In Lin et al. (2014), an interesting possibility of using biosignature detection to infer the presence of not just life, but intelligent life, is explored.
One way you can infer the presence of life on a planet is to look at the atmospheric ratios between compounds, elements, or isotopes in an atmosphere and find that they are out of equilibrium. For example, if you found molecular oxygen in combination with a reducing gas, there would be a readily available way for life to generate energy by harnessing the changing energy by combining oxygen with the reducing gas.
But what if you wanted to use atmospheric biosignatures, to find ETI instead of plain old dumb life?
So dumb
It has been suggested that we could look for signs of pollution in exoplanet atmospheres to guess at the presence of ETI. While high concentrations of molecules such as methane (CH4) and nitrous oxide (N2O) can be suggestive of polluting life, they can also be created by unintelligent sources. While finding weird amounts of CO2 can be explained away, looking at more exotic compounds (namely specific chlorofluorocarbons) can provide much stronger evidence that life exists. Not only are they only significantly produced by unnatural processes, but some of them have short lifetimes, which could constrain how recently the ETI was on that planet.
What is extra cool about these molecules is that in high concentrations (~10x what we have here on Earth), they should be detectable with ~1 day of JWST time (RIP early 2019 launch date) for a planet around a 6000K white dwarf.
If one wanted to be silly, they could suggest using these unnatural CFCs as a form of METI beacon to announce our polluting presence to the galactic club. Not that they’d want such a self-destructive member.
Only in truly engaging astrobiological, AI, transhumanist, global risk, and philosophical communities in fruitful interdisciplinary worldview can SETI truly achieve the respect and dignity that pioneers like Carl Sagan justifiably aspired to.
Amen! Preaching to the choir here. During my long experience with SETI (as of writing this, it has been almost eight whole weeks), I have slowly shifted my thoughts towards those beautifully reflected in this paper. Bradbury and co. point out that SETI used to be considered imaginative and maybe even daring, the field but has not continued to develop with the times. Many searches continue to be what the authors call “orthodox SETI” which is looking for signals at a particular frequency (usually radio), and this is what many think of when they think of SETI (aside from crackpots looking for little green men). The authors suggest expanding SETI to include artifact searches, or traces of a civilization that could remain past the civilizations lifetime. These searches also remove the assumption that the ET civilization is trying to contact us or otherwise alert us of their existence, an assumption that, while required to be able to search for beacons, might not be true.
This paper slightly amuses me in that it’s sort of a shaming of the field. The authors realized that the field had become stagnant, and this was apparently a good way to get it moving again? I’m not sure if this paper brought about any change, but as an idealist, I’d like to believe that it did. Since this paper, there seems to have been an emergence of artefact SETI (that the authors refer to as Dysonian SETI), but this might be a trend that I have only noticed through the diverse papers selected for this class. I will say that I have not noticed much on an increase in the interdisciplinary interactions of SETI, but I feel a lot of that is academics too embarrassed to join the field (or they think it BS). This is something that I really wish would change, as I’m sure many in the field wish also. Bringing SETI up-to-date with current technologies (oh, the irony), knowledge, and collaboration could really improve where the field is going, as well as improve its funding.
The theme between the Townes (1983) and Hippke & Forgan (2017) papers is that our SETI efforts should not be solely focused on searches in microwave and radio frequencies. These papers make the case that there are in fact equally viable if not superior alternatives to radio in both the infrared (IR) and X-ray portions of the electromagnetic spectrum, respectively. SETI experiments have been influenced by the precedent set by the earliest ideas in the field, which emphasized the radio search (and often near the 1.2-1.67GHz water hole). In fact, it was Cocconi and Morrison who gave us the idea that the most important factor when imagining interstellar communication systems is their efficiency in terms of photons per watt, which led them to pursue the radio search. However, with the development of new technologies and perspectives, it is clear that this narrow viewpoint misses out on a greater variety of possibilities.
These are examples of quality SETI papers because they attempt to expand our perspective and push boundaries. They remind us that we should be ever aware of falling into narrow-minded modes of thinking, and that when dealing with the perplexity of trying to predict the motivations and strategies of an ETI, we should stoically expect that we are wrong. They are also remarkable in their approach to the question. In the case of Townes, he thinks critically about the observational challenges of moving to the infrared and quantitatively compares the pros and cons of IR methods with those of microwave/radio. He is also cognizant of the fact that there are a lot of assumptions (which he makes explicit) made about the strategy of a transmitting ETI which we can only speculate about and limit the effectiveness of the IR search. On the other hand, Hippke & Forgan are motivated by the search of the global optimum for interstellar communication, which they decide ought to be in the X-ray near 1nm. In pursuit of this grail frequency, they examine a variety of astrophysical and observational difficulties which complicate communication, such as diffractive photon loss, interstellar extinction, and atmospheric transmission. In this way, both papers are firmly rooted in taking a classically quantitative and astronomical approach to SETI. This places these papers a tier higher than those which solely offer speculation on search strategies unsubstantiated by rigorous examinations of the merits of the alternative. Overall, the field benefits when scientists take SETI seriously and improve it by contributing to it with quality papers.
Wright views SETI as an interdisciplinary field, albeit one that is fragmented and mired by inconsistent jargon. In a recent paper presented at the SETI Institute Workshop, Wright attempts to organize the terminology and subfields of SETI into a unified framework. He explicitly states:
SETI [is] an interdisciplinary study that includes the humanities and social sciences, and a subfield of astrobiology that focuses on the detection of technosignatures (as opposed to biosignatures). Two major branches of SETI are communication SETI and artifact SETI (although the line between them is not always sharp), and others include METI and the search for “nature plus”.
Above is a comparison of “orthodox” SETI and “Dysonian” SETI. Wright argues that SETI as a whole is in between both of these extremes. The fact that each extreme focuses at difference frequencies and has different assumptions of advanced technological civilizations (ATC) suggests multi-discipline approach. The table is from Bradbury et. al. 2011.
Wright references the arguments brought by Robert Bradbury et. al. There are two primary extremes in SETI: (i) traditional SETI focusing on intentional messages primarily in the radio and (ii) Dysonian SETI focusing on artifacts and traces of advanced technological civilizations (see Table 1). Bradbury concluded that:
orthodox SETI is not only low probability in terms of success, it is also potentially risky, stunting and scientifically limiting […] We suggest that there is no real scientific reason for such situation. The regrettable condition of SETI is due to excessive conservativeness, inertia of thought, overawe of the “founding fathers,” or some combination of the three. Another, albeit extra-scientific, argument often put forward in informal situations is that the massive pseudoscientific fringe surrounding SETI (“flying saucers” enthusiasts, archaeo-astronauts, and the like) would feel encouraged by relaxing the conservative tenets of the orthodox SETI. […] The proposed and unconventional approach, with its emphasis on the search for the manifestations of ATCs would lose nothing of the advantages of conventional SETI before detection [63], but the gains could be enormous
For Bradbury, to focus on just radio SETI lacks scientific merit and appears to be done out of deference to the founders of SETI. Instead, both orthodox and Dysonian SETI should be viewed as one field requiring knowledge from various other subfields. Wright builds upon Bradbury’s conclusion by attempting to show that SETI is interdisciplinary. He notes that SETI can be performed at multiple wavelengths, such as the optical and near infrared. A lot of the examples provided; exoplanetary science, galactic and stellar astrophysics, time-domain astronomy, and multi-messenger astronomy easily make SETI part of physics and astrophysics. The case for interdisciplinarity becomes more concrete for the social sciences. Wright appears to argue for the need of xenology, using humanity as a logical stepping stone. This is a reasonable step and, while social sciences will inherently carry an anthropocentric view, it does allow for interesting dialogue with social scientists and practitioners of SETI.
Wright argues that for SETI to embrace multiple disciplines, it must standardize the jargon used by practitioners. While some of the terms he mentions are obscure (alien race), others such as “intelligence” and “beacon” have clear implications in what SETI is searching for and how to proceed. This blogger is largely in agreement with Wright. It makes no sense for SETI to be fragmented into many factions as they are all doing something to search for extraterrestrial life. Normalizing the language used is but one step. As mentioned by Bradbury, there still exists some stigma towards Dysonian SETI which hopefully disappears as more searches are performed.
In Wright (2018), the issue of SETI’s confusing taxonomy and several terms in SETI having multiple meanings is addressed.
SETI’s place in the scientific landscape is often confused. It is not clear to a majority of people where exactly SETI stands in relation to subjects like astronomy, biology, or their field of intersection, astrobiology. This paper seeks to place SETI (looking for evidence of technology) firmly in astrobiology as a separate, but equally valid approach for finding life (in comparison to looking for regular biosignatures).
Astrobiology taxonomy chart from the paper
In addition to clarifying where SETI lies as a subject, the paper focusses on asserting the importance of having an unambiguous set of definitions for commonly used jargon. As SETI is so interdisciplinary, terms are often hastily borrowed from other subjects and used in whatever sense may be useful to the current study, but this methodology is unnecessarily confusing for those who read multiple studies and are trying to understand the subject as a whole. Sample definitions for terms like beacon and ETI are defined while some terms are suggested to be avoided like colonization and civilization.
SETI’s highly interdisciplinary nature is emphasized in this paper by bolding every mention of a subject that isn’t SETI. While I think the method is heavy-handed, I don’t think that it is a wasted effort. It is cool to see just how many fields necessarily intertwine with SETI. Although, I would like to shame the editor for not ensuring a consistent usage of said bolding (the last paragraph on the left of page one: “the social sciences” versus the third to last paragraph on the right of page one: “the Earth sciences “). Shame.
In this post I shall discuss the white paper written by Jason Wright on the need for SETI to adopt standard terminology. The paper argues about the need for such an approach. In the era of advances in astrobiology, we need to find the right synergy between the two fields, and how SETI is rightfully a subset of astrobiology since it is also looking for signatures of life (biology) around celestial bodies.
The field of exoplanets has rapidly grown since the first discovery of an exoplanet around a star in 1995 [51 Pegasi b]. With advances in engineering and instrumentation we are slowly approaching the domain where we can detect the presence of an Earth like planet around a Sun like star in its habitable zone [Kasting 1991]. In tandem with this process of discovery, the characterization of exoplanetary atmosphere and climate has also progressed using spectroscopy techniques; attempts have been made to detect biosignatures in these spectra of exoplanets.
Closer home, we also have ‘potentially’ habitable objects, which could have harboured life in the past, or might have life in the present as well. Solar system bodies like Europa, Enceladus and Mars, are intriguing objects which might have the right conditions to sustain (or have sustained) life.
Astrobiology is generally touted to be limited to this search for biosignatures. However, as mentioned in the introduction, it must include not only biosignatures, but also technosignatures or signs of intelligent (advanced technologically) life.
A unified jargon is important in a diverse and interdisciplinary field like SETI which involves contributions and discourse from not only astronomers, but also engineers, anthropologists, linguists, and potentially cryptologists. The paper by cites the example of Artifact SETI, and how it should be an umbrella term for various kinds of searches.
An example of this that I have encountered (a situation nowhere as close to as significant as in SETI, however representative nonetheless), is when I tried to understand radio astronomer jargon in order to derive the relation between transmitter bandwidth and the sensitivity of a receiver. Being involved with optical and NIR astronomy, I am completely alien to radio astronomy. Despite both the fields being subsets of astronomy and governed by the same laws of Physics, there exist a large number of differences in how they measure and quantify similar parameters. It would have been very useful if they used the same terminology or in the least had some kind of a guide to bridge the two.
Now, if we take this situation and extrapolate it to collaborations between the sciences and humanities, this problem gets severely exacerbated. Hence, I think the framework adopted by this paper is necessary, and one that should be worked on as the field of SETI grows and involves collaborations from other fields and subjects.
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.
The primary conceit of the paper is that, as vegetation produces a reflective spectral “red edge”, artificial materials could produce similar reflective spectral signatures. These signatures, described in the paper as a distinctive change in reflectivity over a narrow bandwidth, could be detectable if they covered enough of an exoplanet’s surface.
A figure from the paper showing the vegetation red edge and the other edges from different artificial materials
The authors find that silicon produces one of these “artificial edges” in the ultraviolet. Even 10% coverage by silicon could be detectable in certain circumstances (tidally-locked planets around M-dwarfs) with next generation telescopes like WFIRST and JWST. Given an assumption about the composition and reflectivity of the material, you can easily get the coverage fraction. From that fraction, you can guess their power usage (this is assuming that the silicon signature is produced by large-scale photovoltaic arrays).
If you think this is a lot of solar panels, check out one of Lingam and Loeb’s planets
The element I most appreciated in this paper was the authors’ clear statement of assumptions and acknowledgements of alternatives and difficulties in their methods. They make it clear that their calculations are predicated on the idea that the civilization is getting their power supply from their host star, not from geothermal energy or nuclear fusion (which they state would cause other signatures, but they don’t try to predict them in this paper). They add caveats that would affect the signature’s detectability from Earth: hazy atmosphere on the planet, strong winds, and cloud cover. They give solid reasons for choosing silicon as the element to focus on in the paper, based on nucleosynthetic abundance, but also show some spectral signatures of other plausible bases for solar panels. Finally, they considered false positives that could also cause a similar signature, in particular a natural material called enstatite*, and ways to differentiate the two (eg. looking for energy redistribution on the surface of the planet from dayside to nightside).
All in all, I found this to be a very convincing and self-aware paper, and I’m very excited to see an artifact-search like this be conducted in the next decade or so!
* Some facts about enstatite (because part of me always wanted to be a geologist)! It’s a common mineral found in igneous and metamorphic rocks and is a 5-6 on the Mohs scale. It’s essential in some Earth mantle materials and is commonly found in asteroids. It has, in fact, been found in crystalline form in some planetary nebulae.
When enstatite is gem-quality, it’s apparently called “chrome-enstatite” and looks like this (thanks Wikipedia).
Settlement: “a process by which an intelligent species spreads to new areas”*
I have a pet peeve about concreteness. I have been to a few conferences now, and an overarching theme I’ve noticed is that someone will have a fascinating concept, but be kind of dodgy when asked about how to directly apply their concept to real methodology.
As an example, the idea of “ecoscenography” was proposed at an art + science + education conference I attended a few years back. The thesis is that theatrical performances can be extremely wasteful – sets are constructed, used once, and then discarded, and the entire process is disproportionately and unnecessarily harmful to the environment. I was involved in theatre for a long time, and was really interested, so I talked to the speaker about implementation (Reusing simple set elements by repainting? Using more recycled materials? A sharing program between schools for costumes/props/set pieces?), and they kept insisting that we should keep it broad, it’s more of a philosophy, and not define any specific techniques. Well, to be frank, that sounds like a great way for your idea never to be of any use to anyone.
A more “concrete” illustration of the power of ecoscenography
I bring this up because I wanted to clarify a point brought up in Taxonomy and Jargon in SETI as an Interdisciplinary Field of Study (the white paper that I presented at DAI 2018). Some of my peers, in telling them about my presentation, argued that one of the less useful-sounding and more pedantic arguments in that talk was the distinction between “colonization” and “settlement”. Here are three arguments I ran into:
We shouldn’t worry about offending / being politically correct to a species we haven’t met yet, that we may never discover the existence of!
Putting a nice skin on the idea of “colonization” by calling it “settlement” is a little bit offensive in a way – it delegitimizes and hides the ugly parts of the analogous historical situations
It doesn’t matter at all to the actual science of SETI and seems like a quibble over synonyms
Here’s my response to those arguments, after a few weeks of on and off pondering. This is not a paper about political correctness, either in its favour or against it. This is a paper that argues that the lack of precise and accurate terminology hinders the logistical workings of and the intellectual vibrancy/creativity of SETI more than in other fields, and we should recognize and take steps to fix that.
If I were as general as the talks that I berated for lack of concreteness in the earlier part of this post, I would leave it at that. But because I’m not, I want to take on this particular example.
“a process by which a central system of power dominates the surrounding land and its components”
Comes from the Latin colere meaning “to inhabit”
Britain would consider new land as terra nullius (empty land) due to the absence of European farming techniques (regardless of the presence of other populations)
conflict between colonizers and local/native peoples
motivations being trade or “shorter-term exploitation of economic opportunities”
“absorbing and assimilating foreign people into the culture of the imperial country”
In science fiction, “sometimes more benign” – word is used very often
Here are some questions that this article brings up, for me (and, in parentheses, some search implications of each broken assumption):
Habitable worlds ripe for the picking… or not?
Why should we assume that an alien race would want to colonize in the first place? (searching for clusters of systems that have similar signatures becomes a poor search strategy)
What if ETI is NOT spreading for the purpose of resource acquisition and energy demand? (maybe black hole energy-farming is a bad thing to look for, shouldn’t look in places that humans would think are valuable (ex. asteroid belts), could be some underlying pattern in the spread based on religious/cultural/societal reasons behind it))
What if the ETI is conscious of their environment and co-exists with the surrounding land? (no technosignatures would appear during the spread)
What if the ETI is peaceful and co-exists with the inhabitants? (multiple different kinds of biosignatures or technosignatures could co-exist in a single area / N could be higher than one would calculate assuming “domination”)
What if the ETI puts von Neumann probes in systems for scientific or other purposes, but does not actually biologically inhabit it? (we shouldn’t just look at biologically-friendly environments like FGK stars)
What if a certain ETI has a very different idea of terra nullius? What if the presence of microbial life will limit the spread of an ETI because, to them, those environments are “already taken”? (we should look for technosignatures where there are no simple biosignatures already)
What if an ETI is a perfect, Sagan-esque archetype and lifts lesser species out of poverty/technological-infancy instead of causing conflict? (look for geographically-grouped, expanding technosignatures, rates of technological development become geographically dependent)
Is our acceptance of the more general, less problematic interpretation of “colonization” in SETI derived from our science fiction instead of our science? (we stick to a term that doesn’t make lexical sense based on stubbornness and end up making some of the other assumptions in this list)
The point of these questions isn’t that any particular suggestion I made is a good idea. A lot of them are not, or violate other fallacies (like the monocultural fallacy, for example). But it’s obvious that if we look closely at the relatively straightforward logical steps that follow from the dictionary definition of “colonization”, all sorts of SETI search strategies end up being implicitly excluded or assumed. Are we self-aware enough to say “well, I know what the word implies, but I wouldn’t let that affect my science in such obvious, drastic ways” and succeed in that quest? I don’t know about anyone else, but I don’t think I’m self-aware enough for that. I’m sure there are some assumptions hidden in here that I’ve missed. I am, after all, only human!
So in your next publication, dear reader, please use the word “settlement” instead of “colonization”. Your science will thank you.
To add an additional complication at the end of this blog post: I discovered that in biology, colonisation or colonization means “a process by which a species spreads to new areas”. This definition has the perfect lack of connotations that we’re looking for in SETI, and would be a strong argument to continue using the word. My response: SETI is a subset of astrobiology, so we will be interacting with people who DO use this definition. Most practitioners, however, will still have the historical connotations in their head (because that’s what we’ve been exposed to, socially, and humans aren’t very good at putting that sort of conditioning out of our heads). To get around this confusion, in SETI, we should take “settlement” to have the definition I posit at the top of the page.
My opinion of this paper is completely biased by the fact that I’ve actually met David Kipping and that I read this paper back when it first went on the arxiv. This was my first exposure to SETI (beyond science fiction, if that counts) and I think it went well!
Kipping and Teachey postulate that a civilization (even the Earth) could use lasers in some interesting ways. They first suggest that a planet’s transit could be clocked, monochromatically, against a Kepler-like survey, without the need for much power (~30MW). Due to the Earth’s rotation, this would require multiple laser stations, but in the end, it would be doable. They then continue on to talk about clocking the signal at all wavelengths. This would be a bit more challenging, since many lasers at many different lasers would be required, and again these lasers would need to be placed around the planet, and the power requirement would increase by an order of magnitude, but a committed civilization could manage it. Both of these cloaking processes can be argued against since the planet would still be detectable via other detection methods (namely RV).
The last bit of cloaking they suggest involves the cloaking of biosignatures. A disequilibrium in an atmosphere (normally of oxygen) is a decent indication of life on a planet. These and other related absorption features are referred to as biosignatures. If lasers were emitted at these absorption features, then the planet would still be detected and noticed, but it would just not be studied much since it would be presumed uninhabitable. This is all, of course, under the assumption that other life out there is Earth-like, and that this Earth-like life would be looking for signatures similar to their life (Earth-like). Because of this Earth-like assumption, it is possibly that another civilization is already doing this for *their* biosignatures, we just don’t notice it though because we are looking for our biosignatures (also clouds are apparently all that we can see right now).
Lastly, the authors bring up the point that this laser method can be used not just to cloak, but also to signal existence. They briefly mention that the easiest way to get someone’s attention with this would be to cloak the transit’s ingress and egress, making the transit appear boxy and all around wrong.
Although this is a neat idea, it seems a little far fetched and specific to me. Sure, we have tons of data, so someone might as well look through for boxy transits (I think someone has already done this with Kepler data), but this seems so absurdly unlikely to happen. However, my thoughts on the likelihood of this completely come from the way I view humanity and our goals and motivations, so it’s just as possible that my thoughts of this being a waste are a minority in the galaxy.
