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arxiv: 2605.21093 · v1 · pith:UNNMQIN6new · submitted 2026-05-20 · 🌌 astro-ph.EP · astro-ph.IM· astro-ph.SR

The Search for Technosignatures: a Review of Possibilities

Cl\'ement Vidal , Benji L. Fields , Damian R. Sowinski , Mark Elowitz , Stuart Bartlett , Richard J. Terrile , Alex Ellery , Daliah Bibas
show 13 more authors
Armando M. Mastrogiovanni Niklas D\"obler Manika Singla Julia DeMarines Theresa Fisher Yuri Uno Jake D. Turner Evan L. Sneed Advait Huggahalli Megan Grace Li Zhuofu (Chester) Li Macy Huston Ramiro Saide
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Pith reviewed 2026-05-21 01:57 UTC · model grok-4.3

classification 🌌 astro-ph.EP astro-ph.IMastro-ph.SR
keywords technosignaturessearch for extraterrestrial intelligenceKardashev scalebiosignaturesexoplanetsinterstellar communicationanomaly detection
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The pith

Technosignatures can be organized by spatial scales from Earth to galactic levels to guide systematic searches.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This review compiles the range of technosignatures proposed across the scientific literature and structures them according to increasing distance and size, beginning with Earth-based examples and extending outward through solar system locations, exoplanets, stars, and interstellar and galactic phenomena. It incorporates established frameworks like the Kardashev and Barrow scales to classify energy and information processing activities while also addressing detection methods, synergies with biosignature searches, and strategies for prioritizing observations. A reader would care because this scale-based catalog turns scattered ideas into a practical map that can inform where and how to look for evidence of extraterrestrial technology with current and future instruments.

Core claim

The paper reviews proposed technosignatures by organizing them according to spatial scales, beginning with Earth and progressing through Earth's orbit, the solar system including the Moon and Lagrange points, the asteroid belt, interstellar objects, the outer solar system, the Kuiper belt, the solar gravitational lens, and the Oort cloud. It then applies the Kardashev and Barrow scales before examining exoplanetary signatures at surface, atmospheric, and orbital levels, followed by stellar modifications and pollution, compact object signatures, interstellar communication across multiple search dimensions, interstellar travel signatures, and finally galactic, extragalactic, and universal ones

What carries the argument

Scale-based organization of technosignatures, from local planetary to galactic levels, incorporating the Kardashev scale for energy use and the Barrow scale for information processing to structure the search space.

If this is right

  • Searches can start with accessible local scales such as Earth orbit or the asteroid belt before moving to more distant targets.
  • Multimodal observations can combine technosignature and biosignature indicators at overlapping scales like planetary atmospheres.
  • Detection instruments can be matched to specific scales, for example focusing on orbital artifacts or stellar pollution signatures.
  • Prioritization of search efforts can use the scale map to identify gaps in coverage from current telescopes.
  • Anomaly detection algorithms can be tuned to flag unusual signals at each scale level.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Adopting this scale organization could encourage new proposals for signatures at intermediate locations such as the solar gravitational lens region.
  • The framework might connect to broader anomaly detection work in astronomy by providing categories for classifying unexpected observations.
  • Future data releases from wide-field surveys could be cross-checked against the scale categories to test how much of the search space has been examined.

Load-bearing premise

The collected literature accurately captures the main ideas in the field and that grouping them by spatial scale creates a useful framework for planning searches without requiring new observational proof.

What would settle it

A concrete technosignature proposal that cannot be placed at any reviewed scale, or a set of targeted searches using this scale organization that consistently misses candidates later found by unorganized methods.

Figures

Figures reproduced from arXiv: 2605.21093 by Advait Huggahalli, Alex Ellery, Armando M. Mastrogiovanni, Benji L. Fields, Cl\'ement Vidal, Daliah Bibas, Damian R. Sowinski, Evan L. Sneed, Jake D. Turner, Julia DeMarines, Macy Huston, Manika Singla, Mark Elowitz, Megan Grace Li, Niklas D\"obler, Ramiro Saide, Richard J. Terrile, Stuart Bartlett, Theresa Fisher, Yuri Uno, Zhuofu (Chester) Li.

Figure 1
Figure 1. Figure 1: The Drake equation addresses the many factors used to estimate the number of civilizations producing technosignatures in our galaxy at any given time. could be much more dynamic and complicated than we imagine while guided by the Drake equation only. We do not aim at a critical and detailed evaluation of each technosignature that we review: even the different authors of the present paper would certainly di… view at source ↗
Figure 3
Figure 3. Figure 3: The UAP Taboo: vicious circles prevent serious studies of UAPs. History repeated itself half a century later as UFO was changed to “Unidentified Aerial Phenomena” (UAP) in Project Condign, led by the UK Ministry of Defence (Defense-Intelligence-Agency 2000). The “A” of “Aerial” also shifted to “Anomalous”, for example by the “All-Domain Anomaly Resolution Office” (AARO 2024) and therefore encompassing a gr… view at source ↗
Figure 4
Figure 4. Figure 4: Decision tree illustrating the possible categorizations for UAPs. About 90-95% of cases end up being explained, but about 5-10% remain unexplained, and will likely eventually be explained in the future (see [PITH_FULL_IMAGE:figures/full_fig_p009_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Nine simultaneously occurring transients on April 12th 1950, from Villarroel et al. (2021): 10 x 10 arcmin field shown in POSS-1 and POSS-2 red bands. In the POSS-1 image we see a number of objects that cannot be subsequently found, marked with green circles. Purple circles are artifacts during the scanning process. About 9 objects are present in the POSS-I E image (left) from the 12th of April, but not in… view at source ↗
Figure 6
Figure 6. Figure 6: Left: An LRO/LROC image showing the Apollo 12 descent module and astronaut tracks located at selenographic coordinates 3.0128 S, 336.57810 E. Two extravehicular (EVA) activities were performed on the lunar surface totaling 7.75 hours, resulting in the collection of 35.34 kg of lunar samples. Right: An LROC image showing the Apollo 17 landing site. The sub-meter resolution image clearly shows the descent mo… view at source ↗
Figure 7
Figure 7. Figure 7: LRO LROC-NAC frame M118769870LC of the unusual structures located on the floor of the lunar farside crater Paracelsus C. The image shows complex geometrical structures and three-dimensional relief as evident by the cast shadows. At a spatial resolution of 0.5 meters, details as small as 1 meters can be seen, assuming that two pixels are required to resolve features in the image. The inset shows an enlargem… view at source ↗
Figure 8
Figure 8. Figure 8: The five Lagrange points of the Earth-Moon system in the co-rotating reference frame. Gravitational potential contours (logarithmic scaling) are superimposed on the gravitational field lines (streamlines). The first three Lagrange points occupy saddle points (blue dots) of the potential, while L4 and L5 local maxima (red points). Counterintuitively, these are dynamically stable when Coriolis forces are tak… view at source ↗
Figure 9
Figure 9. Figure 9: The Solar Gravitational Lens (SGL) is a region where gravitational and neutrino radiation starts to focus (respectively at 22.45 AUs and 29.6 AUs) while the focus of electromagnetic (EM) rays starts from 547 AUs. Human or ETI observational or transmitting probes placed at these regions would benefit orders of magnitude of gains. Figure adapted from (Maccone 2009, page xxxi). and Wright (2021) suggested tha… view at source ↗
Figure 10
Figure 10. Figure 10: Total human energy use through time on the Kardashev scale. Depending on the definition of energy usage we have a lower-bound (black line) and an upper bound which adds the agricultural burning of biomass (green dot-dashed line). Slight variations from the literature on the definition of K result in indices ranging from 0.55 to 0.76, classifying modern human civilization between a Type-0 and Type-I [PITH… view at source ↗
Figure 11
Figure 11. Figure 11: The Barrow scale highlights the ability to manipulate and control from our own scale (1m) to the minimal length-scale (10−35 m) . Humanity has created many tools at our own human scale down to the nanotechnological realm (green), but has almost no mastery below (red). Barrow (1998) gave examples of types: Type I-minus: The ability to manipulate objects on a human scale, such as building structures and min… view at source ↗
Figure 12
Figure 12. Figure 12: Spectra of four types of artificial lights. LED (blue spectrum) is clearly distinguished from the other three types of light sources. The incandescent (olive/green spectrum) has no emission lines, in contrast to the sodium and fluorescent light sources, which display a variety of unique emission lines. Future large-aperture space telescopes equipped with visible/near-IR spectrometers could detect (and pot… view at source ↗
Figure 14
Figure 14. Figure 14: (Top) A simulated transit depth spectrum showing SF6 and NF3 in the atmosphere of terrestrial exoplanets of different atmospheric compositions orbiting an M Dwarf star. The concentrations of SF6 and NF3 are at 1 ppm. (Bottom) Absorption cross sections for various atmospheric molecules, including the industrial produced SF6 and NF3. It is noted that concentrations of 1 ppm for both SF6 and NF3 are orders o… view at source ↗
Figure 15
Figure 15. Figure 15: Kepler observations of Boyajian’s star (KIC 8462852) dips. Dip numbers (in blue) correspond to 4 of the 10 discrete dips analyzed in (Boyajian et al. 2016). a civilization could wirelessly beam the immense energy collected by the swarm to power habitats, colonies, and projects throughout their star system. The construction of the swarm would require a highly advanced interstellar mining and manufacturing … view at source ↗
Figure 16
Figure 16. Figure 16: The left panel displays a simulated transit light curve and a scaled visual inset of a natural, Earth-like exoplanet passing in front of a sun-like star, causing a brief dip in brightness. In contrast, the right panel illustrates a highly complex light curve produced by an artificial Dyson swarm as its various panels orbit and cross the star’s disk. Comparing these two scenarios highlights how the intrica… view at source ↗
Figure 17
Figure 17. Figure 17: A blue band light curve for V816 Centauri (Przybylski’s star), adapted from (Kurtz and Wegner 1979). Wikimedia CC BY-SA 4.0. level nuclear fission waste products would remain in the photosphere of a star, and would be detectable in its stellar spectrum. A candidate is Przybylski’s (1961) star (see [PITH_FULL_IMAGE:figures/full_fig_p029_17.png] view at source ↗
Figure 18
Figure 18. Figure 18: Schematic diagram of a general communication system after Shannon (1948). from satisfying curiosity or collaboration, then the Nash equilibrium implies that it is advantageous to immediately attack any source of a detected signal while remaining silent. This gloomy conclusion is also known as the “Dark Forest” (Yu 2015) after the famous science fiction novel by Liu (Liu 2015). Another fundamental issue is… view at source ↗
Figure 19
Figure 19. Figure 19: Strategies to look for signals. Two dimensions are represented here: archival vs. real-time in the x-axis, and targeted vs. wide-field in the y-axis. has the advantage of being fast, and does not require infrastructure related to storage. The disadvantage is that only the kinds of technosignatures that are considered worthwhile at a certain time are examined, and it is impossible to go back to deleted dat… view at source ↗
Figure 20
Figure 20. Figure 20: A schematic illustration of a X-ray Free Electron Laser (XFEL). An electron gun fires a beam of electrons that are directed through an undulator after being accelerated through a particle accelerator. The beam of electrons then passes through an undulator, which is a periodic arrangement of magnets whose function is to produce the highly coherent X-ray pulses/beam. Diagram courtesy of Wikipedia, based on … view at source ↗
Figure 21
Figure 21. Figure 21: Moore’s law in spectral channels, from (Tarter et al. 2009). Frequency Comb”. He also emphasized that there are still inevitable anthropocentric choices when making such suggestions. Kardashev (1979) did also consider cosmological parameters, namely the range of maximum intensity of the cosmic microwave background. Astronomical Schelling points Astronomical phenomena can also provide natural timing and fr… view at source ↗
Figure 22
Figure 22. Figure 22: From communication intents to communication solutions, and their associated technosignature search strategies [PITH_FULL_IMAGE:figures/full_fig_p048_22.png] view at source ↗
Figure 23
Figure 23. Figure 23: ). As Heller (2017) noted, reaching 0.1c would not happen before 150 years from now, assuming this exponential growth continues unabated. In that sense, the project might have been a few centuries ahead of its time! [PITH_FULL_IMAGE:figures/full_fig_p051_23.png] view at source ↗
Figure 24
Figure 24. Figure 24: This simulation models the unique gravitational wave ”fingerprint” produced by a massive alien spacecraft decelerating toward our solar system. The resulting signal features a distinct, ripple-like waveform that represents changing deceleration over time, mapped by its pitch (frequency) and strength (strain). Ultimately, this unusual structure could allow scientists to easily distinguish an artificial, ma… view at source ↗
Figure 25
Figure 25. Figure 25: Illustration of a gravitational machine (Dyson 1963) for accelerating spacecraft using binary star orbital energy. Diagram based on Mallove and Matloff (1989, p. 141). 7.7. Newtonian gravitation for propulsion A universal strategy to gain energy and momentum is to harness gravitational energy by doing gravity assists. In this line of thinking, Dyson (1963) proposed the concept of a gravitational machine w… view at source ↗
Figure 26
Figure 26. Figure 26: The York-time representation of an Alcubierre spacetime bubble, showing a localized region of warped space with contracted space ahead and expanded space behind. Another hypothetical challenge with warp drives is that particles with an initial positive velocity in the spacetime bubble’s path are swept up and accelerated. During the collapse of the bubble, these particles produce a concentrated beam of ext… view at source ↗
Figure 27
Figure 27. Figure 27: An embedding diagram of the t = 0, θ = π/2 spatial slice of the Ellis wormhole. Ellis wormhole (ℓ ∼ 10−35m) requires a Gigajoule of negative energy. Morris–Thorne Solution —Morris and Thorne popularized the idea of traversable wormholes with this example (Morris et al. 1988). Their metric represents a static, spherically symmetric wormhole: ds2 = −e 2Φ(r) c 2 dt2 + dr2 1 − b(r)/r + r 2 dΩ 2 (8) Φ(r) is th… view at source ↗
Figure 28
Figure 28. Figure 28: The GHZ (Green) as a function of radial distance from the galactic center (GC) and time before the present for the Milky Way Galaxy. The left model is for complex life, for which it assumes life requires 4 ± 1 Gyr to form, while the right model considers all life. The green curve on the right of the left figure is the age distribution of complex life, and in the right figure the age distribution of all li… view at source ↗
Figure 29
Figure 29. Figure 29: Galaxies display astrophysical correlations: the Tully-Fisher for spiral galaxies (left) and the Faber-Jackson for elliptical galaxies (right). galactic Type-III civilization. Ambitious technological life, life that seeks to maximize resource availability, has been proposed as motivation for the existence of multi-galactic civilizations (Olson 2017). All it takes is for a single civilization across hundre… view at source ↗
Figure 30
Figure 30. Figure 30: A spacetime diagram of the emergence of ambitious (A1, A2) and non-ambitious civilizations (C1, C2, C3). The horizontal direction represents space, and the vertical time; light cones are represented in yellow. times that of the Moon in the sky! The typical distance to such bubbles is billion light years, making these intergalactic civilizations both incredibly large, close to Type-IV, and incredibly far a… view at source ↗
Figure 31
Figure 31. Figure 31: Synergies between bio- and techno- signatures overlap for targets at the Earth, solar system and exoplanet scales (in red). Technosignatures searches extend beyond these scales where they have different synergies with astronomy, astrophysics or engineering (in black). 9. DISCUSSION 9.1. Biosignatures and technosignatures The frontier between biosignatures and technosignatures may be fuzzy. If we detect a … view at source ↗
Figure 32
Figure 32. Figure 32: Schema of an anomaly-driven search for technosignatures. This method helps to identify SETI candidates, but also to detect and study extreme natural objects, between a defined upper-limit and an anomaly threshold. As such, it naturally produces ancillary science, even if no ETI is found. Figure from (Lazio et al. 2023). in combination with other measurements, can help to assess the degree of thermal diseq… view at source ↗
Figure 33
Figure 33. Figure 33: Axes of merit for technosignature searches, from (Sheikh 2020). Note that axes 1–4 (in orange) cover the more practical aspects of any technosignature searches (Sheikh 2020). We note that other assessment scales have been proposed to rank potential biosignatures (Neveu et al. 2018; Green 2021; Meadows et al. 2022). However, further work is needed to create an encompassing framework for assessing and compa… view at source ↗
Figure 34
Figure 34. Figure 34: Ichnoscale (relative footprint of a given technosignature in units of current Earth technology) vs. number of targets for several possible technosignatures. Filled (empty) circles represent continuous (discontinuous) observables. Figure from Socas-Navarro et al. (2021). production is outside it: all the objects that only exist thanks to human intervention within nature. We find in his distinction between … view at source ↗
Figure 35
Figure 35. Figure 35: The “Wow” signal recorded on August 15, 1977 at the Big Ear Ohio State Radio Observatory, immortalized by Jerry Ehman’s annotation upon reviewing the data (Charbonneau 2018) education and outreach to draw people of all ages towards science. Epistemology Most technosignatures reviewed here involve observing remotely with the help of astronomical instruments. Instruments like telescopes do not retrieve info… view at source ↗
read the original abstract

This paper aims to review the diverse range of technosignatures that have been proposed in the literature. We organize the review by scales, starting carefully from Earth, then zooming out to Earth's orbit, the solar system, including the Moon, the Earth-Moon Lagrange points, the inner solar system, the asteroid belt, interstellar objects, the outer solar system, the Kuiper belt, the solar gravitational lens region, and the Oort cloud. We then introduce the Kardashev and Barrow scale before exploring exoplanetary technosignatures, from surface, atmospheric to orbital sources. We next consider stellar technosignatures that may involve massive energy utilization, stellar modification or stellar pollution, and end with a section about compact objects. We then review attempts to detect interstellar communication, and discuss many dimensions of the search space from first principles. Then we consider interstellar travel technosignatures, and end with galactic, extragalactic and universal signatures. We end with a discussion about synergies between biosignatures and technosignatures searches, anomaly detection, multimodal strategies, instruments for detecting technosignatures, how to evaluate and prioritize the search, as well as epistemological issues.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 2 minor

Summary. The paper reviews the diverse range of technosignatures proposed in the literature, organizing them by spatial scales from Earth through the solar system, exoplanets, stars, compact objects, interstellar communication and travel, to galactic and universal levels. It also covers synergies with biosignatures, anomaly detection, multimodal strategies, instruments, prioritization, and epistemological issues.

Significance. If the cited literature is representative and the scale-based taxonomy proves useful for guiding searches, this review could serve as a helpful reference for organizing and prioritizing technosignature efforts in astrobiology and SETI. The explicit framing as a survey rather than new empirical work, combined with discussion of detection strategies and synergies, adds practical value for future observational planning.

major comments (1)
  1. [Abstract and overall structure] The central organizing principle (spatial scales from Earth to galactic) is presented as a logical framework in the abstract and structure description, but the manuscript does not include an explicit comparison to alternative taxonomies such as energy-based (Kardashev/Barrow) or detection-method-based classifications; this weakens the justification for why the chosen structure best serves the goal of comprehensive coverage.
minor comments (2)
  1. [Exoplanetary and stellar sections] In the sections on exoplanetary and stellar technosignatures, ensure that all cited works are accompanied by brief context on their observational feasibility or current search status to aid readers unfamiliar with the subfield.
  2. [Synergies and strategies discussion] The discussion of synergies between biosignatures and technosignatures would benefit from a short table or bullet list summarizing overlapping observables and instruments, to improve clarity and utility.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the positive assessment of the manuscript and the recommendation for minor revision. We address the single major comment below and will incorporate changes to strengthen the justification for our organizational framework.

read point-by-point responses

  1. Referee: [Abstract and overall structure] The central organizing principle (spatial scales from Earth to galactic) is presented as a logical framework in the abstract and structure description, but the manuscript does not include an explicit comparison to alternative taxonomies such as energy-based (Kardashev/Barrow) or detection-method-based classifications; this weakens the justification for why the chosen structure best serves the goal of comprehensive coverage.

    Authors: We agree that an explicit comparison to alternative taxonomies would improve the justification for the spatial-scale organization. Although the manuscript already introduces the Kardashev and Barrow scales prior to the exoplanet discussion, we did not provide a direct side-by-side evaluation against our chosen framework or against detection-method-based alternatives. In the revised manuscript we will add a concise subsection early in the introduction that contrasts the spatial-scale approach with energy-based (Kardashev/Barrow) and detection-method classifications. We will note that energy scales emphasize technological capability independent of distance, while our organization aligns more directly with observational accessibility, instrumental requirements, and the practical progression of searches from nearby to cosmic distances. This addition will clarify the rationale for comprehensive coverage without altering the overall structure. revision: yes

Circularity Check

0 steps flagged

No significant circularity: descriptive review of external literature

full rationale

The paper is a survey that compiles and organizes technosignature proposals from the cited literature by spatial scales (Earth to galactic), covering synergies with biosignatures and detection strategies. It introduces no new equations, derivations, predictions, or parameter fits. All content reduces to external references rather than self-referential steps, self-citations as load-bearing premises, or renamings of internal results. The scale-based taxonomy is presented as an organizing framework, not a derived claim. This matches the default expectation of no circularity for self-contained reviews against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

This is a review paper that surveys existing literature on technosignatures. It introduces no new free parameters, axioms, or invented entities of its own; all content draws from cited prior work without adding original postulates or fittings.

pith-pipeline@v0.9.0 · 5846 in / 1224 out tokens · 39888 ms · 2026-05-21T01:57:55.467143+00:00 · methodology

discussion (0)

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Reference graph

Works this paper leans on

14 extracted references · 14 canonical work pages · 1 internal anchor

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