Technosignature

A technosignature is any observable signature of technology — radio emission, optical pulse, waste heat, atmospheric pollutant, megastructure transit dip — that would, if detected, constitute evidence of a technological civilization elsewhere in the universe. The term is the technological analogue to biosignature (an observable signature of biology, such as the disequilibrium chemistry produced by photosynthesis), and it is the working concept behind modern SETI — the Search for Extraterrestrial Intelligence.

Origin of the term

The word technosignature was popularized by astronomer Jill Tarter in the late 2000s and entered formal NASA usage following a 2018 technosignatures workshop hosted by the Lyndon B. Johnson Space Center. The framing deliberately broadens the historical SETI emphasis on narrow-band radio emission to include any technologically produced observable: the search is for evidence of technology, not specifically of signals beamed at us.

NASA’s Astrophysics Division formally funded technosignature research beginning in fiscal year 2018, with the Penn State Extraterrestrial Intelligence Center and the Breakthrough Listen initiative — based at the University of California, Berkeley — now anchoring the field’s contemporary research program.

Categories of technosignature

Technosignatures are organized by the physical channel in which they would be observed:

• Radio technosignatures — narrow-band, continuously emitted, or pulsed radio signals inconsistent with natural astrophysical sources. The historical core of SETI, conducted at facilities including the Allen Telescope Array (Hat Creek, California), the Green Bank Telescope (West Virginia), and the now-collapsed Arecibo Observatory.
• Optical and infrared technosignatures — laser pulses (optical SETI), or anomalous infrared excess from a star, which would be consistent with a partial or full Dyson structure absorbing stellar radiation and re-radiating it as waste heat.
• Atmospheric technosignatures — industrial pollutants such as chlorofluorocarbons or nitrogen dioxide detected in the spectrum of an exoplanet atmosphere. The James Webb Space Telescope’s transmission spectroscopy capabilities are the first to make this channel observationally accessible.
• Megastructure technosignatures — irregular transit dips consistent with a non-spherical occulting structure, of the kind briefly hypothesized for the 2015 light-curve anomalies of the star KIC 8462852 (“Tabby’s Star”).
• Artefactual technosignatures — physical objects within our own solar system that exhibit non-natural properties. The Bracewell probe hypothesis (see related entry) is the canonical example.

Distinction from biosignature

A biosignature is evidence of life of any kind, including microbial. A technosignature is specifically evidence of life that has produced detectable technology. The two categories are not redundant: a planet could exhibit biosignatures without technosignatures (Earth for most of its history), and in principle a technosignature could be detected from a civilization whose biology is no longer extant — an artefact outliving its makers.

Negative results matter

A central methodological point: a null technosignature result is a real result. Reporting that a target was scanned, at specified frequencies and durations, with no detection, narrows the parameter space of where and how a civilization could be transmitting. The widely cited Drake equation depends on terms — particularly f_c, the fraction of intelligent civilizations producing detectable technology — that can only be constrained empirically by accumulated technosignature surveys, including the negative ones.

The June 2026 scan of 3I/ATLAS by the SETI Institute using the Allen Telescope Array — more than seven hours of observation, no candidate signals surviving terrestrial-source rejection — is documented in the Council archive as a clean negative result of this kind. It does not prove the absence of technology aboard the object; it does establish that, within the frequency range and duration scanned, no signal was emitted strong enough to register above the noise floor.

Council position

The Council treats technosignature research as a structured scientific programme of the same epistemic standing as exoplanet characterization or biosignature search. We report positive detections, when they occur, as we would any peer-reviewed astronomical finding, and we report nulls as nulls — neither as proof of absence nor as evidence of suppression.