Technosignature or technomarker is any measurable property or effect that provides scientific evidence of past or present technology. Technosignatures are analogous to biosignatures, which signal the presence of life, whether intelligent or not. Some authors prefer to exclude radio transmissions from the definition, but such restrictive usage is not widespread. Jill Tarter has proposed that the search for extraterrestrial intelligence (SETI) be renamed "the search for technosignatures". Various types of technosignatures, such as radiation leakage from megascale astroengineering installations such as Dyson spheres, the light from an extraterrestrial ecumenopolis, or Shkadov thrusters with the power to alter the orbits of stars around the Galactic Center, may be detectable with hypertelescopes. Some examples of technosignatures are described in Paul Davies's 2010 book The Eerie Silence, although the terms "technosignature" and "technomarker" do not appear in the book.
Illustration of various types of technosignatures.
Lights from cities and infrastructure on Earth at night from space
Artist's illustration of an advanced ET civilization with industrial pollution
The IKAROS light sail of 2010
A biosignature is any substance – such as an element, isotope, molecule, or phenomenon – that provides scientific evidence of past or present life on a planet. Measurable attributes of life include its complex physical or chemical structures, its use of free energy, and the production of biomass and wastes.
Electron micrograph of microfossils from a sediment core obtained by the Deep Sea Drilling Program
Some researchers suggested that these microscopic structures on the Martian ALH84001 meteorite could be fossilized bacteria.
An image of the plumes of water and ice coming from the surface of Enceladus. Future missions will investigate these geysers to determine the composition and look for signs of life.
