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Looking for Lurkers: A New Way to do SETI

SETI, the Search for Extraterrestrial Intelligence, has kept its focus on the stars, through examination of electromagnetic wavelengths from optical to radio signals. But Jim Benford has been advocating that we consider near-Earth objects as potential SETI targets, prompted by Ronald Bracewell’s thoughts in a 1960 paper advancing the ‘sentinel hypothesis.’ A Bracewell probe could linger in a target system for millions of years, monitoring developments on worlds with the potential for life. Couple that thought with the rarely studied co-orbital’ objects that approach the Earth both frequently and closely and you have a map for a realm of SETI that is only now coming into investigation.

What follows is a news release from The Astrophysical Journal covering Benford’s new paper, one we discussed on Centauri Dreams back in March [see A SETI Search of Earth’s Co-Orbitals]. I want to get this out now because Benford will be delivering the 2019 Eugene Shoemaker Memorial Lecture tomorrow, Thursday September 5, at 1900 MST (0100 UTC). The lecture, at Marston Exploration Theater in Tempe, AZ can be accessed online at https://asunow.asu.edu/asulive. For those not familiar with it, the Shoemaker Lecture has been set up by the BEYOND Center for Fundamental Concepts in Science as a special award to a leading scientist to honor the life and work of Eugene Shoemaker who, together with his wife Carolyn, pioneered research in the field of asteroid and comet impacts.

The most recently discovered group of rocky bodies nearby Earth are termed co-orbital objects. These may have been an attractive location for extraterrestrial intelligence (ETI) to locate a probe to observe Earth throughout our deep past. Co-orbital objects approach Earth very closely every year at distances much shorter than anything except the moon. They have the same orbital period as Earth. These near-Earth objects provide an ideal way to watch our world from a secure natural object. Co-orbitals provide resources an ETI might need: materials, constant solar energy, a firm anchor, concealment.

Co-orbitals have been little studied by astronomy and not at all by SETI or planetary radar observations. James Benford has proposed both passive and active observations of them as possible sites for ET probes that may be quite ancient.

A ‘Lurker’ is a hidden, unknown and unnoticed observing probe. They may respond to an intentional signal and may not, depending on unknown alien motivations. Lurkers would likely be robotic, like our own Voyager and New Horizons probes.

Long-lived robotic lurkers could have been sent to observe Earth long ago. As they would remain there after their energy supply runs out, this is extraterrestrial archaeology. If we find nothing there, this gives us a profound result: no one has come to look at the life of Earth, which has been evident in our atmosphere’s spectral lines over interstellar distances for over a billion years.

Co-orbitals are attractive targets for SETI searches because of their proximity. Benford thinks we should move forthrightly toward observing them, both in the electromagnetic spectrum of microwaves and light, and planetary radar. And we can visit them with probes. The most attractive target is ‘Earth’s Constant Companion‘ 2016 HO3, the smallest, closest, and most stable (known) quasi-satellite of Earth. Getting there from Earth orbit requires little rocket propulsion and can be done in short trips. China has announced they are going to send a probe to 2016 HO3.

The well-regarded astronomy journal of record, Astrophysical Journal, is publishing Benford’s paper “Looking for Lurkers: Co-orbiters as SETI Observables” in the near future.

This is the latest in an agenda Benford has carried out in imaginative searches for interstellar communication. His first work with other family members yielded the term ‘Benford Beacons’—short microwave bursts to attract attention, like lighthouses. Later he pointed out the uses of powerful electromagnetic beams to send light spacecraft, ‘sails’, in interplanetary exploration. His Lurkers proposal moves on to actual relic alien spacecraft that may have been nearby for longer than humans have existed.

Interstellar travel is challenging – no craft engineered by humans has yet traveled further than the outskirts of our own Solar System. One project working to change that is Breakthrough Starshot, which aims to send a gram-sized spacecraft to a nearby star system at around 20% of the speed of light. “Within the next few decades we hope humanity will become an interstellar species,” remarked Breakthrough Initiatives Chairman Dr. Pete Worden. “If intelligence arose elsewhere in our galaxy, it may well have sent out similar probes. It’s intriguing to think that some of these may already have reached our own Solar System.”

The paper is Benford, “Looking for Lurkers: Objects Co-orbital with Earth as SETI Observables,” soon to be published by the Astrophysical Journal (preprint). To attend Benford’s lecture at the University of Arizona online, the address is https://asunow.asu.edu/asulive.


Comments on this entry are closed.

  • ljk September 4, 2019, 13:56

    And isn’t it funny what a recent paper has determined the shape of Oumuamua to be: A thin, flat disc….


  • Thomas Goodey September 4, 2019, 14:42

    I am surprised that Benford should make this proposal. It’s not true that “these near-Earth objects provide an ideal way to watch our world from a secure natural object.” First, they are not at all secure. These so-called “quasi-satellites” are not in stable orbits relative to the Earth, even at the thousand-year scale which is very short in this context. They cannot be relied upon as long-term platforms. Second, the logic of “co-orbitals provide resources an ETI might need: materials, constant solar energy, a firm anchor, concealment” is unclear to me. If ETs can get from another star to here, they are not likely to be short of materials, which can be obtained from any suitable asteroid in our system (and there is no particular reason to think that the co-orbital body would have the right sort of material available). The solar energy is not constant – they rotate just like everything else. And of what significance is the “firm anchor”? The co-orbital is spinning round and round!

    • Paul Gilster September 4, 2019, 16:02

      Although horseshoe orbits appear shorter-lived, my impression has been that other co-orbital options like ‘tadpole’ and ‘quasi-satellite’ orbits are far more stable, but that in any case, the question of their long term stability has not yet been settled. Given the certainty of your statement that these orbits are not stable, I’d be interested in your information sources. I’m not aware of a definitive paper on the matter. Benford surveyed what’s out there in his paper, which I linked to in the article. From it:

      “The long term stability of these objects is an area of substantial study [12-15]. A large number of horseshoe co-orbitals of Earth, quasi-satellites, Trojans and horseshoe orbits, appear to be long-term stable. Morais and Morbidelli, using models of main asteroid belt sources providing the co-orbitals and their subsequent motions, conclude that the mean lifetime for them to maintain resonance with Earth is 0.33 million years [16].”

  • Patrick Underwood September 4, 2019, 15:26

    Wondered about this for a long time. (Maybe I picked it up reading brother Greg’s novels!)
    I always thought of it like this: If we sent a geostationary spy satellite back a century in time, there’s a good chance no one would detect it. They certainly wouldn’t be able to say it’s a camera in orbit, watching them. So imagine the trouble we might have, trying to detect a Lurker from a star-faring civilization. If they don’t want to be found, we’re not likely to find them.
    The Moon would make a good base for observations, as well, if the Lurker is buried/camouflaged.

    • H. Floyd September 4, 2019, 16:03

      I read somewhere that the Tycho Impact Crater would make a tantalizing location for one of those.

      • Alex Tolley September 4, 2019, 19:12

        Indeed. ;) In all seriousness, I don’t know why the Moon is not the best location. It is stable, the Earth reliably stays visible and twirls around every 24 hours to provide a global view. The vast landscape provides the best opportunity for “hide in plain sight” with all the clutter to explore. And if the lurker decides that just maybe it should make itself known, well a huge magnetic field should be just the ticket…

        • Richard Burke-Ward September 5, 2019, 9:36

          Lunar “exo-archaeology” is something that Alexey Arkhipov has been advocating for at least 25 years:

      • Patrick Underwood September 4, 2019, 20:25

        Howdy, Heywood!

  • Alex Tolley September 4, 2019, 16:21

    While I applaud the idea of at least starting to look for ETI in our backyard now that SETI has not found any obvious sign of radio communication, I find the logic of the posted text poor. The preprint paper is better, but the search logic is also flawed, IMO.

    If we find nothing there, this gives us a profound result: no one has come to look at the life of Earth, which has been evident in our atmosphere’s spectral lines over interstellar distances for over a billion years.

    This is not a logical statement. One cannot use a particular and generalize, i.e. the possible locations of lurkers are far larger than these co-orbitals.

    The most attractive target is ‘Earth’s Constant Companion‘ 2016 HO3, the smallest, closest, and most stable (known) quasi-satellite of Earth. Getting there from Earth orbit requires little rocket propulsion and can be done in short trips.

    This is a bit like the joke of the person who lost his spectacles in a bush, but hunted for them under the streetlight, because: “that is where the light is!”. Certainly, start somewhere, but why the easiest place first?

    The underlying assumption is that a Lurker is hiding on/in a natural body, or is camouflaged to look like one (a hide). This is unwarranted. We already have radar stealthy aircraft with our primitive technology. We could place a B2 or F-117 in space and it would be all but undetectable. The co-orbital orbit may be an attractive location for a lurker, or it may not. But looking for one on a detected body may be as pointless as looking for a stealth aircraft on Mount Everest. It is often assumed that Von Neumann replicators must be close to a raw material source to achieve its replication task. However, a lurker may only ever need material on rare occasions, in which case it can go to one, collect the material and depart. Examining a target asteroid at best might reveal signs of mining that haven’t been carefully hidden.

    To repeat, it is high time we search for such lurkers. It may even be that the search strategy selected is the best one to get funding – it can piggyback on a science mission. However, it may be such a search is like looking for ancient buried cities by joining an oil exploration mission or a fossil-hunting expedition in the Sahara. One might get lucky, but probably not (even assuming a lurker or its dead remains even exists).

  • Geoffrey Hillend September 4, 2019, 17:06

    The idea that if we don’t find dead lurker probes is not enough evidence to prove that we have not been visited by ET spacecraft in our past. They don’t sent only probes to our world . If ET’s landed on our planet in our past and left no trace, we would never know they were here A civilization with interstellar travel spacecraft technology would not be limited to lurker probes. What kind of technology would a civilization one billion years more advanced than us have? That is a long time.

    I do like the idea that they could study us without us knowing. Maybe those probes don’t die or they can return to their planet. If they can get here, they might be able to leave. The belief that they could not leave is limited to today’s technology, but not the technology of our future.

  • Geoffrey Hillend September 4, 2019, 17:31

    The space age has only been around for fifty years and accurate radar technology since world war II. One billion years minus eighty years is 999,999,999,920 years of our sky’s without radar surveillance.

  • Geoffrey Hillend September 4, 2019, 17:32

    Excuse me that 999,999,920 years of our sky’s without radar surveillance.

  • Mike Serfas September 4, 2019, 20:35

    The superset of alien archaeology seems more interesting. I don’t think I need to ask if you were thinking what I was thinking when the bright spot on Ceres first came into Dawn’s sights. Each of the innumerable dull, dead, airless bodies of our Solar system represents a chance to stumble across some long-lost quarry or treasure trove.

    I think the Venus co-orbitals should be more interesting for a first glance. They lack the competition of a Moon, and there is no telling what they might have been used for a billion years back, before that planet was resurfaced in what perhaps was an avoidable exercise of global warming.

    • ljk September 5, 2019, 9:26
      • Mike Serfas September 5, 2019, 18:15

        A fascinating phenomenon. Iron, sulfur, and organic metabolism floating around near the sweet spot in Venus’ atmosphere with near STP. At the same time … any lifeform there would seem to be living in the middle of a Friedel-Crafts alkylation. I can’t imagine what is biochemically feasible under such strange circumstances, but with this data it seems like a very interesting place to look for very non-Earthlike life forms.

      • Robin Datta September 6, 2019, 2:12

        If Cytherean microbes were to pan out, that would be a welcome reset to Fermi’s Paradox while opening up a can of panspermia worms!

  • Geoffrey Hillend September 4, 2019, 21:18

    After reading this paper more carefully, I see they are talking about co-orbitals. Gram sized spacecraft might be challenging to locate even with radar since they are so small. Quote by Allex Tolley. “We could place a B2 or F-117 in space and it would be all but undetectable.” Stealth planes have a range limit, so they have to be at least thirty miles or more from the radar receiver to remain undetectable. A B2 or F-117 would be completely undetectable by radar it was a co orbital or outside the orbit of our Moon. Any type of spacecraft or probe from that distance which uses stealth technology would be completely undetectable.

  • Geoffrey Hillend September 4, 2019, 21:51

    I am thinking that stealth technology with RAM radar absorbent material which is invisible to some radio frequencies could be detected with infra red light. A infra red laser which makes in invisible infra red wavelength black body beam could be used to light up an object that was far away and observed with an infra red telescope, but that could be defeated with black silicon which absorbs infra red. The color black is also a low observable in the visible spectrum in space.

    We might have take a spacecraft with remote sensing technology and go outside the orbit of the Moon to find the lurkers. It cant hurt to look though since no one is looking there now, but I agree with Alex Tolley, that if the lurkers were using stealth technology, we would not have a chance of using remote sensing to find them from Earth. We would have to go out into the area where they are in space to see them.

  • Richard Burke-Ward September 5, 2019, 10:22

    It’s a truism that any human attempt at SETI is anthropomorphic. One way or another, we are always going to be searching for some variant on “what we would do” – or on what we technologically *can* do. And that’s not only natural, it’s valid: we don’t know how else to look, so let’s at least look in the ways we can imagine. It’s better than not looking at all.

    I’m a firm believer (and long-term advocate) of searching for artefacts in our own backyard. Three reasons: there is a non-zero probability of finding something; leaving probes around celestial objects of interest is something that we do and therefore there’s a small chance that other intelligences might do likewise; it’s a search that lies within our technological grasp (in a limited kind of a way). However…

    Talk of stealthing and resource management and orbital convenience seem to me to be at best half the story. Those are the things we can imagine – and therefore they are valid ways for us to search. But we are potentially dealing with entities (flesh / machine / other) that are either indistinguishable from magic, or indistinguishable from reality given our limited perceptual / cognitive capacities. I’m not getting mystical here; what I mean is, how could we tell?

    Is a space rock really a rock? To all our available means of testing, perhaps yes. But that doesn’t mean it isn’t something else as well. An uncontacted Amazonian tribe might assume a musket was some form of club – hold the barrel, hit ’em with the handle. There may be forms of ETI (or machine emissaries of such) that are right under our noses but we fail to interpret them for what they are. Worse, they might be baffled by our failure to understand…

    Think of the general trends of our technology: greater energy density, greater information processing density, molecular control moving towards atomic control, signal efficiency moving ever closer to apparently random noise, diminishing waste from technological processes, increasingly fine control over our own biology, increasing ability to mimic nature… Now take these trajectories a decade or two into the future: drones that are indistinguishable from insects, signals that are undetectable in transit, computer-brain interfaces, and more…

    And now take *those* trajectories and imagine a thousand years of that same kind of progress. We’re in Arthur C. Clarke land: our future technology could easily be indistinguishable from magic. But it could equally well be indistinguishable from the world around us. Unless you happened to be able to tap in to these processes and technologies, you just wouldn’t know they were there.

    Now take *those* trajectories, and imagine a similar but utterly alien timeline. And then project that timeline out a million or even a billion years. Then assume that one way or another, that technology has arrived in our solar system – a probe, if you will, an entity with amazing technological resources and a desire to… well, do whatever such entities want to do. Your next door neighbour could be an alien construct, and you’d never know. There could be a nano-scale machine in orbit that is trying to make contact with our traffic management systems and is baffled by its failure to respond…

    Above all, there could be some tiny minority of the people who have reported seeing something deeply strange where the underlying phenomenon could, in fact, have an extraterrestrial origin.

    Trouble is, any scientist or politician who espouses this view (and remember I’m not saying “We know these things happen”, I’m saying “We can’t be 100% sure that these things *don’t* happen”) will get shot down in flames by colleagues desperate not to be associated with anything that sounds flaky. And I totally get that. I mean, ‘flaky’ is the ultimate scientific insult. But what if it’s *not* flaky? What if it’s reasonable to keep an open mind? Humanity’s group-think mentality is potentially damaging in the face of such questions.

    In my opinion, picking up rocks and examining them is an important thing that we can and should be doing. But if we’re looking for *special* rocks, there’s a chance that even so, all we will see is… well, rocks.

    So, IMO, keeping an open mind – even to unorthodox ideas, even in the face of anxiety about future funding, respect of peers, etc – is the very best thing we can do.

    Because that may yet turn out to be the most unique and valuable asset that our species has.

    • Thomas Hair September 5, 2019, 22:50

      Richard, you just posted one of the best comments I have ever read on this forum. Outlier thoughts and ruminations that have a non-zero probability of occurrence should be contemplated. If we contemplate enough of them, we might reveal a deeper reality.

      • Richard Burke-Ward September 15, 2019, 5:20

        Hi Thomas – and you just summarised very neatly in two sentences what I waffled about for several paragraphs! Thank you!

  • Neil Stahl September 5, 2019, 11:02

    It pretty clearly depends on “their” technology (which shouldn’t be shabby if they got here and are engaged in this) and our technology (probably far poorer than theirs) and how much money we’re willing to spend on this (probably not much) so I don’t think we can conclude anything if we don’t find anything. Much like the SETI effort in general. Probably worth a try but only a big deal if we actually found something, then a very big deal. So I’m for it.

  • Alex Tolley September 5, 2019, 11:44

    The Lunar Reconnaissance Orbiter has a camera resolution of about 0.5 meters per pixel. It can clearly show the descent stage of the Apollo LM and even some of the experiments.
    Apollo 17 landing site.

    But consider that a 0.5 m pixel is just 1 of 1.6e14 pixels mapping the lunar surface. A black F-117 sitting on the surface is about 1000 pixels, which would make a machine search quite easy. But if it was camouflaged. or buried so that it wasn’t visible, it would be unnoticed by even the LRO. Even if there was enough steel in the airplane, any magnetic signal would be lost amongst all the metal meteorite impactors’ signals. My conclusion is that a lurker could easily be observing us from the Moon yet be overlooked.

    Now consider the volume of space that must be searched in one of these Earth co-orbits. Even the Lagrange points L4 or L5 has volumes far larger than the Moon, and the entire volume, not just some boundary surface must be exhaustively searched with sensors that will not be defeated by camouflage, or stealth. As I noted earlier, a dark, stealthed aircraft positioned out there would be next to impossible to detect without good radar inspecting small volumes of space. If the lurker has to be easily detectable to be found, why does it even need to lurk in those locations?

    I repeat that we should make the effort, although I suspect that the search will prove fruitless. Any such probe of a Bracewell type could really be anywhere in the solar system, depending on its capabilities and purpose.

    As Douglas Adams said: “Space is big. You just won’t believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space.”

  • Gary Wilson September 5, 2019, 13:15

    Are we really that interesting? A quick look by an extraterrestrial species would tell them enough. Ahhh, they’re at Stage 1c: over consuming their limited natural resources, continually at war with one another, in denial about their destructive capacity, greedy, violent, selfish, unwise. Yes they need to be placed in secure containment for the next 100 years. No contact of any kind shall be initiated. We’ll check to see if they’re still around in a century. I’m only partly joking here. If lurker technology from an advanced society exists we won’t find it and ET wouldn’t need to waste it on us. And has already been argued we probably wouldn’t even know what to look for if they are even hundreds of years ahead of us technologically. The odds of this being a worthwhile endeavor are exceedingly low. Let’s use our limited resources on improving the sustainable habitability of the planet as well as studying what we find out there.

  • Gregory Benford September 5, 2019, 13:45

    Comments here make big assumptions about alien motives & methods & then follow them along. But we’re ~300,000 yrs old and gave no sign of our society until recent tech. So a bio explorer is far more plausible than a stealth observer. Look for ruins of those on nearby bodies, not distant asteroids. & recall any subtle gear must be carried at great cost from distant stars. Jim & I have some work along these lines we hope to present in a later paper. Meanwhile, watch his talk tonight!

    • Alex Tolley September 5, 2019, 19:46

      So a bio explorer is far more plausible than a stealth observer.

      Then why the need to “lurk” at a distance? Lurking implies concealment and furtive movement. For a craft doing a reconnoiter for life, possibly taking samples for analysis, why the need for concealment in space? Most living worlds will not have a technological species capable of detecting the craft. The craft could sit in a close orbit, drop landers for samples and analysis.

      But the stated assumption is that the craft must conceal itself from technological species. How would this be consistent with a “bio explorer”, rather than an observer of technological civilization? If the probe is to be rather monolith -like and [eventually] respond to an em signal, why make it so difficult by sitting on/in a distant small asteroid rather than be very close by in orbit or on the Moon. We can reliably target em signals to the lunar nearside without needing to know the probes precise location. It would be more like vocal signaling in a forest, rather than visual signaling.

      I agree we cannot know ETs motives (so why assume “bio explorer”) but this proposal seems more like selecting an astronomical target and then trying to fit ET’s motives and technology to select that target. The comments on this and the prior post are mostly directed at examining that logic. AFAICS, neither Benford attempted to justify the argument for a co-orbital location.

      I look forward to hearing any lecture audience questions and responses in this regard.

      • Mike Serfas September 6, 2019, 14:54

        The concealment could be incidental to other attitudes. If you go for a hike in the forest, do you leave plastic containers behind? Alien biologists might well have left evidence on Earth, but made it biologically or environmentally degradable out of habit or a generic sense of propriety. A disinterested reason for concealment also allows for an incidental reason for lack of concealment. The same explorers, tapping asteroids for building materials or propellant (if they stoop so low), might not bother to cover their mines under the rationale that once one has decided to use up their natural resources, the cosmetics are meaningless. (Making the mines small, on the other hand, would be a priority!) For an interstellar culture, asteroids are certainly not inaccessible: they are at a higher more convenient location, and machines can dig them unperturbed by weather and without ruining the ecological data.

        • Alex Tolley September 6, 2019, 16:38

          Leaving trash in a forest is the theme of “Roadside Picnic”. However, concealment by deliberate stealth would be equivalent to wearing camouflage on your hike. Aren’t camouflaged people in a forest mostly hunters (of animals or people)?

          • Mike Serfas September 12, 2019, 18:18

            If they haven’t started shooting yet, let’s hope they’re cameramen from National Geographic.

    • Richard Burke-Ward September 15, 2019, 5:38

      Gregory, you say “recall any subtle gear must be carried at great cost from distant stars”. But surely this is false. If we were a little more technologically able (and if ETI is close by in some form, then they are clearly more technologically able than us), then we wouldn’t send a finished machine across interstellar distances, we’d send a much smaller machine that could construct the machine we ultimately wanted using local resources. So, we’d send something the size of (say) a toaster, which could then use local materials to construct something the size of a city.

  • Alex Tolley September 5, 2019, 14:40

    Although we clothe SETI in scientific rationale, it often seems to me that is little more than the age-old desire to have powerful gods reveal themselves to the worthy. These gods are believed to reside somewhere (Mt Olympus, Heaven), and that they observe us mortals and sometimes interact with us, and that they can be found by heroic journeys or deeds or just worship. By making contact, or journeying to their artifacts in space, we are hoping for a contemporary version of receiving Prometheus’ fire.

    We assume that ET probes are more understandable to us that a human taking wildlife video from a hide is to the observed animal. Yet this may be our cultural blindness. As Lem suggested in “His Master’s Voice”, any ET artifact may be effectively inscrutable to us. (cf the “gel” found on the lunar Farside). Or the Strugatskys’ “Roadside Picnic” where artifacts may be intelligible, but of mostly unknown purpose and may even be deadly.

    A technological ET civilization perhaps near our technological capabilities may be quite unintelligible to us, with completely alien cognition and behavior that would make communicating with insects seem simple. But ET thousands, millions, or billions of years more advanced? We have enough difficulties understanding our human ancestors of just thousands of years ago. One really has to buy into the idea that science and technology will create some convergent common ground between humans and ET. To paraphrase Haldane : “ETs are not only stranger than we imagine, they are stranger than we can imagine”

  • Patrick Underwood September 5, 2019, 16:24

    There are many rabbit holes we might go down–we’re living in a sim, aliens are potentially unknowable, we’re in a zoo with a deliberately altered view of the surrounding universe, alien probes might be undetectable nanomachines or worse–but we can only do what we can do, right? Doesn’t hurt to look.

    The Fermi Paradox tells us something weird is going on. At our present level of development, it makes perfect sense that if we could, we would expand humanity across the galaxy, in a way vastly obvious to any alien observer. The fact we don’t detect anything similar is shocking and disconcerting (at least to me!). Perhaps Iain Banks’ “subliming” is really a thing. But that doesn’t (necessarily) preclude leftover artifacts from the “pre-sublimed” era of a sublimed civilization.

  • AlexTru September 6, 2019, 3:39

    …>>If we find nothing there, this gives us a profound result: no one has come …
    I like this typical SETI argumentation :-) It means that we will never get negative result, so “must” continue searching “till the end of Time”…
    For those those who in any case interested in this “SETI-archeology” efforts I have a good news – if there is something , it will be found, but nit by SETI, but human space exploration activity (geology, biology etc.).
    There is no need to spend even 1 cent for Astro archeology activity till we will find some unusual artifact as sub products of traditional space exploration.

    • Alex Tolley September 6, 2019, 16:53

      I disagree. In a historical context you are suggesting that expeditions should only have hired the specialties for the purpose of the expedition ( e.g. Mapping territory) and not scientists who were peripheral to that task. We need to be prepared to find the unexpected, and that means expending some resources and effort.

      We are not going to find ancient ruins on asteroids, but we might find some unusual phenomenon that would need a practiced eye to discern. Recall that the later Apollo astronauts were trained to be rough and ready field geologists so that they might be more prepared to find the samples the scientists back on Earth really wanted. That proved a very successful strategy.

      Can you imagine if the astronauts only mentioned that they saw some “interesting” rocks but didn’t collect them, because NASA could send a geologist on some future trip?

  • Brett Bellmore September 6, 2019, 6:16

    These bodies are worth examining quite aside from SETI, being both a collision hazard for Earth, (So that the orbits of all sizable ones should be characterized ASAP.) and relatively low delta-V accessible space resources.

    I could see one of these supplying radiation shielding for a Earth-Moon or Earth-Mars cycler, for instance.

  • Gary Wilson September 6, 2019, 13:46

    I believe microbial life will be common, multicellular life less so, intelligent life rare. That means a relatively small number of intelligent species in the entire galaxy spread over billions of years of time. Many don’t want to accept that species have life spans. A successful intelligent species may only last thousands to hundreds of thousands of years. So that means very little likelihood of contact in a galaxy the size of ours. Add to that the high probability that light is in fact the ultimate speed limit. So no cheating with FTL drives! Be prepared to find nothing leading to ET for a very long time indeed. Isn’t that what we’re already beginning to suspect?

  • Geoffrey Hillend September 6, 2019, 17:14

    I like Alex Tolley’s idea that we think the ET’s are going to give us the Promethean fire. If a civilization is much more advanced than us, I don’t think they are going to give us their technology. It would be interfering with the technological development of a civilization, the old prime directive of Star Trek; It would be cheating us out of the opportunity of inventing our own interstellar technology. Carl Gustav Jung wrote that whenever the technological development of a civilization progresses too far ahead of it’s psychological development, there are wars. Consequently, the lurkers don’t hang around to be captured. Stealth technology would explain this. One is not going out there to look for something if it does not appear from Earth, an underestimation our technological capabilities and the ET’s technology.

    Also Jung wrote in his book Flying Saucers, a modern myth, that FTL would be a physicists miracle since what is impossible today will be possible in the future, for what was considered impossible in physics in the past is possible today which is why it important to be future oriented in one’s thinking about ET interstellar travel technology which must include today’s technology, but always is much more advanced than ours. Stealth aircraft technology is a recent development of the late 20th century.

    We also have access to our own Promethean fire, the scientific intuition and inventiveness can considered to be a universal function of all intelligent life’s mental perception. It takes time to steal the Promethean fire, but if we are willing to wait and work for it, one day our physicists will steal a lot of it. The Jury is still out on FTL technology.

    • Charley September 7, 2019, 14:30

      I doubt we have not to actually steal Promethean fire, but rather wait till God reveals that to us in due time. It’s just my feeling that divine intervention in the inspired creation of the human intellect is what will solve so many problems, but of course so many problems are of a moral and spiritual dimension not technological.

      It’s very difficult to say to what degree the ETI will or will not want to observe any particular planet and how they would do it, but suffice it to say they’ll probably be pretty clever about it. After all, if you can achieve star travel, then probably doing reconnaissance is almost mundane by comparison. I’m still pretty much of the opinion that we are alone here, perhaps in the Milky Way but with regards to the larger universe as a whole, perhaps in another galaxy someone else out there got intelligent and is also in the process of interstellar travel. Kudos to them if they can find a way to jump across the vast distances that surround each and every galaxy.

  • Gary Wilson September 7, 2019, 15:02

    Very interesting comment Geoffrey. The jury will always be out on FTL travel until it happens. I just tend to think it isn’t going to happen in time to help us. And it won’t help with the key questions anyway. What intelligent species completely fouls its own nest? How bad does it have to get before we do something serious about it? There is evidence that we are threatening the survival of the ocean phytoplankton now with increasing acidification of the oceans. That and burning down the Amazon, and destroying the key global fishing zones. Better start doing something if we are going to survive long term and have some chance of eventually developing FTL technology. Sorry to sound like a broken record but the time for action is now. Irreversible climate damage by 2030. Do whatever you can to help and spread the word.

  • Alex Tolley September 7, 2019, 15:03

    A different direction to look for ET?

    Foundations of Interstellar Studies Workshop

    Precis of the presentation by Greg Matloff:

    Is the Kuiper Belt inhabited?
    Greg reminded the audience of the Fermi Paradox,
    but then noted that if intelligent aliens had
    encountered our solar system, they would get to
    the Kuiper Belt before they got anywhere near theplanets. And the Kuiper Belt is resource rich, so
    might they have chosen to settle there, rather than
    come to visit Earth? Our biosphere might well be
    poisonous to them anyway, given that although
    there are around 230 amino acids in all, life on
    Earth only uses around 10 % of them, so the
    likelihood of a perfect overlap with alien biology
    is small. Greg also noted that recent observations
    by ESA’s Gaia space observatory suggest that
    our solar system is approached to within around
    one light year by another Sun-like star roughly
    every million years. Given this, might a suitably
    advanced and long-lived race of extraterrestrials
    wait until the next close approach before ‘hopping
    across’ to the neighbouring star system? Greg
    pointed out that if such a civilisation did this, and
    thus doubled the number of star systems they had
    visited every million years, they would be in more
    than one billion star systems after thirty million
    years. In the light of this, Greg suggested that
    it would be worth surveying the Kuiper Belt in
    the infrared and visible wavelengths, looking for
    emissions from a functioning alien outpost, or for
    unusual Kuiper Belt Objects that might represent
    the remnant megastructures left behind by aliens.
    In this regard, Greg mentioned three anomalies
    we are already aware of: Saturn’s moon Methone,
    which looks almost exactly like an egg; Ultima
    Thule, whose two lobes are strangely flat; and the
    interstellar asteroid Oumuamua, which is long and
    thin and has also, unexpectedly, been speeding up
    as it leaves the solar system. Greg concluded by
    noting that if we do explore the Kuiper Belt, but
    find no evidence of past or present extraterrestrial
    visitation, this would also be an important result, as
    it would strengthen the argument that we truly are

    Source: Principium Journal #26. August 2019

  • Geoffrey Hillend September 7, 2019, 18:25

    I am still biased against the idea of finding alien technology. I’m all for looking though. The idea seems too old school and science fiction. Earth is where the action is so why would aliens leave behind technology so far away from us. I am all for looking into the sky with infra red, but I suggest also looking a little closer like the co-orbit, or the Lagrange points as Alex Tolley has suggested or maybe even closer like the Moon or between the Earth and the Moon. If we find nothing we can go closer.

  • wdk September 8, 2019, 13:59

    There is no denying that these issues are entertaining.

    Going back a ways in the comments regarding lurkers in the NEOs. The question of stability was examined on the basis of early arrivals to the terrestrial scene with respect to the ascent of human activity or prominence.

    Whether near Earth objects are stable or not, if we assume something has been around for, say, 300,000 years, that pre-supposes a great deal of expectation about the terrestrial environment, considering that our ancestors were struggling with scraping stones. If we are assuming that the NEOs would be their lairs, then it is good to remember that some NEOs do break loose and collide with Earth or the Moon or get their trajectories perturbed considerably. So should we priortize the demonstrably stable NEOs and consider them unnaturally so or odd?
    Or should we assume that perturbed NEOs have been “reassigned”?

    So assuming that this procedure was adopted:
    1. We’ll just place a probe in a NEO, because that’s what we always do when stopping by at world with biota that has several or more cells?
    ( But still, would have to wonder what the threshold would be for
    that guarded of an approach).
    2. We’ll just place a probe in NEO, because we were down dirt side and had a chance to converse with those chaps…
    3. And what if there weren’t any good NEOs available in a system?

    On the other hand, the inspectors could simply walk through a door in the air or step out of a levitating craft and get all the first hand data that they need, any time, any geological era…

    It’s not that we don’t have any detection capability. In fact we do.
    The moon, beside being a great observation deck, is one that leaves
    a lot of traces. Unless we assume that game wardens clean up for all the passers-by that land and have picnics there. I mean, do they all abide by the same stealth agreement?

    One of the earliest Space Shuttle missions was the deployment of the Long Duration Exposure Facility (LDEF) and its exposure was several years longer than anticipated after the Challenger crash. But it was retrieved and the dust and orbital debris collisions on its exposed surfaces were examined. …How much do you suppose was traced back
    to ET spaceships? Nada. But there were paint flecks and solid rocket exhaust traces…

    I’d say that the best arguments for ET contact are all the anomalous stories in the files that had instrumentation trained on them or there were retrieved samples. How many really exist I don’t really know and some might not even be recognizable as yet. But likely as not, if we ever get any traction on the truly abnormal and the abnormality was extra terrestrial, they might take us in unexpected directions. E.g., which would be harder for us to accept physically: a visitor from an earth-like world a thousand light years away or a sentient creature from Jupiter? In the latter case, I suppose, be on the lookout for weird critters in terrestrial diving bells. But don’t touch, because should they explode…

  • Ljk September 8, 2019, 17:43
    • Alex Tolley September 9, 2019, 0:14

      Without reading the paper, my critique is that the L-V equation assumes no search time to find prey. This works on Earth, but for c-limited replicators That won’t work. So Forgan must be assuming populations of predators and prey confined to each system. That isn’t very interesting other than as a way to limit replicators which could be limited in other ways such as limiting replications for each new replicator. I would much rather see galactic populations with few probes per system and complete predation per system when the predator arrives.

  • NS September 9, 2019, 4:22

    An oldie (1984) but a goody: Robert A. Freitas refutes the Fermi Paradox:


    • Alex Tolley September 9, 2019, 12:28

      There’s aliens Out There, yessir, and I, for one, am going hunting for them. We haven’t looked nearly hard enough, or long enough, to spot any of them yet. But we will.

      And maybe sooner than you think.

      35 years later there is still no sign of ET.

      However I do like this idea:

      Astronomers have found that unless the galaxy is about ten times heavier than it appears, there’s not enough gravity to hold it together. If it does hold together, then where is the invisible “missing mass” hiding, perhaps 90% of the total? Could it be dammed-up star-stuff, stored in giant depots near Dyson spheres surrounding the remnants of the vast majority of stars in the Milky Way? At present, we have no way of knowing.

      Now there is an interesting explanation for dark matter!

  • ljk September 10, 2019, 16:44

    Somehow it feels appropriate to put this here:



    We may have our second interstellar visitor. And this one may be visible for a lot longer than Oumuamua. Fire up a probe stat!

  • ljk September 11, 2019, 16:25

    Sky & Telescope’s take on our new visitor. It seems to have a tail:


  • ljk September 12, 2019, 15:19

    When it comes to representing ETI to humanity, religion cannot be ignored, even in the early 21st Century:


  • mick September 13, 2019, 14:29

    Can we perhaps hope that the Lurkers plan to intervene and stop the human race from screwing up the Earth completely? (Dream on, Mick, there ain’t no space cavalry a’comin’, it looks like it’s “heads between legs time” for all of us, folks).

  • Mike Serfas September 14, 2019, 19:30

    Speaking of stealth … https://phys.org/news/2019-09-blackest-black-material-date.html Absorbs 99.96% of light from any angle. If a “Lurker’s” stealth is accidental because our friends just really love to absorb photons for energy, maybe they’ve neglected to paint the stars back onto the sky, and exoplanet hunters will stumble across this handiwork any day now.

    • Ron S. September 15, 2019, 11:43

      99.96% is -34 db (or less than 9 astronomical magnitudes, if you prefer). That isn’t much. It is only helpful if there is adjacent radiation that submerges the signal below the surrounding “noise”, and the noise cannot be filtered (situation dependent). Similarly, any directed transmission from the lurker requires exquisite eradication of antenna minor lobes to achieve a similar degree of imperfect cloaking. Going dark isn’t easy.

  • Michael C. Fidler September 19, 2019, 21:48

    China’s Lunar Rover Scopes Out Weird Substance on Far Side of the Moon (Photos).

    Take a look at these two images! I did a color enhancement that shows the outline of the green object and looks to be about book size – 8×11 inches. Two interesting unusual objects appeared in the enhancements, the red circle centered in the middle of the gel and in the wide field view a blue area that reaches from the object toward the rover. This all looks like either a well orchestrated hoax by the Chinese or they were very lucky to find an alien or earthly artifact!





    • Paul Gilster September 20, 2019, 6:55

      I doubt it’s either. From the Space.com article:

      “The compressed, black-and-white shot comes from an obstacle-avoidance camera on the rover. The green, rectangular area and red circle within are suspected to be related to the field of view of the Visible and Near-Infrared Spectrometer (VNIS) instrument, rather than the subject matter itself, according to some lunar scientists.”

      A lot to untangle about this story, so I wouldn’t jump to any conclusions.

  • ljk September 24, 2019, 10:09

    We keep looking for space aliens. Are they looking for us?

    September 23, 2019

    Seth Shostak

    An intelligent species of extraterrestrials might have telescopes far more powerful than ours.

    Scientists have been trying to discover planets around other stars for generations. They finally succeeded in the 1990s, and more than 4,000 have been catalogued since then.

    But could aliens have found our planet? Is Earth cataloged by even a single population of extraterrestrials? If so, what do they really know about terra firma?

    You may consider this an idle question, of no greater importance than asking if gerbils enjoy oboe concertos. But the answer is of real consequence for those who scan the skies for signals from intelligent aliens. After all, if extraterrestrials are unaware of our world and its properties, what would spur them to transmit signals in our direction?

    Additionally, if you’re among the many folks who are convinced that aliens are sailing through the troposphere, it might help your self-esteem to know that extraterrestrials could have learned enough about us to pay a visit.

    Full article here:


  • Ljk September 27, 2019, 19:36

    Video of James Bedford’s lecture on the subject of ETI Lurkers:


  • ljk October 6, 2019, 14:17

    Intelligent Ways to Search for Extraterrestrials

    Is there a more rational way to scan the heavens for alien life?

    By Adam Mann

    October 3, 2019

    Suppose you’re a space-faring alien society. You’ve established colonies on a few planets and moons in your solar system, but your population is growing and you’re running out of space. What should you do? Your brightest engineers might suggest a radical idea: they could disassemble a Jupiter-size planet and rearrange its mass into a cloud of orbiting platforms that encircles your sun. Your population would have ample living area on or inside the platforms; meanwhile, through solar power, you’d be able to capture every joule of energy radiating from your star.

    The laws of physics suggest no reason why this plan wouldn’t work; they merely require that all the energy collected be radiated out again as heat, lest the whole construction melt. This, in turn, means that your cloud of platforms should softly glow. A distant observer training a telescope on your solar system might see something like a hot, opaque screen encircling a dimmed star—a spherical entity, curiously bright at certain wavelengths.

    The theoretical physicist Freeman Dyson first speculated about the existence of such structures in 1960. In the decades since, astronomers on Earth have looked repeatedly for so-called Dyson spheres, and nobody has seen one. There are different ways of interpreting this result. Jason Wright, an astrophysicist at Pennsylvania State University, told me that Dyson wrote his original paper while contemplating an abstract idea—that “the fundamental limit to an energy supply that a species could have is all of the starlight in their system.” The fact that Dyson spheres haven’t been found, Wright said, doesn’t prove that aliens don’t exist. It might just mean that astronomers should start looking for evidence of less ambitious alien projects.

    Full article here:


  • ljk December 6, 2019, 10:43


    Will recent advances in AI result in a paradigm shift in Astrobiology and SETI?

    Joe Gale, Amri Wandel, Hugh Hill

    (Submitted on 19 Sep 2019)

    The steady advances in computer performance and in programming raise the concern that the ability of computers would overtake that of the human brain, an occurrence termed “the Singularity”.

    While comparing the size of the human brain and the advance in computer capacity, the Singularity has been estimated to occur within a few decades although the capacity of conventional computers may reach its limits in the near future.

    However, in the last few years, there have been rapid advances in Artificial Intelligence (AI). There are already programs that carry out pattern recognition and self-learning which, at least in limited fields such as chess and other games, are superior to the best human players. Furthermore, the quantum computing revolution, which is expected to vastly increase computer capacities, is already on our doorstep.

    It now seems inevitable that the Singularity will arrive within the foreseeable future. Biological life, on Earth and on extraterrestrial planets and their satellites, may continue as before, but humanity could be ‘replaced’ by computers. Older and more advanced intelligent life forms, possibly evolved elsewhere in the universe, may have passed their Singularity a long time ago.

    Post Singularity life would probably be based not on biochemical reactions but on electronics. Their communication may use effects such as quantum entanglement and be undetectable to us. This may explain the Fermi paradox or at least the “Big Silence” problem in SETI. [This idea is hardly new, but it’s nice to see the mainstream professional community finally starting to catch up with the concept.]

    Comments: 9 pages, 2 figures, accepted by International Journal of Astrobiology (in press)

    Subjects: Popular Physics (physics.pop-ph)

    Cite as: arXiv:1910.03944 [physics.pop-ph]
    (or arXiv:1910.03944v1 [physics.pop-ph] for this version)

    Submission history

    From: Amri Wandel [view email]

    [v1] Thu, 19 Sep 2019 17:20:37 UTC (926 KB)


  • ljk January 2, 2020, 13:51

    Why We Keep Sending Music to Extraterrestrials

    Music is an ideal medium for interstellar communication.


    JAN 02, 2020 at 5:45 AM


  • ljk January 28, 2020, 14:10

    Most of the history of SETI has been about trying to find aliens who are really just versions of us. Well, this ain’t Star Trek and so far we haven’t detected anything definite, so perhaps it is about time that we started thinking and searching outside the box:


  • ljk February 4, 2020, 23:33


    Lens Flare: Magnified X-Ray Binaries as Passive Beacons in SETI

    Brian C. Lacki

    (Submitted on 1 Feb 2020)

    Low mass X-ray binaries (LMXBs) containing neutron stars are both extremely luminous and compact, emitting up to ~10^6 L_sun within a kilometer-scale boundary layer. This combination allows for easy modulation, motivating X-ray SETI.

    When X-ray lenses smaller than planets (100 – 1,000 km) magnify the LMXB boundary layer, it brightens by a factor of several thousand for about a second.

    In addition, there should be occultation events where the neutron star is blocked out.

    Passive X-ray lenses could require little maintenance and the LMXB light source itself shines for millions of years, serving as an effective beacon for interstellar communication. A very large number of lenses would be needed to ensure detection from all directions, however, and gathering material to construct them could be very difficult. Avoiding collisions between lenses and aiming them pose additional challenges.

    Both “lens flares” and eclipses of LMXBs are easily detectable in the Galaxy, although they would be rare events, occurring once per decade. Our X-ray instruments could detect the flares to several Mpc, but it is unlikely they would be observing the LMXB during a flare.

    Comments: Submitted, 15 pages, 4 figures, 1 table. An animated version of Figure 3 is available at this http URL

    Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Popular Physics (physics.pop-ph)

    Cite as: arXiv:2002.00128 [astro-ph.HE]
    (or arXiv:2002.00128v1 [astro-ph.HE] for this version)

    Bibliographic data

    [Enable Bibex(What is Bibex?)]

    Submission history

    From: Brian Lacki [view email]

    [v1] Sat, 1 Feb 2020 02:20:37 UTC (1,716 KB)