≡ Menu

A SETI Search of 10 Million Star Systems

As it is considered a precursor installation, the Murchison Widefield Array (MWA) in Western Australia doesn’t get the press that its proposed successor, the Square Kilometer Array (SKA) regularly receives. That’s to be expected, given the scope of the SKA, which will involve telescopes in both Australia and South Africa. 14 member countries are developing a project that is to reach over a square kilometer of collecting area, containing thousands of dishes and up to a million low-frequency antennas. If it is built, SKA’s angular resolution and survey speed will allow surveys thousands of times faster than those now being conducted.

But the Murchison precursor is alive and well, working the 70–300 MHz range and mapping the radio sky. Established by a consortium of universities — MIT, Swinburne, Curtin and Australian National University — the telescope is located on a site selected by these universities and managed by Curtin University. CSIRO, Australia’s national science agency, would later take over management of the site, which also now houses their SKA precursor instrument, ASKAP.

The MWA may be 50 times less sensitive than the SKA, but it has been put to work in areas ranging from the heliosphere to neutral hydrogen emission from the early universe. Its remit also includes several SETI studies, the latest being a search in the area of the constellation Vela (originally part of the larger Argo Navis constellation). The International Centre for Radio Astronomy Research calls this latest survey “the deepest and broadest search at low frequencies for alien technologies.” The results are now in the books, as reported in Publications of the Astronomical Society of Australia.

CSIRO astronomers Chenoa Tremblay and Steven Tingay (Curtin University) used the telescope’s wide field of view to observe millions of stars simultaneously. No technosignatures were detected, leading Tingay to observe:

“As Douglas Adams noted in The Hitchhikers Guide to the Galaxy, ‘space is big, really big’. And even though this was a really big study, the amount of space we looked at was the equivalent of trying to find something in the Earth’s oceans but only searching a volume of water equivalent to a large backyard swimming pool. Since we can’t really assume how possible alien civilisations might utilise technology, we need to search in many different ways. Using radio telescopes, we can explore an eight-dimensional search space. Although there is a long way to go in the search for extraterrestrial intelligence, telescopes such as the MWA will continue to push the limits—we have to keep looking.”

The scientists observed the sky in Vela for 17 hours, and point to the capabilities of the coming SKA, which if completed could be available late in this decade. SKA would extend the SETI search into billions of star systems, and would be capable of detecting what Tingay calls “Earth-like radio signals” from relatively nearby planetary systems, meaning, I assume, leakage radiation as opposed to directed signals designed to be interstellar. The current work follows earlier MWA surveys, one toward galactic center, the other in the anti-center direction.

From the paper:

Overall, our MWA surveys show the rapid progress that can currently be made in SETI at radio frequencies, using wide field and sensitive facilities, but also show that SETI surveys have a long way to go. The continued use of the MWA, and the future similar use of the SKA at much higher sensitivities, offers a mechanism to make significant cuts into the haystack fraction of Wright et al. (2018), while maintaining a primary focus on astrophysical investigations, making excellent commensal use of these large-scale facilities.

Image: Dipole antennas of the Murchison Widefield Array (MWA) radio telescope in Western Australia. Credit: Dragonfly Media.

On the matter of ‘haystack fractions,’ the phrase comes from a 2018 paper from Jason Wright (Penn State) and co-authors (two students in a graduate SETI course taught by Wright), which attempts to calculate the total fraction of the ‘haystack’ that has been searched to date, producing a result not far off what Jill Tarter calculated back in 2010: “…our current search completeness is extremely low, akin to having searched something like a large hot tub or small swimming pool’s worth of water out of all of Earth’s oceans.“ Tarter’s comparison was to a drinking glass’s worth of seawater, so we’re in the same range.

Although I cited it in an earlier article (see Into the Cosmic Haystack) this quotation from the Wright et al. paper bears repeating:

We should be careful, however, not to let this result swing the pendulum of public perceptions of SETI too far the other way by suggesting that the SETI haystack is so large that we can never hope to find a needle. The whole haystack need only be searched if one needs to prove that there are zero needles—because technological life might spread through the Galaxy and/or technological species might arise independently in many places, we might expect there to be a great number of needles to be found. Also, our haystack definition included vast swaths of interstellar space where we have no particular reason to expect to find transmitters; humanity’s completeness to subsets of this haystack—for instance, for continuous, permanent transmissions from nearby stars—is many orders of magnitude higher.

Noting that “the dream of ‘all-sky, all the time” high bandwidth coverage is still worth pursuing, and singling out the Tingay et al surveys at the MWA in particular, Wright and colleagues say that surveys with large bandwidth, long exposures, repeat visits and good sensitivity allow for searches that are orders of magnitude faster than surveys without these qualities. Indeed, the three MWA low frequency surveys, because of their very wide field and sensitivity, dominate the haystack search volume, and as Wright notes, they did this in only a few hours of searching. The paper also notes how rapidly Breakthrough Listen is cutting into this search space, and that was before the most recent Breakthrough results were announced (see SETI: Going Deep with the Data Search).

Image: A 20-second exposure showing the Milky Way overhead the AAVS station. Credit: Michael Goh and ICRAR/Curtin.

The paper is Tremblay and Tingay, “A SETI Survey of the Vela Region using the Murchison Widefield Array: Orders of Magnitude Expansion in Search Space”, Publications of the Astronomical Society of Australia September 8th, 2020 (abstract). The Wright paper is “How Much SETI Has Been Done? Finding Needles in the n-Dimensional Cosmic Haystack,” Astronomical Journal Vol. 156, No. 6 (14 November 2018). Abstract / Preprint.

tzf_img_post
{ 28 comments… add one }
  • Eniac September 9, 2020, 17:20

    When I hear the haystack and glass of water analogies, I imagine myself at the beach trying to get that glass of water. I walk over mushy seaweeds and cut my feet on seashells before I get a chance to collect any water at all, and even from far away I already saw seagulls circling.

    The point being, you don’t have to search the ocean to see that there’s life. If you saw no life, for it to exist you’d have to assume that it’s stayed in some small and restricted space for all time. That is not the nature of life.

    • Alex Tolley September 9, 2020, 21:31

      The SETI folks cling to the idea that any ETI will most likely stay in their home system. Allowing them to have interstellar flight gets them in the weeds with UFOlogists which they desperately want to avoid. Their analogy would be a label full of sterile petri dishes with growth medium. But only a few have any organisms in their media. However long you wait, those organisms will not spread to other dishes.

      I think this is wrong, and our early tentative steps to spread life (accidentally) within the solar system and eventually to the stars suggests that unless there is some unforeseen filter ahead of us, humanity in some form will spread to the stars. As we know from simulations, the galaxy will fill up with life and intelligence in a cosmic eyeblink. If humans had starships when they emerged, 200-300,000 years ago, they would have colonized a chunk of the galaxy already. If it was the Hominid line that had starships, there wouldn’t be a star without a civilization occupying it.

      The GHAT project assumed that KIII civilizations exist and would alter the output of their home galaxy. Why should we imagine that our galaxy is any different? They have found nothing so far, matching our success in our own neighborhood. It gets us back to the Fermi Question – why are they not obvious? Any answer has to apply to ALL emerging civilizations. Like deities, one cannot prove they don’t exist, but the simplest answer is because they don’t.

      Hope springs eternal, and we can afford to spend some resources looking for ETI. My focus would be on SETL, because complex life is confined to its home system, with very few organisms able to make the journey between the stars unassisted by technology. The likelihood of success is higher and any discoveries will potentially stimulate technology to reach that life to study it, and perhaps monetize it.

      • Michael Fidler September 11, 2020, 1:47

        Interesting, but new paper says M4-M10 may be the most habitable and they have the long term erosion XUV stellar flares levels to keep the atmosphere habitual! Sounds crazy but read the 4. CONCLUSION AND DISCUSSION.

        Stellar Flares versus Luminosity: XUV-induced Atmospheric Escape and Planetary Habitability.

        “Space weather plays an important role in the evolution of planetary atmospheres. Observations have shown that stellar flares emit energy in a wide energy range (10^30-10^38 ergs), a fraction of which lies in X-rays and extreme ultraviolet (XUV). These flares heat the upper atmosphere of a planet, leading to increased escape rates, and can result in atmospheric erosion over a period of time. Observations also suggest that primordial terrestrial planets can accrete voluminous H/He envelopes. Stellar radiation can erode these protoatmospheres over time, and the extent of this erosion has implications for the planet’s habitability. We use the energy-limited equation to calculate hydrodynamic escape rates from these protoatmospheres irradiated by XUV stellar flares and luminosity. We use the Flare-Frequency Distribution of 492 FGKM stars observed with TESS to estimate atmospheric loss in Habitable Zone planets. We find that for most stars, luminosity-induced escape is the main loss mechanism, with a minor contribution from flares. However, flares dominate the loss mechanism of ∼20\% M4-M10 stars. M0-M4 stars are most likely to completely erode both their proto- and secondary atmospheres, and M4-M10 are least likely to erode secondary atmospheres. We discuss the implications of these results on planetary habitability.”

        Part of the CONCLUSION AND DISCUSSION.

        “M0-M4 stars are the most likely ones to erode secondary atmospheres, as seen in Figure 5, because they are able to maintain
        relatively high XUV irradiation levels over long timescales. A combination of high XUV from stellar luminosity and flares and small star-planet distance makes these planets especially sensitive to erosion of both proto- and secondary atmospheres. On the other hand, the least likely ones to erode their secondary atmospheres are M4-M10 stars, which consisted of the most stars whose primary loss mechanism was flare-induced. These results have significant implications for planetary habitability because about 75% of stars in the Milky Way are M-dwarfs (Owen & Mohanty 2016) and observations suggest that they host twice the number of planets around them compared to other stars (Hardegree-Ullman et al. 2019).”

        The only other problems are protons but a strong magnetic field around the planet may control it.

        • Michael Fidler September 11, 2020, 9:36

          Always forget to put the paper when I get excited:

          Stellar Flares versus Luminosity: XUV-induced Atmospheric Escape and Planetary Habitability.
          https://arxiv.org/abs/2009.04310

    • AlexTru September 10, 2020, 3:35

      Good point, perfect arguments.
      Reality is – SETI’s philosophy in stagnation.
      In distinguish to real life , needle in the stake does not reproduce it self and do not consume surrounding materials for “needle” copy reproduction, but life does that…

  • Geoffrey Hillend September 9, 2020, 18:21

    Even the Square Kilometer Array will not be nearly large enough to detect the leakage of radio and TV signals from a nearby exoplanet due to the inverse square law. The leakage will be too weak to detect. It would have to be a directed signal with a lot of power.

  • James Benford September 9, 2020, 20:00

    SETI, is testable and falsifiable only to a certain degree. And nobody goes fishing with a waterglass! They use a net.
    And the ‘SETA is like searching for a Needle in a haystack’ analogy is a defeatist one. As commonly used, it’s a metaphor for an effort that’s a certain failure.

  • Ron S. September 9, 2020, 21:24

    I just skimmed the paper and I have to say that it left me cold. I don’t see the value. If the purpose is to secure SETI funding it may the opposite of the intended effect since the search space is so vast that any feasible search would only dip into the “ocean” a few times rather than once so that the probability of success remains indistinguishable from zero.

    On a more technical note, one important flaw of the haystack analysis is that it treats all points in the multi-dimensional haystack as having equal probability. That is, a constant pdf. Let me demonstrate by roughly segmenting signal categories.

    I’ll call the first category Sagan signals. These are directed communications initiated by their reception of our EM leakage. This is roughly 40 ly radius (based on 1940 war radar, although the specific example isn’t critical). If they can detect that leakage they can easily transmit a directed signal of high SNR (signal to noise ratio), and indeed multiple signals of high received strength. We would find it difficult to miss. Sagan understood this well and used it in “Contact”.

    The second is beacons, which the paper spends some time discussing. These are almost certainly non-directional or possibly periodic with low duty cycle by electronically targeting a large quantity of stars. They are non-directional since they cannot be certain when and where to aim (see first category). The energy budget is enormous, and I mean really really big. Targeting stars/planets with bio-signatures helps little since, even in Earth’s case, the existence of a receiver on a life bearing planet is during a tiny fraction of the time span of the bio-signature. It’s extremely expensive to run a beacon and the potential payoff is near zero.

    The third category is leakage detection. For a variety of technical reasons our ability to succeed is extremely poor (for example, what Geoffrey describes). That is, the probability is close to zero (a dip in the ocean of the n-dimensional haystack). In consequence the motivation for funding the search is poor. Once there was some societal motivation, but only until the scale of the challenge was better understood. Again, the payoff is near zero.

    I have nothing against SETI and I really do like the concept but let’s not deceive ourselves. As the cliche says: hope is not a strategy.

  • Robert Flores September 10, 2020, 0:47

    If nothing else, this will certainly weaken the argument for
    advanced life evolving on Red Dwarves, over the project time, This sample run probably eliminated around 6,000 Red Dwarfs, assuming we can pic up some transmission noise from 250LY.
    At 250 Ly the volume contains around 250,000 stars X ~ 80% (lose approx of percent of M class stars overall) X ~3% of Sky Surveyed in the Vela sky patch, = 6,000

  • Gary Wilson September 10, 2020, 16:58

    I think the problem is what we are looking for rather than the fact we are not finding ETI signals of an EM kind. SETI is one approach to looking for ETI and many are now coming to the conclusion it is highly unlikely it will be successful in any human time frame. How big is a human time frame? I have no idea since humans get bored and lose interest in a matter of seconds in many cases. So SETI won’t likely reveal any ET’s in years or even scores of years in all probability. But let people try. Personally I like the tried and true method of accumulating data of all kinds about star systems and exoplanets over as long a time frame as we can. It will eventually be our Encyclopedia Galactica. We’re going to find lots of life out there and we have no idea what it will look like, how “intelligent” it will be, what its’ motivations are and so on. The time frames will have to remain human though as far as we’re concerned. That could be on the order of thousands of years, although we need to work on that right away. Don’t expect a Star Trek galaxy. It’s a ludicrous idea on the face of it. Don’t expect something that looks primate like and builds machines that we would recognize. In fact don’t anticipate what we’ll find at all, it’s pointless. Just do the hard work of building the data set. Think how little we knew of our own solar system even 50 years ago. The knowledge acquired since 1970 is staggering and most of it completely unpredictable. That applies to the galaxy as well. Be prepared to be amazed and astounded :)

    • Robin Datta September 11, 2020, 0:28

      Intelligence is what one says it is. When tool use and toolmaking was described in animals, the definitions of intelligence were promptly revised at each increment of sophistication to exclude them. Mycelia sense and respond in a time and space framework quite different from ours, solving problems although well adapted to their niche in the ecosystem. A similar situation pertains to slime molds.

      If of a uncountable number of civilizations in innumerable galaxies one or two get to the sophistication to escape and survive their dying suns, that will be like the one or two bacteria that develop resistance and survive the deluge of antibiotics unleashed in sick humans: what emerges is a resistant bacterium, or a civilization that can survive the death of their stars.

      • Alex Tolley September 11, 2020, 13:29

        Intelligence is what one says it is. When tool use and toolmaking was described in animals, the definitions of intelligence were promptly revised at each increment of sophistication to exclude them

        The same applies to artificial intelligence. It was especially the case when Kasparov was beaten at chess, once considered one of the peaks of human intelligence. Fortunately we had Go, but that too has fallen to machines. OTOH cleaning dishes, teaching children in class, and a host of tasks deemed as “easy” and requiring almost no intelligence, has proven elusive tor “intelligent” robots.

        I do like your analogy of [Antibiotic] resistant bacterium, or a civilization that can survive the death of their stars being on the same continuum.

  • AlexTru September 11, 2020, 2:28

    … . It will eventually be our Encyclopedia Galactica.…

    SETI brings no scientifically significant data meanwhile, we have no signal detection meanwhile, and SETI systematically deny to recognize negative search results.
    so the chance to collect scientific data using SETI approach is exactly same as the chance to detect ETI , i.e. indistinguishable from zero.
    Encyclopedia supposed to contain information, SETI database is empty.

    • Alex Tolley September 11, 2020, 13:37

      On the contrary. As you point out in your comment below, that there are no easy to detect signals, high energy beacons lighting up the sky is of scientific value. It disproves one hypothesis and narrows down the theory space.

      Clarke once made teh analogy that we are as islanders using drums to communicate, not hearing big drums from across the water, despite there being radio transmissions everywhere. This is usually interpreted as we are using the wrong technology. Once we have teh requisite technology, the signals will emerge. But what if there is no exotic technology? Then the absence of drums would be indicative that maybe there are no other populations elsewhere (at least those that are saying, “we are here, signal back”.)

      • AlexTru September 12, 2020, 2:40

        By the analogy with drum communication is much closer to SETI issue than “haystack + needle”.
        It clearly shows that civilization based on “drum technology” is able to communicate and/or detect only relatively close neighbors.
        Exactly same problem exists with radio (EM waves) and SETI principles.
        If there is any civilization that use radio / EM waves in relative proximity (tens of light years) to the Earth, SETI and non SETI could detect it long time ago, for longer distances – SETI searches are useless.
        Radio and EM waves still can be successfully used for direct imaging of distant worlds , to get “telescope like“ images from reflected star light, but it is not the way of SETI, so our hope is new instruments used by radio/optical astronomy, but not SETI…

  • AlexTru September 11, 2020, 2:37

    By the way returning to analogy with searches of “needle in haystack“, according main principle that SETI was founded, this “needle” supposed to cry (using EM waves) to Universe: “Please, someone, find me!”
    That EM radiation extends “needle” dimensions to cosmic scale… And there supposed to be lot of such crying “needles”…
    Now returning to Fermi paradox…
    Will SETI sometime recognize negative results? Answer is – never…

  • Gary Wilson September 11, 2020, 12:21

    Let’s think about this with a little humility. Our tools are pitiful and our reach is tiny, but growing and changing. New tools will come along. SETI doesn’t try to hide its negative results. They have tried to understand the possible reasons for the results being negative so far, as have many others (including many on here). We have no idea of the frequency of occurrence of life (yet), let alone “intelligent” life. If humans didn’t exist on Earth would people say there is no intelligence on Earth? These questions won’t be answered in any short time frame and any answers we do get will be conditional (constantly changing with time).

    • Alex Tolley September 11, 2020, 13:42

      I think it is clear that earth would be considered free of ETI until at least the invention and use of radio. However, I do think that ETI would also be doing more types of analysis, and clearly there are signs of civilization if the planet can be viewed in detail by optical and IR telescopes, especially is a probe is nearby monitoring the planet. We are even at the point where sensitive instruments could detect the rapid warming of the planet and the increased presence of GHGs, a possible signature of technological life, albeit perhaps, not that intelligent.

      • Wojciech J September 14, 2020, 12:50

        It really depends on resolution their telescopes would have. In theory illuminated cities would be visible.

  • Gary Wilson September 12, 2020, 15:48

    I have never believed in the Fermi Paradox. I think the lack of ETI visitors on Earth already has a number of very reasonable explanations. One contributing factor would be that FTL drives are not possible, that in fact Einstein was correct. Mass cannot be accelerated to or beyond the speed of light and there are no destination controlled wormholes out there, or Alcubierre drives. The second line of reasoning has also been stated many times: that slowships are extremely expensive to build, carry high risk of not completing their voyage and may be out there in small numbers but none of them is headed toward Earth (lots of other interesting planets to visit in the galaxy). Machine probes offer a bigger challenge. Why have no machine probes visited us yet that we are aware of? Well, maybe we’re not that interesting and we’re number 1 billion on the list of places to visit on the galactic tourist bureau rankings :).

    • AlexTru September 13, 2020, 4:00

      Gary, I suppose the discussion here is not about: “is there, somewhere ETI”, but it is about can SETI (as it is today) detect ETI or not.
      Personally me suppose that SETI has very low chance (one event per Universe “live”) to detect alien signal, i.e. no chance.
      Traditional astronomy has multiple orders higher chances to detect ETI, because it try explore everything, without application of faulty anthropomorphic filter to the nature (Universe) laws.

  • Hamilton1 September 12, 2020, 19:02

    Very interesting as usual but I go back to the original point… the natives didn’t have any technology and yet Columbus appeared to them. So we cannot actually prove that developing our own technology increases the chances of detection – sitting here and doing nothing might be an equally intelligent tactic.

    • AlexTru September 13, 2020, 3:47

      I am sure “sitting here and doing nothing”, if “doing nothing” means – do not do SETI as it is today, it is more intelligent behavior…
      SETI activity do not (and cannot) provide any scientific data about anything.

  • Hamilton1 September 13, 2020, 13:54

    I’m not quite as cynical as you, but I remember Jill Tarter saying: ‘If we don’t search, we will never find out’. Not necessarily true.

    • AlexTru September 15, 2020, 3:34

      Our searches are not limited by SETI, SETI is microscopic part of scientific researches, if there is ETI, science will detect it, but this detection will be done by methods and instruments that are different from unrealistic+anthropomorphic SETI concept.

  • Gary Wilson September 13, 2020, 15:50

    With respect, the probability of one group of humans on the Earth having advanced enough technology to travel to and find another group of humans on the Earth is probably in no way comparable to the probability of Earth being visited by ETI in any time frame which includes humans in their technological era overlapping with ET’s in their technological era (we don’t know how long that will be, possibly quite short here on Earth and elsewhere due to the variety of filters we have already come up with). Machines may visit us or may have already visited us (in Lurker form) and that probability should be higher if our understanding of machines (especially of the Von Neumann kind) is shared by ET’s.
    AlexTru, you seem convinced SETI is not useful at all. I don’t know enough to be sure of anything when it comes to ET’s. SETI researchers can gather information and try to interpret it. The EM radiation arriving here is a free source of information (it takes huge amounts of money to build detectors and interpret data I know) so I say if you can afford it and you want to make the effort, SETI is just another means of collecting data of unknown value. If the galaxy remains silent to us it does tell us something. It tells us that currently in our time frame we can’t detect any signals in the EM frequencies and at the chosen locations we have searched. Surely if the search gets big enough and sensitive enough that may change? I don’t think we’ll end up being the only race to discover radio waves, lasers etc. Time is the most difficult factor to take into account. Unless there are literally huge numbers of ETI’s out there we may not overlap technologically with any of them over any reasonably likely time frame and then you have the travel time of the radiation to take into account. A truly gnarly problem of vast complexity. No wonder we haven’t detected anyone yet. Their version of I Love Lucy might be on its way to us right now, but with a thousand years left in travel time :).

  • ljk September 25, 2020, 11:23

Leave a Comment