            Matt, I am not giving up, I am trying to redirect effort to solutions that actually have a chance to work.

      • Alex Tolley April 25, 2016, 13:26

        The objects would not be in interplanetary space, but settle on the surfaces of worlds/worldlets. They might be buried in the strata on geologically active worlds, or stay close to the surface on dead ones.

        • Eniac April 27, 2016, 16:10

          You’ll need a lot of them to settle on a planet (Really a lot, a very large lot) before there is even a tiny chance of one of them being found. Planets are big, grains small. And they’d be mixed with trillions and trillions of decoys in the form of real grains of sand.

  • Andrew Palfreyman April 21, 2016, 16:19

    Thank you, Paul, for the superlative reporting.

    It’s fascinating how a physics-educated billionaire, once stirred to action, can shake things up.

    One powerful idea, like this new StarChip concept, invites deep examination, and quickly leads from the very particular to the very general. By following the consequences of this one idea, a cascade of possible new developments emerges, all pulling us towards the future at an accelerated pace. It encourages us to send cheap swarms of spacechips to the stars, to build powerful laser beamers on the Moon and elsewhere, to implement a solar gravity telescope (gravscope), and more. There are slow, incremental approaches, and there are fast, Hail Mary style missions. Underlying all of this putative future development is the need to be able to launch a multiplicity of large pieces of hardware – laser beamers – at low cost. Low launch costs will turbo boost the space development timeline.

    We are encouraged to envision weaving a web of beamer light across and around our solar system.

    This enables cheap and rapid transport, for both acceleration from a source-side beamer and braking from a destination-side beamer. The web will grow incrementally outwards and beamers will increase in power and efficiency. It will be like laying down the tracks of an interplanetary railroad.

    On one-gee beams we can travel to the Moon, or back from it, in under 4 hours.

    Power beams can be used to remotely drill through the icy crusts of Europa and Enceladus to prepare for oceanic voyages of discovery.

    Eventually we’ll be able to quickly and cheaply install new gravscopes at will at any desired location, which in turn will accelerate exoplanet discovery and observation, which paves the way for viable and interesting interstellar targets. SETI sensitivity will receive a massive boost. To facilitate braking of outgoing payloads driven by our beamer web lying further in, we will need large steerable reflectors out in the Oort Cloud, tethered to massive asteroids to keep them in place. That is a much longer term prospect, but holds great potential.

    Cheap launches are the key to all this. Reusable rockets are a good start. Escape Dynamics might have provided yet another intermediate stepping stone with a solution enabled by power beaming technology, but could not attract sufficient funding. However, the real cost savings come when technologies like Skylon and StarTram get deployed. If they can be funded, that is. I see no signs of commanding vision here – yet.

    Indeed, can power beaming be funded by anyone but the military, intent on disguising a potent weapon as a steerable train track?

  • Mike Fidler April 21, 2016, 19:11

    The nice part about an all sky survey is that it should be able to see beacons that are not associated with individual stars. That would keep the sending civilization’s location unknown.

  • Sara April 21, 2016, 21:08

    Well, I’m guessing that no one has considered the possibility that Robert Heinlein suggested in the last few chapters of ‘Have Spacesuit – Will Travel’: that there are plenty of SETI others out in the Great Beyond, and they know about us, but they aren’t sure we’re mature enough to be contacted.

    We still pick terrible fights with each other. We spill stuff everywhere we go. We can’t pick up after ourselves. And we tend to smash other species that aren’t like us. So what is it that we could possibly offer another civilization if we can’t even behave ourselves at home?

    • Mike Fidler April 22, 2016, 9:34

      Ah, Juvenile delinquency, just hope we do not have to pay for it for the rest of our civilization’s history! Like in galactic prison…

    • David H. April 22, 2016, 12:59

      Yeah, that’s fine for popular fiction, but as a scientist, can you truly imagine a galaxy-scale dictatorship that actually succeeds at coordinating the actions of all these independent civilizations so that not even a *single individual* breaks their rules and contacts us?

      • Hiro April 22, 2016, 16:50

        I suspect that we might have been in a situation similar to the North Korea Sanctions, has anyone in this forum ever tried to contact any North Korean lately? There are many reasons for that to happen but I’ll give out a basic one, I blame it on the Flat-Earth Society which has several million members. ;)

        Well, there is another one that I know having high probability but it’s too early to cross into that domain. By the way, that Star-Chip project may have bird/insect control issue when flocks of bird or insects fly right above the those lasers.

    • Sara April 22, 2016, 16:39

      Yes, but David, what if there’s no ‘dictatorship’? What if it’s just an unwritten agreement? (Where you from? Earth. Earth? Eeeeeewww! C’mon kids!)

      On the other hand, what if there’s no other species like us anywhere we go? Plenty of life, but nothing even vaguely like us?

      That’s the whole point to speculation fiction.

  • Michael April 22, 2016, 2:03

    Neat orbit simulator, http://www.scottgalas.com/alphaCen/index.php of AC . If you put values above 3 AU you get really strange orbits.

  • Harry R Ray April 22, 2016, 9:35

    A continuous all-sky search IS greatly needed, but don’t forget its ANTITHESIS: A dedicated 24/7 search of TOP PROSPECTS, like KIC8462852, by a group of observatories spaced evenly around the globe to insure that AT LEAST ONE OBSERVATORY IS observing the target at all times. If Lubin is right, LOFAR, JVLA, and Green Bank will not find ANY signal from KIC8462852, even if ET’ actually DO exist there, because they will be using laser beaming instead.

  • David H. April 22, 2016, 12:50

    Sending data written in a physical medium might get great bandwidth (if not latency), but it requires the receiving party to have a pretty serious catcher’s mitt. “Reading” the Voyager disks might be easy, but if you etch something into a starchip sent out at .2c, nobody could possibly read it.

    • Michael April 26, 2016, 12:36

      The physical data could be transmitted via radio waves using the sail as the antenna at close approach.