How to look for something that isn’t there

A common artifact searched for in looking for ETI is Dyson spheres, or some other megastructure whose purpose is to collect energy from the star. This structure was first suggested by Dyson 1961, but later expanded on by Kardashev 1964. Kardashev suggested that civilizations could be categorized into three different types, depending on the quantity of resources collected: a type I civilization would gather resources from their planet, type II from their star, and type III from their galaxy. Kardashev 1964, and later Annis 1999, and even later (sort of) Villaroel et al. 2016 argued that these different stages of civilizations could potentially be discovered! If a civilization were to harvest all of the energy from their star, then we would no longer see them (in the visible; the heat would dissipate as IR, leading to searches for this waste heat).

Villaroel et al. looked for disappearing stars. They compared data from Sloan and from archived data, looking for sources that were present in the latter but no longer there for the former. In essence, looking for disappearing stars. In the end, they found one potential candidate.

I said earlier that they sort of argued that this was a method for detecting other civilizations. I say “sort of” because they didn’t directly mention it. The thought is there, that this is a way to look for ETI, but the reasoning behind why ETI would cause a star to disappear is not mentioned. I’m sure there are a number of explanations that sci-fi fanatics could list, and maybe the authors did not want to potentially embarrass themselves by playing sci-fi author? Nonetheless, I’m not really sure, short of a Dyson swarm, what would cause a star to vanish. Feeding it to a BH?

That being said, I am becoming a fan of “parasitic” SETI searches. There is something about only needing to pay for time (not receivers or data) that really seems great to me! The data are already there, so why not go for it?

Reaction to Howard et al 2004

Continuing with the theme of optical SETI from last week, this week’s Howard et al (2004) paper discussed the results of an optical SETI experiment which searched for pulsed beacons around thousands of stars. Following with the other optical SETI papers we have encountered, the authors compare the merits of searches in the optical/NIR with searches for microwave/radio signals. If one’s figure of merit for the efficiency of technique is the signal-to-noise achieved for a fixed transmitter power, then optical methods are comparable to those of radio.

They further motivated this search by presenting the “Fundamental Theorem of Optical SETI”, which is a statement of the observation that even at our early stage of technology (Earth “2000”), we can already generate artificial optical pulses could appear to outshine the brightness of the Sun by a factor of 10^4. This follows a similar line of reasoning as the Schwarz & Townes paper from last time, which plausibly suggested that some ETIs would rapidly discover some form of optical interstellar communication and use it. However, in the case of Howard’s paper, the focus is on the search for pulsed beacons, which are unambiguous detections of alien laser signals (for which there are no possible astrophysical confounders or dopplegangers).

With similar avalanche photometer instruments at Harvard and Princeton, they began their campaign which would eventually consist of some 16,000 observations totalling 2400 hours of observing time spread over a five year baseline. They searched 6176 stars in their survey, of which only a handful of signals showed any promise as plausible artificial pulses (most were explained away as being stochastic in nature). Three triggers from HD 220077 were considered the most interesting, and were allotted many follow-up observations. Upon further investigation of those candidates, they found that their photon rate was consisten with Poisson noise and thus rule out the alien hypothesis. (Remember, it’s never aliens!) Another interesting pair of triggers from HIP 107395 was considered too ambiguous because of an asynchronicity between the Princeton and Harvard clocks.
This work was performed in fulfillment of Howard’s PhD thesis in astronomy; Andrew Howard is now a prominent exoplanetologist and astronomer, and so this work is a demonstration of SETI being firmly rooted as a part of astronomy and an example of the quality that SETI papers ought to strive for (that is, when it is taken seriously by astronomers and other scientists). It is also a good example of “Forensic” SETI done right, where the candidates were scrutinized on a case-by-case basis and all natural explanations were attempted to be exhausted before jumping to unsubstantiated conclusions (which contrasts with the approach of some other papers we have read this semester *cough* faces on Mars *cough*). Although the results were null, the study still placed valuable upper limits on the occurrence of beacons around nearby stars. Therefore, this paper serves as a template for how null results ought to be reported and makes a case for them to be published.

Now, I Will Make This Star… Disappear!

Villarroel, Imaz, and Bergstedt 2016 had an interesting theory that they actually tested. Regardless of your opinion of the theory, you have to respect them for actually performing their search, which is something that too few SETI papers do.

They wanted to look and see if any objects have disappeared from the sky and slipped under the radar. The methodology was pretty straightforward: they looked at the US Naval Observatory sky catalog and found objects with low proper motions. Then they created four parent catalogs (with differing criteria like “needs >4 detections” or “needs to be < 18 mag”). They look for and exclude corresponding objects (by position) in SDSS data, which cuts out a lot of their objects. Many of the remaining objects actually are still present in the SDSS data but were just missed by the pipeline – they looked at these images by eye for this reason. Examining by eye also allowed the removal of any artifacts that were causing the difference in detection. After this cut, 148 objects remained. Many of those don’t even have a visible object in the USNO catalog, suggesting that there were errors in their proper motions / positions or were just noise from the beginning. After all of this, only a single candidate remains, shown below.

I personally am not convinced about the existence of this object in the first place. I believe that the authors are talking about the spot in the middle of the “triangle” of objects almost directly in the center of the image… but honestly, I could easily see it just being noise. I don’t know that I would suggest that it was “clearly seen”.

So, now that I’ve gone through the paper itself, why did the authors think that looking for a disappearing object would be an interesting or sensible thing to do, and why might it relate to SETI? The building of a Dyson sphere was suggested as a way to make a star disappear, but I don’t believe that the authors’ timescale (60-70 years) is feasible by even Dyson’s original calculation based on the energy needed to construct it vs. the energy output of the central star. Mostly, a disappearing star or galaxy would be something that we would not expect nature to do, so it’s either interesting SETI or interesting astrophysics (high risk, high reward, high turns-all-of-astro-on-its-head factor). If the action causing the “nature-plus” effect is ETI but not intentional communication, then the philosophy behind this search is the equivalent of searching for the most “obviously artificial” technosignatures possible, which is one way to approach the haystack.

Personally, I like the idea of this search, following Paul Davies suggestion in his lunar artifacts paper – it’s quite simple to make sure no objects have disappeared from the sky in the last few decades. Like, they probably haven’t, but it’s a good thing to check on.

Final Point: The discovery of a disappearing galaxy would be terrifying, whether ETI or not. I honestly don’t know how I would react to that. Probably with the same or greater instinctual fear as I would have towards beings who think it’s fun to send messages in gravitational waves. Maybe some curiosity, but curiosity requires a hope of understanding. A disappearing galaxy would require power/energy so far beyond our comprehension that the result is basically god-like (one is reminded of Q from Star Trek, although he mostly just spent his time trolling Picard, so perhaps that’s a bad example). At any rate, I’m kind of glad that they didn’t find any of those.

A Way to Find Big ETI Laser Pointers

In Wright et al. (2014), a new, versatile optical SETI instrument is described that can search for direct evidence of interstellar communications via pulsed near-infrared signals. The article is in an SPIE (Society of Photo-Optical Instrumentation Engineers) conference proceedings paper and focuses heavily on the physical design of the detector and optics.

Modern high-powered lasers can easily outshine our Sun (for limited frequency ranges and times). As such, it is obvious that, if advanced ETI exists and wanted to communicate (or just broadcast its presence) specifically with us, it could easily do so with lasers. According to the article, the largest lasers on Earth are detectable with meter-class telescopes up to thousands of light years away. This is because, unlike radio signals, optical beams can be finely focused, providing a high received power flux for each amount of transmission energy.

Fast NIR pulses searches are an underexplored area not just for SETI, but for astronomy in general. Astrophysically-based nanosecond optical pulses are supposedly very rare, but this instrument is also planned to observed possible pulse sources such as pulsars, black holes, cataclysmic variables, gamma-ray bursters and active galactic nuclei.

The instrument works by utilizing commercial-off-the-shelf (COTS) products including NIR photon counters that, for the first time, can be very fast, wide bandwidth, high-gain, low noise and cheap. The light from the sky comes in and the NIR light gets split into two independent detectors (to help eliminate false positive detections) while the optical light goes to a guide camera so that they know that the telescope is pointed at the right place. Their setup is capable of recording the time of arrival of signals down to the nanosecond and it is planned to be used on the 1-meter Nickel telescope at Lick Observatory in California.

The Dangers of Sensationalism

I am very critical of yellow journalism, especially when it comes to the topic of the burgeoning search for extraterrestrial intelligence. It seems that in order to draw more traffic to their domains, journalists are often incentivized to throw in more buzzwords or sensational misrepresentations of the primary message of their interviewees. In this department, Andersen’s article in The Atlantic fares moderately well in that he does not go headlong into sensation (though he does participate to some degree, as we shall see). The article provides decent exposition on the astronomical techniques used in the detection of exoplanets and an account of the events regarding Tabby’s star as they unfolded. My primary qualm with the presentation was that they emboldened and enlarged a paraphrase of a quote from Prof. Jason Wright, which seemed to distract from his main message (My secondary qualm is that in their last sentence they suggeste that Tabby’s star might see Earth transit, but the declination of Kepler field stars places them well beyond the range of the Earth transit zone). In the paragraph text, he says: “Aliens should always be the very last hypothesis you consider.” This is what most certainly, if any, should have been emboldened and enlarged. Instead they chose: “… it looked like [something] you might expect an alien civilization to build.” To the lay person who might only read the article in brief and without skeptically-trained eyes, they may come across this latter phrase and then go on to tell all their friends and family a false truth regarding Tabby’s Star due to this choice of emphasis. This is obviously dangerous to the representation of SETI and astronomy in general, and may tarnish the reputation of the field and the authors consulted. I would strongly admonish any deviation from a purely accurate representation of the ideas and phrases of a scientist, especially so in this area. Therefore, it is the role of the scientist to effectively explain the subtlety of their position to the journalist and the role of the journalist to reflect such a position with fidelity in the popular article.

Cost vs. Plausibility, Stingrays, and Lunar Spelunking

The approach of Davies and Wagner (2013) is a good one as far as SETI papers go, so I’ll start with a quick summary of the salient points.

The primary point of the paper is that a search of data from the Lunar Reconnaissance Orbiter should be performed, looking for anything out-of-place that indicates the presence of non-terrestrial artifacts (or NTAs, to borrow a phrase from Haqq-Misra and Kopparapu (2012)) or past non-terrestrial activity. The authors argue that the moon is a good place to search for artifacts for many reasons: it’s close and we have good, high-resolution data of it, the surface is unchanging (on a hundreds of millions of year timescale), and it’s tectonically inactive, so we don’t have to worry about the artifact’s signature being swamped by thermal/radioactive/magnetic processes from geological action (like we would have on the Earth).

Look at this cute lil’ orbiter

The authors then divide potential NTAs into four classes, based on assumptions that they openly admit are anthropocentric (which is refreshing, compared to some of the other papers we’ve read).

The first class is messages, things that are “deliberate” in catching our attention. One thing to keep in mind is how long the message might have been waiting there – the longer it needs to last, the harder it will be for us to find due to the trade-off of detectability and durability.

The second class is scientific instruments, which have a nice symmetric pro and con. Con: they wouldn’t’ve been made for us to find, so they may not be easy to spot or recognize. Pro: instruments need power supplies, and power supplies are more easily detectable (think solar panels or waste heat).

The third class is trash – things left over from prior expeditions and never cleared away – a category that humans are particularly good at. The authors make a case for searching in lava tubes – trash left there would be protected from asteroid impacts and could lay undisturbed for far longer than something on the surface. I’ll be the first to admit that lunar spelunking for alien artifacts sounds like the most epic job posting ever, but it probably isn’t realistic to expect that a search like that would occur any time soon, even if we had any reason to believe it would be successful.

The final class of NTA is “geo-engineering”, or scars on the moon’s surface left behind by some prior alien activity (mining? excavations? who knows). Features created by geo-engineering might be easier to spot with the data based on scale, but the difficulties come in trying to decide which features are natural vs. NTAs, and which features are even interesting in the first place.

At the end of the paper, having defined some idea of what we might be looking for, the authors give some examples of ways to search the already extant LRO photographic dataset for these features. I decided to organize and expand on their suggestions in the following table:

This table is specifically in reference to the problem of searching for NTAs in LRO photographs, but it could be easily generalized to any big-data SETI project, and even many big-data projects in general. I think this is a useful summary for thinking about the problem of big-data, and a good argument for why the multiple-pronged approach that was being tried by the authors is the way to go.

{Side note: I am a huge proponent for citizen science as a way to make scientific progress while educating and engaging the public. I participated in many citizen science projects in middle and high school, and led a Seafloor Explorer competition for 20 middle school students that classified the objects and wildlife in ~10,000 images of the Atlantic seafloor. The gallery below shows some of the images that my students got very excited about in the classifying process. Applying a citizen science strategy to SETI could be very useful…}

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To end this post, I’m going to change gears and get a little philosophical for a moment. The authors make an interesting case for pursuing SETI in large, already existing databases – many SETI ideas are low cost and high potential reward projects and should be pursued based on cost over plausibility. I still don’t entirely know how I feel about that idea. Could that mentality be politically destructive for SETI in the current funding landscape, and should that matter if science is being done and progress is being made? Does it lend legitimacy to fringe-sounding ideas, like the genomic SETI concept that the authors mention (ex. this paper), or does spending a little bit of effort to test and debunk these ideas actually make the field better in the long run? Are we uncertain enough about the nature of ETI that disregarding plausibility and just prioritizing by cost is actually a more logically consistent way to go about the search?

I don’t have answers, but I think these are interesting questions and we should keep mulling over them.


Scrapyard SETI (Get an Undergrad to Do It)

In Davies & Wagner (2013), the authors describe and motivate an ongoing (circa 2013) search of Lunar Reconnaissance Orbiter imagery for unusual features at the LRO Laboratory at Arizona State University.

The first point of note that I found in the paper was the initial statement of assumptions. They state that anything we could find (outside of communication SETI) will most likely be something “post-biological” due to the long timescales we would have expected it to last. Then they directly state that we have no reasonable way to extrapolate our own technology to guess what type of artifacts we should be looking for. An openness I found refreshing.

What follows is an intriguing and frank basis of motivation for the search of the LRO database (or any database). In the case that we don’t know what we are looking for, they propose that the best way to make meaningful progress with limited resources is to simply search all existing databases for “artificiality” and that choosing which databases to search should be tied only to cost rather than the likelihood of results. This was an interesting thought. Cost is obviously a good thing to keep in mind when deciding on what to do with resources, but in every other field, missions and grants are proposed and evaluated with heavy basis placed on their merit. But what is it is nearly impossible to quantify the merit of an experiment?  We can estimate the number of planets TESS will find (>20,000) or the amount of stars GAIA will get parallax for (>1 billion), but there’s no way for us to know the amount of ETI signatures will be found by performing any given search (although, one could cheekily say 0 based on the results of all other searches). While this seems to make sense at first glance, I think it makes some false equivalencies. Just because we don’t know the utility of two different searches does not mean their utility is equal, as this line of thinking implies. If cost is the only thing that matters, I should just submit two half-cost proposals that each cover half of a database. That’s two half-cost searches for the price of one! In the same vein, some databases are clearly more valuable to search than others. Imagine two equivalent cameras take pictures of the Martian surface, the only difference being one of the cameras can take pictures of much higher resolution. It is clear that while it would be more expensive, looking at the higher resolution data would be much more useful. While it is difficult to quantify the utility of SETI searches, they can be viewed as setting limits on the parameter space (a la Jill Tarter’s Needle In A Cosmic Haystack) that SETI artifacts can inhabit (see Appendix A Wright & Oman-Reagan (2017) for a motivation of this type of quantification).

Besides these points, the authors discuss how automation is ill-suited towards artifact SETI as we have to program in exactly what signatures we want to look for. Currently, they have some students and faculty searching the Narrow Angle Camera images for interesting features by eye. They suggest that the best strategy may be to utilize the time of enthusiastic volunteers to perform the image analysis.

Searching for Monoliths: When Science Fiction Informs Science Reality

In 1999, American satellites in orbit around the moon detected a strange magnetic anomaly emanating from within the crater designated Tycho. An early explanation for origin of the anomaly source was a ferrous meteorite, but that could not account for the strength of the produced magnetic field. A few years later in 2001, an expedition to the anomaly site was dispatched from the lunar base at Clavius. The team was led by astrophysicist and former chair of the US National Council of Astronautics, Dr. Heywood Floyd. The expedition revealed a structure, in more ways than one similar to a black box, with rectangular prismatic dimensions in the ratio of the squares of the first three nonzero natural numbers. This ratio held even when the distances were measured at the finest resolution afforded by modern instruments. Subsequent radioisotopic dating of the surrounding regolith implied that the structure had remained in place for some three million years, long before any lunar activity attributable to any human nation and in fact older than the genus \textit{Homo} itself. Given its age and unnatural design, scientists were led to conclude that the object is not of this world nor of this solar system, but actually an emissary of some advanced extraterrestrial civilization sent to monitor the development of the human race.

Does it sound like science fiction? The above story is indeed fictional and is actually lifted from the plot of 2001: A Space Odyssey, a film and novel by Stanley Kubrick and Arthur C. Clarke (which itself is influenced by Clarke’s earlier short story The Sentinel). However, this is fundamentally the type of object that SETI scientists are now seriously contemplating searching for! (As such, we should be mindful of the great ideas that have come to us from science fiction.) Setting aside great storytelling, one of the core ideas of this film was that the Earth had been visited in the remote past by an alien intelligence who established and left behind artifacts after their survey of the solar system was complete. Whether the artifacts were left deliberately or otherwise inadvertently is less important as is the fundamental question of whether or not it is possible for us to perform an exhaustive search for them. In 2013 (nonfiction timeline), Davies & Wagner suggested exactly this kind of search and also overviewed the kinds of strategies we might use to detect a variety of signatures which would suggest that the Moon had been visited in the remote past. These strategies revolve around searching through the Lunar Reconnaissance Orbiter (LRO) data, which offers high resolution imaging of the lunar surface. In this way, SETI science can “piggyback” off the gains of traditional science, which often acquires data that can dually be utilized for SETI purposes. (Imagine the difficulty of justifying a complete surface map of the Moon for the explicit purpose of searching for alien artifacts in a mission proposal to NASA!) With the LRO data, we are afforded the ability to search for 1-10m class objects which could be the detritus, message-carrier structures, habitats, or instruments of a past alien visitation.

This paper is the logical continuation of the Bracewell 1960 paper applied to the specific case of stationary (possibly perpetually ensconced by craters or more likely subterranean) artifacts on or near the surface of solar system bodies. (The original paper did not deal with this case, but focused more on probes in orbit, which was later expounded upon by Freitas 1983.) In my reaction to Bracewell, I suggested how a search for exposed artifacts on the surface of solar system bodies could be a feasible project given modern artificial item recognition software and machine learning algorithms. However, as the authors point out, there are difficulties with the lifetimes of exposed structures given that any region on the surface of the Moon, for example, is likely to be struck by impactors on vast geological timescales, releasing energies which no known materials would be immune to. This problem arises since the progenitor civilization is expected to be truly primordial given the expanses of cosmic time, and hence their probe is likely to be millions or possibly even billions of years old. Therefore, the artifacts would probably be buried and a subsurface search conducted with penetrating radar or by a human expedition is motivated for the future. For the present however, we are limited to “relatively” recently deposited surface objects which could have been picked up in the LRO survey maps. To process this vast amount of data presents another issue, since although it could be processed without automation, it would probably require tens of thousands of man-hours to sift through it all. The cost and upkeep of such an effort would obviously defeat the purpose of a low-cost, low-effort SETI search. In the case of automation however, machine learning algorithms are limited to identifying only those objects on which it is trained to identify. For example, a machine may be exquisitely capable of identifying particular geometrical shapes, but who is to say that an artifact need be perfectly geometrical? And what of partial or nearly complete obscuration by lunar regolith built up over time? The corner of a cubical object protruding from the ground would be missed by a machine trained to search for cubes. These many difficulties make the whole idea altogether less appealing. Until a general purpose artificial intelligence or serious effort of crowd-sourced volunteers can be employed on such a task, the completeness of the search will remain low. This should not be upsetting though, because as long as the search is incomplete there is still some chance for a positive detection. Who can say, perhaps Clarke and Kubrick will be vindicated some time within this century! (As a humorous aside, it was recounted by Clarke how the astronauts of Apollo 8 were tempted to radio back that they had seen an enigmatic black structure on the surface from orbit, but they decided that it would be in poor taste.)  Nonetheless, it is clear that the search is on for evidence of alien artifacts within the solar system, a search that is certainly nowhere near over.

The Mock Side of the Moon

If extraterrestrial intelligence has visited the moon, there may be signs of their activities. Or, at least, astrophysicist Paul Davies and his student Robert Wagner seem to think so. In a paper published in Acta Astronautica, Davies and Wagner argue that scrutinizing the surface of the moon for extraterrestrial artifacts may prove beneficial in the search for extraterrestrial intelligence (SETI). They argue this can be archived with the data from NASA’s Lunar Reconnaissance Orbiter (LRO). The mission of the LRO is to serve as a lunar mapping program to flag potential landing sites and characterize the radiation environment, among other things. LRO has the capability to obtain photographs of the lunar surface up to 50 centimeters per pixel using the Narrow Angle Camera (NAC, see Figure 1). The high resolution is required to provide the greatest sensitivity for a correct detect, and mitigate cases like the Martian face. Davies and Wagner believe the hundreds of thousands of photographs provided by NAC can be capitalized for SETI, much like IRAS and WISE have been.

Figure 1: Two LRO images from 2009 (early mission image) and 2011 showing signs of human activity on the moon and the need for high resolution images! Davies and Wagner propose to look at the entirety of images captured by LRO to search for extraterrestrial remnants on the moon. It is easy to detect these surface features as we know where and what to look for. The search for unnatural features on the moon would require extensive human effort or automation of some sort. The images do not line up perfectly because of differences in lighting conditions, angle of the LRO Camera, and other variables. Image brightness and contrast have been altered to highlight surface details. Source: NASA’s Goddard Space Flight Center/ASU

To further bolster their claim, the authors contemplate the types of extraterrestrial artifacts (ETAs) that would persist through the regolith on the lunar surface. They largely consider four classes of artifacts:

  1. Messages, or artifacts designed to be found and interpreted by an intelligent species,
  2. scientific instruments, or observational devices sent across interstellar space (e.g. probes) or remnants of an alien expedition to the moon with potential functionality,
  3. trash, or objects left behind by alien expeditions without any regards to its survival (e.g. radioactive waste, spacecraft remnants), and
  4. geo-engineering structures, or changes to the moon due to alien activities (e.g. mining or construction).

The most attractive scenario for Davies and Wagner would be for aliens to have left a message a few million years ago. They argue anything older than this would be buried on the moon or have been destroyed by meteoric impacts. Such a message could be near an existing landmark on the moon or have a “radio beacon”. On the case of scientific instrument, the search would most likely favor a search for electromagnetic emissions as opposed to a photographic search. The authors note they have searched the poles for signs of “alien solar arrays” and nothing has been identified yet. Robust searches for extraterrestrial trash or geo-engineering would require something other than photography. However, Davies and Wagner argue potential searches include near lava tubes (for trash) and for artificial topographic features (e.g. open-cast mine). Perhaps the most important outcome is the extent of the search. While only 25% of the lunar surface was imaged at the time, the authors have only been able to automate the search for simple pits. They emphasize the need for crowd-sourcing and citizen science (like the now defunct Moon Zoo) in this endeavor as we do not know a priori what to look for.

Movie 1: The moon has been able to keep its secrets until now! Dexter makes an odd observation about the moon (it’s been geo-engineered into a Martian base) and goes to find out what is causing it. He discovers Martians on the moon in a sub-lunar city planning to attack Earth – essentially SETI/SETA in a nut shell as anything is possible with enough imagination. Davies and Wagner propose LRO observe the lunar surface, but for all we know there could interesting things beneath the surface. Source: Dexter’s Laboratory, Cartoon Network/Hanna-Barbera.

While it is a benign project, the premise belongs in science fiction. Davies and Wagner present a very anthropocentric view on ETAs, going so far as to consider “a simple capsule … with a … splash of paint” and “round, open-cast mine[s]” to argue for some of their unorthodox targets. It would appear they want to search for human-like aliens. If we ascribe such human features to them, then perhaps we should consider other searches for them (see Table 1). Freitas Jr. has presented a new approach to SETI in searching for probes that includes the moon and other parts of our Solar System. With all this talk of ETA, this blogger is reminded of a cartoon (see Movie 1) where the strange observations of the moon led to the discovery of a sub-lunar city of Martians. It seems so outlandish, but if we are using our imagination to guess aliens are or have been on the Moon, why stop at the surface? If we consider aliens that are so advanced as to have explored the moon, why should anything they leave be obvious to us on the surface? As with SETI, the lack of data is a problem and makes this search worth a modicum of effort, however tepid and benign the results may be.

Table 1. Cost-Effectiveness Hierarchy of SETI Objective (from Interstellar probes – A new approach to SETI, Robert A. Freitas Jr.)
Estimated Cost
SETI Search Method To Be Employed
Small -instrument visual/photometric artifact searches of Earth-Moon libration orbits to mag. +18
Infrared search for “warm” artifacts (T ³ 50 K) in Earth-Moon libration and solar polar orbits
Radar search for small artifacts in Earth-Moon libration and solar polar orbits (Goldstone, Arecibo)
Continuing ad hoc beacon searches at various radio frequencies, employing as many new and different search procedures as can be devised
Large-instrument artifact search of Earth-Moon libration and solar polar orbits to mag. +25
Large-instrument ecliptic survey to mag. +20/+25, looking for evidence of incoming fusion braking rockets, solar sails, interstellar ramjet plumes, laser pushbeam backlighting, or relic corner reflectors
Proposed NASA Ames/JPL extrasolar radio beacon survey to 100-1000 light-years, using 109 channel MCSA at waterhole frequencies
Beam call signals toward Earth-Moon, Earth-Sol, and Jupiter-Sol libration orbits, and solar polar orbits, using waterhole and other appropriate SETI frequencies
Unmanned photographic/sampler probe to Earth-Moon libration orbits. looking for ET artifacts
Unmanned photographic/sampler probe to Earth-Sol libration points, looking for ET artifacts
Unmanned lunar orbiter/lander, surface mapping and artifact search
Unmanned photographic/sampler probe to Jupiter Sol libration points, looking for ET artifacts
Extended MCSA radio beacon surveys to 1000 light years, across 1-100 GHz
Unmanned mobile Mars lander and orbiter/lander to Martian moons, surface mapping and artifact search
Unmanned mobile lander/orbiter to inner planet, outer planets and moons, surface mapping and artifact search
Manned exploration of Earth’s Moon, surface mapping and artifact search
Full ground-based Cyclops/Orbital Cyclops/”Lunarcibo” radio beacon search to high sensitivity out to 1000-10,000 light-years
Full ground-based Cyclops/Orbital Cyclops/”Lunarcibo” eavesdropping search to high sensitivity out to 10,000 light- years for Type I civilizations, intergalactic range for Type II civilizations
Unmanned mobile lander/orbiter probes to Asteroid Belt, surface mapping and artifact searches
Manned exploration Of Mars and Martian moons
Manned exploration of inner, planets, outer planets and moons
Manned exploration of the Asteroid Belt

SETI can be cheap; let’s do it

This post won’t really include much about Davies & Wagner 2013, expect for one line:

“[T]he criteria for searching a database should be primarily tied to cost rather than plausibility. If it costs little to scan data for signs of intelligent manipulation, little is lost in doing so, even though the probability of detecting alien technology at work may be exceedingly low.”

This is remarkably well said, and I completely agree. A huge argument against SETI is that nothing has been found yet, so it’s a waste to keep looking. While this argument is fallacious in itself, it can quite easily be rebutted with the above statement. If searching requires little time/money/effort, than there is no waste.

One great thing about SETI is that it (normally) does not require its own dataset. Astronomers are already observing interesting targets with different instruments at different wavelengths, either to catalog them or to look for anomalies. Any anomalies discovered will probably be scrutinized, so why not borrow the data and look at it from a SETI point of view? There are currently many algorithms searching datasets now (a solution to our big data problems), so altering these algorithms just slightly to look for expected ETI alterations or just anomalies takes minimal effort and, if the algorithm is light, has minimal computation costs. Such searches could even just piggyback off of current searches (flag anomalies) such that there is no additional computational costs.

Davies and Wagner specifically motivate looking through all of the wonderful data we have on the Moon, noting that because the resolution is so great, many artifacts/trash would be visible (assuming they aren’t buried in regolith). Personally I think that looking at these by eye is not the way to go, and that the search should be automated. It would also be neat if some machine learning were applied to find such artifacts, but this would require some kind of training set and therefore not only more work/time/money but also some kind of assumptions about the sizes and shapes of alien artifacts.

I think it would be really neat if someone were to dedicate some time (probably unpaid =/) to developing algorithms for finding anomalies in all of the (mostly planetary) datasets we have (images, transits, gravity anomalies, all-sky surveys in every wavelength). This would not take much, and the algorithms could just run in the background. Follow-ups for any flagged anomalies would include compilation of all possible data and either human or artificial analysis to somehow rank how anomalous the data are. This would simply be really awesome.