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A Path Forward for Technosignature Searches

Héctor Socas-Navarro (Instituto de Astrofísica de Canarias) is lead author of a paper on technosignatures that commands attention. Drawing on work presented at the TechnoClimes 2020 virtual meeting, under the auspices of NASA at the Blue Marble Space Institute of Science in Seattle, the paper pulls together a number of concepts for technosignature detection. Blue Marble’s Jacob Haqq-Misra is a co-author, as is James Benford (Microwave Sciences), Jason Wright (Pennsylvania State) and Ravi Kopparapu (NASA GSFC), all major figures in the field, but the paper also draws on the collected thinking of the TechnoClimes workshop participants.

We’ve already looked at a number of technosignature possibilities in these pages, so let me look for commonalities as we begin, beyond simply listing possibilities, to point toward a research agenda, something that NASA clearly had in mind for the TechnoClimes meeting. The first thing to say is that technosignature work is nicely embedded within more traditional areas of astronomy, sharing a commensal space with observations being acquired for other reasons. Thus the search through archival data will always be a path for potential discovery.

The Socas-Navarro paper, however, homes in on new projects and mission concepts that could themselves provide useful data for other areas of astronomy and astrophysics. A broad question is what kind of civilization we would be likely to detect if technosignature research succeeds. Only technologies much superior to our own could be detected with our current tools. Recent work on a statistical evaluation of the lifespan of technological civilizations points to the same conclusion: First detection would almost certainly be of a high-order technology. Would it also be a signature of a civilization that still exists? As we’ll see in the next post, there are reasons for thinking this will not be the case.

Image: Artistic recreation of a hypothetical exoplanet with artificial lights on the night side. Credit: Rafael Luis Méndez Peña/Sciworthy.com.

This is a useful paper for those looking for an overview of the technosignature space, and it also points to the viability of new searches on older datasets as well as data we can expect from already scheduled missions and new instrumentation on the ground. Thus exoplanet observations offer obvious opportunities for detecting unusual phenomena as a byproduct of their work. The workshop suggested taking advantage of this fact by modeling, with technosignatures in mind, for complex light curve analysis, photometric and spectroscopic searches for night-time illumination, and developing new algorithms for analyzing optimal communications pathways between exoplanets in a given volume of interstellar space:

A region of space with the right distribution of suitable worlds to become a communication hub may be a promising place to search. TS [technosignatures] might be more abundant there, just like Earth TS are more abundant wherever there is a high density of human population, which in turn tends to clutter in the form [of] network structures.

Other methods piggyback on existing exoplanet campaigns. Observing planetary atmospheres, for instance, is useful because it ties in to existing biosignature detection efforts. Future projects on missions observing in the mid-infrared like the Large Ultraviolet Optical Infrared Surveyor (LUVOIR) could explore this space. See Technosignatures: Looking to Planetary Atmospheres, for example, for Ravi Kopparapu’s work on nitrogen dioxide (NO2) as an industrial byproduct, a kind of search we have only begun to explore. Back to the paper:

A nice advantage of this method of detecting atmospheric technosignatures is that the same instruments and telescopes can be used to characterize atmospheres of exoplanets. Our view of habitability and technosignatures is based on our own Earth’s evolutionary history. There are innumerable examples in the history of science where new phenomena were discovered serendipitously. By having a dedicated mission to look for atmospheric technosignatures that also covers exoplanet science, we can increase our chances of detecting extraterrestrial technology on an unexpected exoplanet, or may discover a spectral signature that we usually do not associate with technology. The only way to know is to search.

Where else might we push with new observational and mission concepts? A 3-meter space telescope performing an all-sky survey with high point source sensitivity in the infrared could provide benefits to astrophysics as well as being sensitive to Dyson spheres at great distances. The paper argues for a dedicated effort to develop fast infrared detectors capable of nanosecond timing to enable a space mission searching the entire infrared sky. Such detectors would be sensitive to transients like pulsars and fast radio bursts as well as broadband pulses.

The paper also makes the case for a radio observatory on the far side of the Moon. Here we are all but completely free from contamination from radio interference by our own species, although even now the matter is complicated by satellites like China’s Queqiao, which has been at the Earth-Moon L2 Lagrange point for almost three years. Issues of radio protection of the far side will grow in importance as we try to protect this resource, where Earth radio waves are attenuated by 10 orders of magnitude or more. Again, we are dealing with a future facility that would also be of inestimable value for conventional astronomy and lunar exploration.

Close encounters with other stars (which occur as another star penetrates the Sun’s Oort Cloud every 105 years or so) highlight the possibility that extraterrestrial civilizations, having noted biosignatures from Earth, could have placed probes in our system. Few searches for such artifacts have been conducted, but as Jim Benford has discussed in these pages (see Looking for Lurkers: A New Way to do SETI) a host of objects could be easily examined for artifacts. Few have been studied in depth, but Benford has made the case that both the surface of the Moon and the Earth Trojans can now be studied at an unprecedented level of detail.

We already have monthly mapping of the Moon at high resolution via the Lunar Reconnaissance Orbiter (LRO) with a resolution of 100m/pixel (LRO can also work at a higher resolution mode of 0.5m/pixel, but this mode has not been widely used). Future exploration might include an orbiter working in ultra high-resolution at the ∼10cm per pixel level. The workshop also discussed high-resolution mapping of Mars and, perhaps, Mercury and larger asteroids coupled with machine learning techniques identifying anomalies.

Not surprisingly, given the high visibility (in public interest) of objects like ‘Oumuamua or 2I/Borisov, a ready to launch intercept mission also comes into consideration here to plan for the study of future interstellar arrivals. Other possibilities for pushing the technosignature envelope include an asteroid polarimetry mission studying either main belt asteroids or the Jupiter Trojans, gathering information that would be useful for our understanding of small objects with a potential for impact on the Earth. The Jupiter mission could probe for natural and possible artificial objects that might have wound up being ensnared over time in Jupiter’s gravitational well. The asteroid mission would produce a statistical description of small objects in solar orbit. The paper describes it this way:

A telescope similar to Kepler would be sensitive to objects of 10 m up to a distance of 0.02 AU (assuming a high albedo of 0.8) or 0.01 AU for typical asteroid albedos. Extrapolating the current knowledge of asteroid size distribution, there should be some 250,000 asteroids of 10 m in the radius of 0.02 AU accessible to such [a] telescope in the asteroid belt. The mission could be designed with an elliptical orbit having the perihelion near the Earth’s orbit and the aphelion in the asteroid belt. Under these conditions it would regularly dive into a different region of the belt, probing a different space in every orbit.

Such are some of the ways we can extend the search for technosignatures while supporting existing astronomical and astrophysical work. The paper goes into new ground in introducing a framework for future work for the different types of technosignatures, defining what it calls the ‘ichnoscale’ and analyzing it in relation to the number of targets and the persistence of a possible signal. The ichnoscale parameter is “the relative size scale of a given TS [technosignaure] in units of the same TS produced by current Earth technology.“

We’re only beginning to map out a path forward for technosignature investigation, but the authors believe that given advances in exoplanet research, astrobiology and astrophysics, we are at the right place to inject new energy into the attempt. Thus what the community is trying to do is to learn the best avenues for proceeding while developing a framework to advance the effort by quantifying targets and potential signals. Along the way, we may well discover new astrophysical phenomena as a byproduct.

I’m particularly interested in the thorny question of how long technological civilizations can be expected to live, and am looking into a new paper from Amedeo Balbi and Milan Ćirković on the matter. I’ll be exploring some thoughts from this paper in the next entry.

The paper for today is Hector Socas-Navarro et al, “Concepts for future missions to search for technosignatures,” Acta Astronautica Volume 182 (May 2021), pp. 446-453 (abstract / preprint).


Comments on this entry are closed.

  • Alex Tolley March 15, 2021, 13:19

    An argument has been made by some that scientists are too conservative in their thinking about ETIs, especially concerning premature claims of existence. This paper at least puts forward a rational strategy to search for ETI using a range of possible technosignatures (TS).

    However, I am now going to suggest that this search is far too conservative in its thinking about ETI, anchored in our species’ actions in the early 21st century while also suggesting that any TS is likely to be from a far more advanced civilization.

    An example. Currently, terrestrial cities are brightly lit as we have cheap energy and increasingly efficient lighting devices. At night, some Asian cities look positively dazzling to the eye compared to some European cities. This seems to be reflected in our Scifi movies since BladeRunner. However, humanity is starting to realize the damage light pollution is causing to our ecosystems, and there is an [small] effort to find ways to reduce that pollution and restore nighttime darkness. Will humans take this more seriously with future cities becoming much darker on the surface, with illumination kept inside structures, thus reducing the bright city light TS that is one target of the paper? IOW, while today satellite detection of night illumination is indicative of local GDP, with famously dark N. Korea almost a calibration marker, might a future Earth record higher GDP with lower exposed illumination? I would also note that a machine civilization needs no artificial illumination at all. Today, some automated factories are dark. Even mobile robots may use different senses for detecting and understanding their local environment, eliminating light pollution. [I see satnav navigation and self-driving transport resulting in a removal of visual navigation and driving signs, as well as making unsightly roadside billboards uneconomic].

    There must be a large number of current human TSs (e.g. CFCs, particulates, NOx, CH4, CO) in the atmosphere that will be absent with newer technologies for energy, transport, and food production. Centralized energy production may become diminished as distributed energy generation becomes economically viable. ICE-powered transport may disappear as we decarbonize our economy. Even conservative agricultural practices may give way to more controlled enclosed crop production, increasing productivity while restoring the once displaced ecosystems.

    Less than 2 centuries ago, the Victorian era saw smokestacks as a sign of progress and prosperity. The “Satanic Mills” of Northern England were a reality. Today the mills have disappeared and we no longer equate incomplete coal combustion as a metric of progress.

    So I would implore such conferences to include science fiction writers to imagine scenarios of our, and very alien, advanced civilizations to think about what might be more probable TSs of these civilizations and to think outside the box of our currently somewhat blinkered, anthropocentric thinking.

    [I think it was Dr. David Brin who proposed a website/FB group with the concept that there may well have been a sci-fi story that captured so-called new ideas. Perhaps what we need is a database of such ideas mined from the trove of a century of sci-fi stories that can be interrogated by the hive for TS ideas, however outré they may be.]

  • Geoffrey Hillend March 15, 2021, 15:44

    If all civilizations become technological and eventually build warp drives, then not a single one of them has died. They don’t die baring extinction events like gamma rays bursts from Wolf-Rayet stars, magnetars etc.

    • DCM March 16, 2021, 4:03


  • Ashley Baldwin March 15, 2021, 17:14

    I have to admit to being a big fan of the Clarke Exobelt concept . Unlike many technosignatures ( I’m looking at you CFCs) it has a lifetime in the 100000 year plus range ( for eta Earths around sunlike stars – longer for extended geosynchronous zones of larger terrestrial planets ). Nothing on an astrophysical scale for sure, but long in relation to an advanced civilisation’s duration. Detectable by contemporary or near contemporary transit photometry technology ( PLATO ?) too. To a distance of a kilo parsec too according to this article.

  • Wojciech J March 16, 2021, 7:22

    Two quick thoughts on the subject:
    “Only technologies much superior to our own could be detected with our current tools.”
    While correct, there is a certain caveat to this, only technologies that are near our imagined abilities will be identified as such. It has been argued before that truly advanced technology might be identified as indistinguishable from nature. A curious galaxy formation, or code embedded into laws of physics would be too much for us to accept as work of intelligence.

    “A region of space with the right distribution of suitable worlds to become a communication hub may be a promising place to search”

    I always wondered if systems such as Xi Scorpii would be a prime real estate for settlement and interstellar civilizations, having possibly rich planetary systems surrounding relatively habitable stars in easily reachable range of communication and travel with each other.


    • Alex Tolley March 16, 2021, 12:00

      While correct, there is a certain caveat to this, only technologies that are near our imagined abilities will be identified as such. It has been argued before that truly advanced technology might be identified as indistinguishable from nature. A curious galaxy formation, or code embedded into laws of physics would be too much for us to accept as work of intelligence.

      Or, a high density of planets stably orbiting in the HZ.
      Or, a planet not in the HZ, but having a clear biosignature.

      Having just reread Hoyle’s “Fifth Planet” (stimulated by a recent prior post), the crews land on what looks like a natural world, albeit where the only life appears to be grass. In fact, the aliens are extremely advanced and only anomalies and an accidentally exposed technology indicate their presence. [Sadly, none of the crew even question the strangeness of such a uniform global ecosystem, even though it cries out to any biologist, “this cannot be real”, and would invite at least some examination of the grass, taking soil and water samples, and looking at them under the microscope back at the ships. Lem’s “Solaris” seems far more real, with active science being done even as the few remaining science crew are plagued with manifestations.

  • Hamilton1 March 16, 2021, 7:47

    “The only way to know is to search”

    Once again we see the professionals placing limits on alien capabilities. For all we know, the technosignature might be brighter than any natural object in the sky – no need to search. At the risk of repeating myself, Columbus did not require the natives to construct a harbour.

  • Robin Datta March 16, 2021, 18:53

    While it may well be that we will more easily detect advanced civilizations, one of the references in comments to the preceding post noted that we might not detect FTL travel through our solar system; and one of the commenters above rightly reminded us that a sufficiently advanced civilization’s footprints may be indistinguishable from natural processes. The disruptions of matter and energy could be so slight as to be undetectable or overlooked. Or they may preferentially manipulate space and time instead of matter and energy to meett their ends.

    One factor in a civilization’s longevity could be the duration of its species. The changing environment associated with civilizational change can select through genetic drift, mutation and gene flow for faster changes in the genome with speciation. Even geographic variants that have emerged in Homo sapiens in its brief tenure on this planet are a source of contention.

    While some species such as the horseshoe crab have persisted with little or no change for a few hundred million years, most vertebrate species survive for a few million years before going extinct or transforming into other species. Three million years ago there were almost a dozen species of humanoids, of which we are the “last man standing”. We should not expect our species to survive untransformed into Deep Time.

    But what derives from biology on this planet may not necessarily be a yardstick applicable elsewhere.

  • Dmitry Novoseltsev March 17, 2021, 0:55

    https://i4is.org/wp-content/uploads/2019/11/Principium27-print-1911280846-comp.pdf, p. 3
    https://i4is.org/wp-content/uploads/2020/05/Principium29-print-2005271554opt.pdf, p.15
    Now my company D-Start is conducting experiments on ground tests of the current model of the engine. The preparation of the bench equipment is being completed.
    I hope to get the first real spectra that can be accepted as samples of technomarkers by the fall of 2021.

  • Michael Fidler March 31, 2021, 6:47

    China is planning HABITATS (HABItable Terrestrial planetary ATmospheric Surveyor) space telescope to search for earth-like exoplanets. With a giant 4-meter lens, it will be deployed at Sun-Earth L2 where Chang’e-5’s orbitor is currently flying.

    “we proposed the ambitious HABITATS (HABItable Terrestrial planetary ATmospheric Surveyor), a space telescope project dedicated to studying the atmosphere of exoplanets. It will stand on the shoulders of predecessors of the sky survey, obtain a large amount of information through spectral observations, improve human understanding of the nature of planets, explore the nature of super-earths and terrestrial planets in the habitable zone, search for possible signals of life, and open human research on planets , A new chapter in understanding the universe.
    The planned neighbourhood will be a lightweight space telescope with a caliber greater than 4 meters, serving in the Sun-Earth L2 orbit 1.5 million kilometers away. The L2 orbit can provide excellent dynamic stability and thermal environment stability, as well as the ability to continuously observe a single star for a long time. Tianlin will adopt a single-mirror off-axis three-mirror system. The plan includes four major astronomy systems, including a high-stability pointing imaging sensor, a high-contrast coronagraph, a high-resolution spectrometer in the ultraviolet to optical band, and a low-resolution spectrometer in the near-infrared band. equipment. It is planned to apply a simple and mature optical system, and the movable parts will be reduced as much as possible during the design, thereby greatly reducing the risk of this project and increasing the design operating life. At the same time, such a stable system will have very high stability and accuracy, making it possible to observe planetary systems in a habitable zone like the Sun-Earth, which is difficult for general large-scale space telescopes including JWST.”


    This is a single large off axis main mirror, could the design be similar to the PROJECT BLUE space telescope plans only much larger? https://arxiv.org/abs/1510.02489.