Schelling Points – Page 2 – Penn State Graduate Course in SETI

What’s the Best Way to Reach You?

To follow up on the end of my last post, what if by optimizing for photon communication, we’re just making a giant planet-sized wheat triangle that’s primitive, quaint, and functionally useless because no ETI in their right mind uses wheat triangles anymore?

The readings for this week, especially Hippke’s 2017 paper about other information carriers for SETI, actually settled my mind on this score.

To skip to the punchline, Hippke finds that everything that we know of so far is inferior to photon transmission (specifically 1 nm X-rays, based on the argument in his previous paper), except perhaps physical artifacts (which might be preferable if you don’t care about speed). This is exciting, and puts my mind at ease about the wheat field thing.

He looks at the following methods, and generally finds the following flaws:

You will notice a lot of ???s in the Pros categories, and I think that’s interesting. Hippke does a good job of going through a lot of messaging options that seem ridiculous at face-value (and not excluding them for that), working out some actual physics behind them, and doesn’t jump onto being a proponent of any “new thing!”. I appreciate this.

The assumptions that he makes with regards to point-to-point communication are interesting. He assumes that more information transmitted is preferable to less, information arriving earlier is preferable to later, and more efficiency is preferable to less. He then discusses, at the very end of the paper, how the landscape would change if any of these assumptions were incorrect (which is very cool!), or incorrect and stacking.

I would like to point out that Hart’s sociological argument probably stops any of this assumption-fiddling from mattering too much. Just because one ETI actually doesn’t care how fast information arrives (Because they’re very long-lived? Because they’re post-biological?) doesn’t mean that another won’t. Just because one ETI is naturally incurious and doesn’t care about actually transmitting their entire “encyclopedia” (if you will), doesn’t mean that another is.

If anything, I think that the “more efficiency / less efficiency” might be the easiest one to break without running afoul of this sociological argument. If you have access to enough energy, you won’t care whether a big METI project takes 10^-100 or 10^-95 of your energy budget. And, with the assumption that virtually all ETIs should have been around for far longer than we are (and that they care about energy/resources in the first place!), they’ll all probably have a much larger energy budget, and might not care too much about efficiency. Just a thought!

OMG WHY IS SETI ALWAYS IN THE RADIO WHY HAVEN’T THEY THOUGHT TO DO SOMETHING ELSE… They did?

In Townes (1983), it is proposed that the commonly accepted view that SETI should operate in the microwave might not be as robust as it seems.

Before this paper, most searches were proposed to be performed in the microwave region, but other regions of the EM spectrum can be shown to be more valuable when other considerations and conditions are used. For example, IR may be better than the microwave region if one considers the use of photon counting instead of linear amplification.

We do not know what design parameters ETI considers important for METI, so we should be very cautious about limiting what frequencies we search for. The microwave region is good in that it can be searched in “right now” (in 1980s time).

Shorter wavelengths could also be better if the geometric directivity of their telescopes can be utilized.

The paper is notable for looking at previous assumptions in SETI and trying to remove ones that may be unnecessary or ill-motivated. I also appreciate that it stresses that we should not get too confident in our guesses for what frequency ETI will use.

The paper still has practical considerations which will always be dated. It does not do a deep dive into the physical upper limits of transmission. This is not strictly a problem, but we now have technology that far surpasses that of this time, so the arguments for search recommendations are now outdated.

X-Rays = Best Rays

This paper contains an argument for X-ray SETI. I will admit that I was skeptical when I read the abstract – after all, X-ray photons are much higher energy than radio photons and thus the typical logic of energy efficiency (of the transmitter) does not apply.

The paper speaks about the “streetlight effect” – an observational bias that causes you to “look where the light is good” aka. to search where it’s easiest (cheapest, already available data, good quality data given your technology, etc. etc. etc.). So, to try to preempt the gradual growing of our “streetlight” and cut to the chase, so to speak, the authors wanted to derive a physical optimum instead of just looking at the current technological “sweet spot”.

In this paper, the authors only considered photons, which is a choice that I’ll comment on at the end of this post.

They decide that a minimum wavelength for communication is probably about an atomic width; they adopt 1 nm as their order of magnitude value. The choice of this wavelength is dictated by how smooth we could possibly make a physical receiver surface.

The actual focusing of wavelengths of this scale is typically done with X-ray grazing mirrors that involve multiple mirrors in the design, but they are expensive to build. Because of this, the authors also discuss as-of-yet unknown alloys that could be used in a single mirror design and focusing with EM fields (not possible now, needs too much energy, but maybe in the future?).

The authors make the point that the advantage of X-rays is the amount of data that you can send and the tightness of the beam that you can create (both functions of the shorter wavelength). With a tighter beam, the pointings that you choose have to be proportionally more precise, even down to having to account for a planet’s position around a star.

Another benefit of the 1 nm wavelength choice is that it works at all distances, even when extinction is considered. Gamma rays are even better in this regard (they are barely extinct by anything), but they also would require instrument precisions that exceed the physical limitations described in the early part of the paper.

Finally, if you assume that each photon carries 1 bit of information, the authors find that you can get reasonable data rates in the megabit per second-year range, which would be sufficient for substantial communications. They propose searching for intentional communications in the existing Newton-XMM X-ray data. They note, however, that we have the technology to create pulses that are orders of magnitude shorter than we can detect with current technology, and that the time domain constraint might make us miss potential signals.

A Few Final Thoughts

“Ephemerides sharing is likely to be a small but significant component of all interstellar communications” – how best to share ephemerides in a general way, with the least assumptions possible (Schelling Points?) might be an interesting topic in CETI.
Choosing to look at only photons is a fair choice, but I can’t help but wonder if this is analogous to placing a physical constraint on the giant wheat triangle proposed by Gauss by setting it at an Earth diameter. It’s a physical limit for the method, but it means nothing if the method itself is (in hindsight) quaint/silly/outdated. Maybe photons will be a quaint/silly/outdated mode three centuries from now, and this is just a pointless thought experiment. I have a little bit more faith in EM communication than that, but it is something to consider.

Optimal Frequency According to Hippke

Although this seems like unfair criticism, I found this paper to be dense, boring, and unnecessarily long. Given that, this post will be drier and terser than my other posts (apologies to my big fans).

The authors try to find the optimal frequency for an ET civilization (or I suppose possibly even Earth) to communicate with for long distances. In particular, they look to maximize the data rate. While this is all well and good, and is an interesting thing to think about, I’m not going to bother going into their analysis or even their conclusions because I frankly find them to be useless. All of the analysis assumes Earth technology and Earth knowledge and Earth communication. It irks me. While these assumptions are fair to a degree for when you are designing a search (with current technology we could produce this signal and detect this signal, etc), I feel that expanding them into such a deep analysis is not fruitful. I feel there is merit into looking into most wavelengths, and since a lot of SETI will turn into parasite searches or hopefully get its own funding to do its thing, most wavelengths will be analyzed, especially if time stretches on for a while without a detection. So I don’t think this paper is very useful for SETI.

That being said, there is merit to this for mankind and our possibly inevitable expansion in the solar system and maybe beyond. If there is a specific wavelength that, with our knowledge and technology, works best for long distance travel in terms of data rate, then maybe we should keep this in mind as an alternative to radio (if it’s better). I’m not sure our technology is currently advanced enough to communicate with x-rays, but in the near future I wouldn’t be surprise if it becomes feasible.

Intelligence before humans??

Wright (2017) explains that that searches for ETI should include searches within the solar system. He argues that it is a good place to look (either for extant or extinct life), because it is near the only place we for sure know harbours life, Earth. He argues that life could have arisen on other bodies in the solar system (namely Venus, Mars, maybe the moon, the icy moons, and possibly asteroids or KBOs), and mentions that it is even possible that a prior species on Earth arose before humans that was intelligent.

I agree with many points in this paper. I believe that SETI should include solar system searches, especially because of the data we already have for many of the bodies. This links back to the argument by Davies and Wagner (2013) that SETI should be done not based on the possibility of discovery, but based on the time and effort the search would take. Solar system searches take remarkably less time since the objects are closer to us.

Wright points out that Venus could have been a good host of life before it lost all of its water and went runaway greenhouse. Unfortunately, Venus has such a young surface from its volcanic flows that any evidence older than a couple hundred million years would be completely erased, and any evidence prior would likely be erased too. Mars is a decent target since it was probably wet once and capable of hosting life before it lost almost all of its atmosphere, but weathering on its surface is decent and any artifacts would probably be covered by now. Other objects in the solar system and their associated datasets should be searched for technosignatures though.

That being said, there is a point in Wright’s paper that I very much disagree with, and that is the possibility of an intelligent species before humans. While I will grant that the fossil record is horrifically incomplete, one flaw I find in this suggestion is the need for oxygen. Our planet was very anoxic before about 500 million years ago, and the rise of life is highly correlated with rising oxygen levels. While any life could have been anoxic, most astrobiologists search for life that requires oxygen since it is the only life we know. Wright is calling for an analysis of ancient facies in search for technosignatures; I think this exceeds the “low cost” criteria, especially given that a successful search requires the assumption that any life inferred did not require oxygen. On top of that, although the fossil record is lacking, there is no indication of any line of evolution that was anoxic, nor evidence of a rise in intelligence that went extinct (unless we include intelligent dinosaurs?). This suggestion just seems fanciful to me; although it would be kind of neat, we have absolutely no reason at all to believe that such a species arose, no evidence of anything that could destroy such a species (except maybe KT?), and any intelligent life would need to be anoxic and would defy our current understanding of life.

The PITfall of SETI

When people consider intelligent life, they often picture humanity. Most would not contend the fact that humanity is the only intelligent species on Earth. However, have we exhausted the search for traces of ancient, intelligent species? That is to say, have we considered the possibility an intelligent species existed millions of years ago, on or near Earth, with comparable intelligence? Jason Wright notes the dearth of literature on “indigenous technological species” in his recent paper. He contemplates that a search for Solar System artifacts can serve as a vector to answer the perennial question of whether life exists elsewhere.

Wright begins by providing a history of the search for extraterrestrial intelligence (SETI). Conventional SETI prioritizes interstellar radio signals, waste heat, or other methods to find life in the form of extraterrestrial intelligence. Within our local neighborhood, the search is biologically driven, focusing on the search for microorganisms on moons or biochemical markers as proxies for life. Wright makes the case to search for artifacts within our Solar System. While the exact probabilities are unknown, Wright postulates it should be easier for the origin of any artifacts or technosignatures to “be local, [rather than] an extraterrestrial species crossed interstellar space and deposited [it] here”. Given this, he coins the phrase “prior indigenous technological species” to convey an ancient species dwelling in the Solar System. Such a species possessed high intelligence but has since become either extinct or left the Solar System.

Any artifacts from this species could remain here to inform us of their past and Wright argues there are various locations to search for these artifacts, even on Earth. Many may argue the post-Cambrian fossil record should remove all doubts of another intelligent species, particularly due to the existence of endocasts. However, it is impossible to unambiguously gauge intelligence and cognitive ability from the fossil record. Wright also mentions the “Earth is quite efficient, on cosmic timescales, at destroying evidence of technology on its surface”. Geologists do believe there is a technosphere which might leave impact on the fossil record. However, artifacts on billion year timescales would probably be destroyed by tectonic processes and, at best, one could probably detect unnatural isotopic ratios. There is also the question of magmatism on an early Earth-like planet. While the oldest crust is 4.4 billion years old, the early Earth suffered from magmatism. The modern continental crust, along with plate tectonics, would have emerged much later, potentially eradicating any traces of earlier intelligent life. Wright appears to favor searching in places with little surface restructuring (unlike Venus), such as Mars, and suggests the subsurface should be searched. Other areas of interest are old objects such as asteroids or Kuiper belt objects. Exactly what type of life would persist to leave artifacts is not mentioned and this warrants consideration given the climatic changes on Earth (and Mars/Venus).

Wright’s hypothesis could read as a script for a video game like Halo. The fact that his hypothesis can reflect science fiction (or a video game) does little to bolster a search. Furthermore, this paper is easily distorted, perhaps unfairly and to Wright’s distress, to make a claim that aliens existed in the past (see here, here, or here, for less low-brow articles see here or here). This concept of an indigenous technological species is as plausible as dragons or unicorns. There is no evidence against either mythical creature, but this has not fueled a search for them. To this blogger, it is not apparent how one searches for an artifact or technosignature. We assume it is something readily disentangled from nature, but we are limited by our anthropocentric machinations. It is unsettling to form argument where (i) the answer may be beyond recognition or (ii) a conclusion is that all evidence was simply destroyed. Furthermore, it appears that a non-detection can be rendered insignificant as one could always imagine a different condition for artifact preservation. If one’s hypothesis is not testable, then it does not merit scientific consideration.

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.

Could ETI be in the Solar System?

In Freitas (1983), the author does a deep dive into where we should look and what ETI objects we should look for in our Solar System.

The paper takes a series of interesting assumptions in order to start quantifying the search it eventually describes. From the beginning, all ETI objects are categorized into 3 categories. “(I) Objects intended to be found, (II) objects intended not to be found, and (III) objects for which detection by us is irrelevant or unimportant”. He argues that objects in classes I don’t exist because the alien technology is so advanced, if they wanted it to be found, it would be. I don’t really agree with this assertion as most all communication methods rely at least somewhat on the technology level of the receiving civilization. Unless they had probes looking for population centers and landing directly next to groups of people, there is no guarantee that we find anything, especially if we aren’t spending a lot of effort looking. He also argues that objects of class II are impossible to observe. I will accept that class II objects are not worth looking for as if they do exist, I could easily see them having some advanced stealth technology that makes them nearly impossible to detect (at least at our current tech level).

Once he decides that we are looking for “objects for which detection by us is irrelevant or unimportant”, he places these objects in geocentric or selenocentric (moon-centric) orbit, likely at the L4 or L5 Lagrange points, as they are the only stable ones. Then, it is decided that an optical ground resolution of <10 m “is required for unambiguous visual detection from orbit of intelligent activity on the surface of the Earth”. I have no idea how he came up with this number, but if we can see totally unambiguous evidence of intelligent meddling on Mar’s surface with only 50m/pixel, I don’t see why we need this resolution.

After these assumptions, he compares his proposal to other proposed search spaces in a reasonable fashion.

“Facing” Reality but Remaining Hopeful for Artifact SETI Within the Solar System: A Critical Analysis of the “Face on Mars”

Is it possible that a civilization could have existed on Mars long enough to monitor the development of the terrestrial species Homo sapiens, recognize its burgeoning intellect and future greatness, and so think to construct a replica of its face out of the geology of their world, all the while leaving no other evidence of their existence into the present era? Or alternatively, is it possible that the solar system has been visited by an extrasolar intelligence who studied the terrestrial biota remotely from the Martian surface for untold eons and thought to construct a human face on Mars, leaving no other traces? These are the kinds of solutions that one would have to invoke to explain the “Face on Mars” feature in the Cydonia region of Mars imaged by the Viking orbiter in 1976. In 1988, Carlotto performed an digital imagery analysis of this unusual feature in an attempt to preclude all unnatural explanations, which he at the end admits that he was unable to do. The complexity of these solutions brings to mind one of the truth assessment protocols utilized in science, the Occam’s Razor. If two competing theories to explain some natural phenomon are equally good, then the one that should be accepted is the one which makes less assumptions. While not universally applicable, it has historically and in many cases shown its effectiveness, as in, for example, the case of explaining the retrograde motions of heavenly bodies based on a heliocentric model rather than on a geocentric model with added epicycles. No, I think it is probably a lot easier to conclude that humans are exceptionally well-equipped with pattern recognition abilities, especially of the facial kind, and that we have anthropomorphically projected this face onto an otherwise completely natural geologic feature on the surface of Mars. In his 1995 book The Demon Haunted World, the astronomer Carl Sagan treated this exact possibility in a rather jocular manner:

“Occasionally, a vegetable or a pattern of wood grain or the hide of a cow resembles a human face. There was a celebrated eggplant that closely resembled Richard M. Nixon. What shall we deduce from this fact? Divine or extraterrestrial intervention? Republican meddling in eggplant genetics? No. We recognize that there are large numbers of eggplants in the world and that, given enough of them, sooner or later we’ll come upon one that looks like a human face, even a very particular human face.”

That is, there were and are a variety of other surface features on Mars and based on the stochastic nature of surface geomorphology it is plain to see that at least a few of them would have features that we would identify as potentially human. In fact, others have pointed out that there exists a multitude of other face-like features on Mars as well, but which did not, for unknown reasons, garner the same amount of attention and scrutiny as the one at Cydonia. The Cydonian face is probably just an example of human credulity and willingness to suspend traditional conventions in the domain of the apparently supernatural. Sagan further writes:

“There was an unfortunate dismissal of the feature by a project official as a trick of light and shadow, which prompted a later accusation that NASA was covering up the discovery of the millennium. A few engineers, computer specialists and others – some of them contract employees of NASA – worked on their own time digitally to enhance the image. Perhaps they hoped for stunning revelations. That’s permissible in science, even encouraged – as long as your standards of evidence are high. Some of them were fairly cautious and deserve to be commended for advancing the subject. Others were less restrained, deducing not only that the Face was a genuine, monumental sculpture of a human being, but claiming to find a city nearby with temples and fortifications. From spurious arguments, one writer announced that the monuments had a particular astronomical orientation – not now, though, but half a million years ago – from which it followed that the Cydonian wonders were erected in that remote epoch. But then how could the builders have been human? Half a million years ago, our
ancestors were busy mastering stone tools and fire. They did not have spaceships. . . Is the Face a remnant of a long-extinct human civilization? Were the builders originally from Earth or Mars? Could the Face have been sculpted by interstellar visitors stopping briefly on Mars? Was it left for us to discover? Might they also have come to Earth and initiated life here? Or at least human life? Were they, whoever they were, gods? Much fervent speculation is evoked.”

As is made clear by these ruminations, much conjecture and fanciful leaps of imagination must be invoked to explain the face when venturing outside of the mundane and routine. It was later shown in a subsequent orbital mission to Mars in 2001 that the Cydonian face had substantially eroded due to surface weathering and presently hardly resembles anything human. This paper is important because although it is a demonstration of our weakness and failure to remain steadfastly objective in the face (pun intended) of something of potentially grave importance, it does also show that our knowledge of the surfaces of solar system bodies is not exhaustive. We don’t know whether there could actually be an object in the solar system for whom the most plausible explanation is extraterrestrial in origin. Therefore, there is a place for SETI even within missions to bodies in our own solar system to establish conclusively whether or not our solar system has been visited by an extraterrestrial probe or emissary.

Don’t Talk to Me About a Face on Mars

I couldn’t decide which paper to discuss this week, so I’m talking about both. One made me think, the other made me angry. I suspect that this was the intent of the assignment.

Solar system artifact SETI might be one of the most giggle-inducing subsets of SETI. This seemingly wasn’t always true (throwback to the Martian “canals”), but it suffers from a series of issues. One is that there is a popular misconception that the solar system is a relatively well-explored piece of “territory” and we haven’t found anything yet. So solar system artifact SETI, in that light, seems antiquated. It always surprises me to learn how little we know as I progress through my education, and I think that feeling is relevant here. In addition, solar system artifact SETI makes SETI seem so close to home that the only conceptual guideposts people have are (generally cheesy and terrible) science fiction. Where a remote detection or a long timescale exchange of radio signals would be distant, sterile, and narratively boring, the discovery of an alien probe in the solar system or a city and giant face on Mars feels like fiction, so it’s treated as such, instead of legitimate science.

Now, to the articles!

The Freitas paper very logically stepped through the process of finding an answer to the question “which surveys on which parts of parameter space would have to be performed to disprove the existence of probes in the solar system?”. I take issue to a couple of framing assumptions that Freitas makes. Firstly, I don’t think it’s reasonable to assume that any probes we would find would be made for a neutral-to-discovery purpose (because we would’ve found one already if it wanted to contact us and we’d never see it if it was trying to hide, the logic goes). I can imagine many exceptions to this idea: a probe that was meant for communication but was damaged, a probe that is trying its best to contact us but by a method that we don’t have access to yet (perhaps on purpose, so we only see it at a reasonable point in our technological development), or a probe that was only partly for communication (mostly for another purpose, with only minor energy put into a beacon). The other thing that bothered me is that all of the constraints for the observational probe were constructed under the assumption that the probe wanted to observe Earth. That looking at a habitable planet, and that having the resolution to watch civilization arise on it, were valuable to our hypothetical watchers. I think that’s a bit anthropocentric – it could very well be that our asteroid belt is absolutely fascinating and ugh look at the primitives mucking up that third planet, they’re everywhere in this sector.

All of that said: you can’t do this work without making some assumptions to reduce the scale of the problem, and these were relatively minor ones. I loved the structure of the paper: consider the construction and purpose of the probe, then consider where it could be placed, note previously completed searches and their incompleteness (chock-full of references), then look at detection probabilities with current instruments and reasonable times. This is a methodical and scientific way to go about the stated problem in the paper.

The Carlotto paper, on the other hand, was rage-inducing. It would take a very, very convincing landscape artifact for me to feel comfortable announcing a “non-natural” origin. If Europa was covered in a giant swastika a la Armada (Ernest Cline’s less successful follow-up novel to Ready Player One), that would probably be sufficient. The 3D face is reconstructed from only two relatively low-resolution images, which makes me uncomfortable. The feature has since been imaged from other angles (by, among others, the Mars Global Surveyor) and, spoiler alert, doesn’t actually look like a face.

This is an example of textbook pareidolia: humans have a tendency to see patterns in random data, especially and specifically faces. Being good at recognizing and reading faces is vital for a social creature like a human being, so better to have some false positives than to accidentally mistake one’s significant other for a coat rack. But a base and known brain-stem bias like this should NOT cause us to write horribly misleading papers about the possible existence of an extinct Martian civilization. I don’t know how couth it is to consider the political ramifications of other people’s research, but it’s frustrating to see a vibrant and important sub-field continually shooting itself in the foot with scientifically sketchy bold claims and over-speculation from a few members of the community.

/endrant