Temporally and spatially enduring technological extrasolar civilizations modify their environment in detectable and unambiguous ways (e.g., technosignatures).

Advanced civilizations in disequilibrium with their supporting environment.

Enduring technological extrasolar civilizations modify their environment in detectable but non-unique ways; if at all.

Geological and astronomical phenomena and civilizations in equilibrium with their environment.
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Alexander Sessa   Subscribe ...


Detection of communication technosignatures


Radio emissions from an exoplanet can serve as an indicator for the presence of an advanced civilization.

eLow-frequency radio observatories covering a range of 80-300 MHz could be used to detect Earth-like telecommunication leakage from extrasolar planets (i.e., eavesdrop), which would appear as a series of narrow spectral lines unattributable to known atomic or molecular lines.

Detection of atmospheric technosignatures


Atmospherically present pollutants can be a strong indicator of industrial-like activity occurring on an exoplanet’s surface.

eThe James Webb Space Telescope (JWST) will be capable of resolving atmospheric tetrafluoromethane (CF4) and trichlorofluoromethane (CCl3F) absorptions in the mid-infrared transmission spectra of transiting exoplanets.


Gases associated with industrial activity can be produced naturally.

eAtmospheric sulfur hexafluoride (SF6) can be released into the environment via geologic means (i.e., via fracturing of silicic igneous rocks (due to faulting) and hydrothermal springs driven by volcanic activity).

eAtmospheric tetrafluoromethane (CF4) can be released into the environment via geologic means (i.e., via surface weathering, metamorphism or metasomatism, and continuous diffusion of gas at depth of continental crust).


Natural nuclear reactors and artificial ground-based nuclear fission-related activities can affect a terrestrial planet’s atmospheric environment in analogous ways.

eWhen functioning, the Oklo natural nuclear reactor was believed to be similar to past nuclear disasters (e.g., Three Mile Island, Chernobyl, and Fukushima Daiichi incidents) in terms of fission by-products released into the environment and resulting atmospheric anomalies; today, the areas surrounding the fossil reactors still produce fission products that influence the near atmospheric environment.

Detection of structural technosignatures


Anomalous, and/or excess, radiation emanating from an exoplanet’s surface can indicate the presence of an advanced civilization.

eNear-term, surface- [the European Extremely Large Telescope (EELT), the Giant Magellan Telescope (GMT), and the Thirty Meter Telescope (TMT)] and space-based telescopes [the James Webb Space Telescope (JWST), Darwin, and Terrestrial Planet Finder (TPF)] will be capable of searching for artificially illuminated extrasolar planets by observing the orbital phase (time) modulation of incident flux from the illumination of the nightside of these planets as they orbit their primary.

eThe temporal and spatial distribution of excess thermal radiation (i.e., waste heat) emanating from a structured, technological extrasolar species could be detected using the photometric capabilities of 70-meter class or larger telescopes (e.g., the concept Colossus telescope).


Natural materials readily interact with incident radiation on a cosmic scale.

eThe photometric properties of astrophysical (or interstellar) dust, (e.g., brightness and color temperature) can mimic those of high-luminosity waste heat.

Detection of planet-scale technosignatures


If employed, sustainable technologies such as solar panels could be detection on an exoplanet’s surface.

eSurface-based, mega-scale photovoltaic arrays constructed of readily available materials such as silicon, which has a characteristic “artificial edge” present in the UV spectral region, could be detected via the reflectance spectroscopic capabilities of future telescopes, such as Wide Field Infrared Survey Telescope (WFIRST), Large UV/Optical/Infrared Surveyor (LUVOIR), Habitable Exoplanet Imaging Mission (HabEx), and High-Definition Space Telescope (HDST).


Assuming the sustainability solution to the Fermi Paradox holds, a civilization should become more sustainable and therefore less detectable as it becomes more advanced.

eIt is hypothesized that most civilizations manage their growth as to follow the same trajectory of humans (i.e., slowdown population growth and energy consumption) and eventually would be in equilibrium with the exoplanet they inhabit (i.e., indistinguishable from an uninhabited world) or go extinct.