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Technosignature or technomarker is any measurable property or effect that provides
scientific evidence Scientific evidence is evidence that serves to either support or counter a scientific theory or hypothesis, although scientists also use evidence in other ways, such as when applying theories to practical problems. "Discussions about empirical ev ...
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 Jill Cornell Tarter (born January 16, 1944) is an American astronomer best known for her work on the search for extraterrestrial intelligence ( SETI). Tarter is the former director of the Center for SETI Research, holding the Bernard M. Oliver ...
has proposed that the
search for extraterrestrial intelligence The search for extraterrestrial intelligence (SETI) is a collective term for scientific searches for intelligent extraterrestrial life, for example, monitoring electromagnetic radiation for signs of transmissions from civilizations on other ...
(SETI) be renamed "the search for technosignatures". Various types of technosignatures, such as radiation leakage from megascale astroengineering installations such as
Dyson sphere A Dyson sphere is a hypothetical megastructure that completely encompasses a star and captures a large percentage of its solar power output. The concept is a thought experiment that attempts to explain how a spacefaring civilization would meet ...
s, the light from an extraterrestrial ecumenopolis, or Shkadov thrusters with the power to alter the orbits of stars around the
Galactic Center The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact ra ...
, may be detectable with hypertelescopes. Some examples of technosignatures are described in
Paul Davies Paul Charles William Davies (born 22 April 1946) is an English physicist, writer and broadcaster, a professor in Arizona State University and Director of BEYOND: Center for Fundamental Concepts in Science. He is affiliated with the Institute ...
's 2010 book '' The Eerie Silence'', although the terms "technosignature" and "technomarker" do not appear in the book.


Astroengineering projects

A
Dyson sphere A Dyson sphere is a hypothetical megastructure that completely encompasses a star and captures a large percentage of its solar power output. The concept is a thought experiment that attempts to explain how a spacefaring civilization would meet ...
, constructed by life forms dwelling in proximity to a Sun-like star, would cause an increase in the amount of infrared radiation in the star system's emitted spectrum. Hence,
Freeman Dyson Freeman John Dyson (15 December 1923 – 28 February 2020) was an English-American theoretical physicist and mathematician known for his works in quantum field theory, astrophysics, random matrices, mathematical formulation of quantum m ...
selected the title "Search for Artificial Stellar Sources of Infrared Radiation" for his 1960 paper on the subject. SETI has adopted these assumptions in its search, looking for such "infrared heavy" spectra from
solar analog Solar-type star, solar analogs (also analogues), and solar twins are stars that are particularly similar to the Sun. The stellar classification is a hierarchy with solar twin being most like the Sun followed by solar analog and then solar-type ...
s. Since 2005,
Fermilab Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a United States Department of Energy national laboratory specializing in high-energy particle physics. Since 2007, Fermilab has been oper ...
has conducted an ongoing survey for such spectra, analyzing data from the Infrared Astronomical Satellite. Identifying one of the many infra-red sources as a Dyson sphere would require improved techniques for discriminating between a Dyson sphere and natural sources. Fermilab discovered 17 "ambiguous" candidates, of which four have been named "amusing but still questionable". Other searches also resulted in several candidates, which remain unconfirmed. In October 2012, astronomer Geoff Marcy, one of the pioneers of the search for
extrasolar planets An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, in ...
, was given a research grant to search data from the ''
Kepler Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws o ...
'' telescope, with the aim of detecting possible signs of Dyson spheres.


Orbital paths, transit signatures, stellar activity and star-system composition

Shkadov thrusters, with the hypothetical ability to change the orbital paths of stars in order to avoid various dangers to life such as cold molecular clouds or cometary impacts, would also be detectable in a similar fashion to the transiting extrasolar planets searched by ''Kepler''. Unlike planets, though, the thrusters would appear to abruptly stop over the surface of a star rather than crossing it completely, revealing their technological origin. In addition, evidence of targeted extrasolar
asteroid mining Asteroid mining is the hypothetical exploitation of materials from asteroids and other minor planets, including near-Earth objects. Notable asteroid mining challenges include the high cost of spaceflight, unreliable identification of asteroids ...
may also reveal
extraterrestrial intelligence Extraterrestrial intelligence (often abbreviated ETI) refers to hypothetical intelligent extraterrestrial life. The question of whether other inhabited worlds might exist has been debated since ancient times. The modern form of the concept emerged ...
(ETI). Furthermore, it has been suggested that information could be hidden within the transit signatures of other planets. Advanced civilizations could "cloak their presence, or deliberately broadcast it, through controlled laser emission". Other characteristics proposed as potential technosignatures (or starting points for detection of clearer signatures) include peculiar
orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting pla ...
s such as arranging planets in prime number patterns. Coronal and
chromospheric A chromosphere ("sphere of color") is the second layer of a star's atmosphere, located above the photosphere and below the solar transition region and corona. The term usually refers to the Sun's chromosphere, but not exclusively. In the S ...
activity on stars might be altered. Extraterrestrial civilizations may use free-floating planets (
rogue planet A rogue planet (also termed a free-floating planet (FFP), interstellar, nomad, orphan, starless, unbound or wandering planet) is an interstellar object of planetary-mass, therefore smaller than fusors (stars and brown dwarfs) and without a h ...
s) for interstellar transportation with a number of proposed possible technosignatures.


Communication networks

A study suggests that if ETs exist, they may have established communications network(s) and may already have probes in the solar system whose communication may be detectable. Studies by John Gertz suggest flyby (scout) probes might intermittently surveil nascent solar systems and permanent probes would communicate with a home base, potentially using triggers and conditions such as detection of electromagnetic leakage or biosignatures. They also suggest several strategies to detecting local ET probes such as detecting emitted optical messages. He also finds that due to interstellar networks of communications nodes, the search for deliberate interstellar signals – as is common in SETI – may be futile. The architecture may consist of nodes separated by sub-light-year distances and strung out between neighboring stars. It may also contain pulsars as
beacon A beacon is an intentionally conspicuous device designed to attract attention to a specific location. A common example is the lighthouse, which draws attention to a fixed point that can be used to navigate around obstacles or into port. More mode ...
s or nodes whose beams are modulated by mechanisms that could be searched for. Moreover, a study suggests prior searches wouldn't have detected cost-effective electromagnetic signal beacons.


Planetary analysis


Artificial heat and light

Various astronomers, including Avi Loeb of the Center for Astrophysics Harvard & Smithsonian and Edwin L. Turner of
Princeton University Princeton University is a private research university in Princeton, New Jersey. Founded in 1746 in Elizabeth as the College of New Jersey, Princeton is the fourth-oldest institution of higher education in the United States and one of the ...
have proposed that artificial light from extraterrestrial planets, such as that originating from cities, industries, and transport networks, could be detected and signal the presence of an advanced civilization. Such approaches, though, make the assumption that the
radiant energy Radiant may refer to: Computers, software, and video games * Radiant (software), a content management system * GtkRadiant, a level editor created by id Software for their games * Radiant AI, a technology developed by Bethesda Softworks for ''Th ...
generated by civilization would be relatively clustered and can therefore be detected easily. Light and heat detected from planets must be distinguished from natural sources to conclusively prove the existence of intelligent life on a planet. For example, NASA's 2012 ''Black Marble'' experiment showed that significant stable light and heat sources on Earth, such as chronic wildfires in arid
Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to t ...
, originate from uninhabited areas and are naturally occurring. The proposed LUVOIR A may be able to detect city lights twelve times those of Earth on Proxima b in 300 hours.


Atmospheric analysis

Atmospheric analysis of planetary atmospheres, as is already done on various Solar System bodies and in a rudimentary fashion on several
hot Jupiter Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods (). The close proximity to their stars and high surface-atmosphere t ...
extrasolar planets, may reveal the presence of chemicals produced by technological civilizations. For example, atmospheric emissions from human technology use on Earth, including
nitrogen dioxide Nitrogen dioxide is a chemical compound with the formula . It is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year for use primarily in the productio ...
and
chlorofluorocarbon Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F), produced as volatile derivatives of methane, ethane, and p ...
s, are detectable from space. Artificial air pollution may therefore be detectable on extrasolar planets and on Earth via "atmospheric SETI" – including NO2 pollution levels and with telescopic technology close to today. Such technosignatures may consist not of the detection of the level of one specific chemical but simultaneous detections of levels of multiple specific chemicals in atmospheres. However, there remains a possibility of mis-detection; for example, the
atmosphere of Titan The atmosphere of Titan is the dense layer of gases surrounding Titan, the largest moon of Saturn. It is the only thick atmosphere of a natural satellite in the Solar System. Titan's lower atmosphere is primarily composed of nitrogen (94.2%), ...
has detectable signatures of complex chemicals that are similar to what on Earth are industrial pollutants, though not the byproduct of civilisation. Some SETI scientists have proposed searching for artificial atmospheres created by planetary engineering to produce habitable environments for colonisation by an ETI.


Extraterrestrial artifacts, influence and spacecraft


Spacecraft

Interstellar spacecraft A starship, starcraft, or interstellar spacecraft is a theoretical spacecraft designed for traveling between planetary systems. The term is mostly found in science fiction. Reference to a "star-ship" appears as early as 1882 in '' Oahspe: A N ...
may be detectable from hundreds to thousands of
light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distance, astronomical distances and is equivalent to about 9.46 Orders of magnitude (numbers)#1012, trillion kilometers (), or 5.88  ...
s away through various forms of radiation, such as the
photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they alwa ...
s emitted by an
antimatter rocket An antimatter rocket is a proposed class of rockets that use antimatter as their power source. There are several designs that attempt to accomplish this goal. The advantage to this class of rocket is that a large fraction of the rest mass of ...
or
cyclotron radiation Cyclotron radiation is electromagnetic radiation emitted by non-relativistic accelerating charged particles deflected by a magnetic field. The Lorentz force on the particles acts perpendicular to both the magnetic field lines and the particles' mot ...
from the interaction of a magnetic sail with the
interstellar medium In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...
. Such a signal would be easily distinguishable from a natural signal and could hence firmly establish the existence of extraterrestrial life, were it to be detected. In addition, smaller
Bracewell probe A Bracewell probe is a hypothetical concept for an autonomous interstellar space probe dispatched for the express purpose of communication with one or more alien civilizations. It was proposed by Ronald N. Bracewell in a 1960 paper, as an alter ...
s within the Solar System itself may also be detectable by means of optical or radio searches.
Self-replicating spacecraft The concept of Self-replicating spacecraft, as envisioned by mathematician John von Neumann, has been described by futurists including physicist Michio Kaku and discussed across a wide breadth of hard science fiction novels and stories. Self-rep ...
or their communications networks could potentially be detectable within our Solar system or in nearby star-based systems, if they are located there. Such technologies or their footprints could be in Earth's orbit, on the Moon or on the Earth.


Satellites

A less advanced technology, and one closer to humanity's current technological level, is the Clarke Exobelt proposed by Astrophysicist Hector Socas-Navarro of the Instituto de Astrofisica de Canarias. This hypothetical belt would be formed by all the artificial
satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...
s occupying
geostationary A geostationary orbit, also referred to as a geosynchronous equatorial orbit''Geostationary orbit'' and ''Geosynchronous (equatorial) orbit'' are used somewhat interchangeably in sources. (GEO), is a circular geosynchronous orbit in altitud ...
/
geosynchronous A geosynchronous orbit (sometimes abbreviated GSO) is an Earth-centered orbit with an orbital period that matches Earth's rotation on its axis, 23 hours, 56 minutes, and 4 seconds (one sidereal day). The synchronization of rotation and orbital ...
orbits around an
exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...
. From early simulations it appeared that a very dense satellite belt, requiring only a moderately more-advanced civilization than ours, would be detectable with existing technology in the light curves from transiting exoplanets, but subsequent analysis has questioned this result, suggesting that exobelts detectable by current and upcoming missions will be very rare.


Extraterrestrial influence or activity on Earth

It has been suggested that once extraterrestrials arrive "at a new home, such life will almost certainly create technosignatures (because it used technology to get there), and some fraction of them may also eventually give rise to a new biosphere". Microorganism DNA may have been used for self-replicating messages. See also:
DNA digital data storage DNA digital data storage is the process of encoding and decoding binary data to and from synthesized strands of DNA. While DNA as a storage medium has enormous potential because of its high storage density, its practical use is currently severely ...


On exoplanets

Low- or high-albedo installations such as solar panels may also be detectable, albeit distinguishing artificial megastructures from high- and low-albedo natural environments (e.g., bright ice caps) may make it unfeasible.


Scientific projects searching for technosignatures

One of the first attempts to search for Dyson Spheres was made by Vyacheslav Slysh from the Russian Space Research Institute in Moscow in 1985 using data from the Infrared Astronomical Satellite (IRAS). Another search for technosignatures, circa 2001, involved an analysis of data from the
Compton Gamma Ray Observatory The Compton Gamma Ray Observatory (CGRO) was a space observatory detecting photons with photon energy, energies from 20 kElectronvolt#Properties, eV to 30 GeV, in Earth orbit from 1991 to 2000. The observatory featured four main tele ...
for traces of anti-matter, which, besides one "intriguing spectrum probably not related to SETI", came up empty. In 2005,
Fermilab Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a United States Department of Energy national laboratory specializing in high-energy particle physics. Since 2007, Fermilab has been oper ...
had an ongoing survey for such spectra by analyzing data from IRAS. Identifying one of the many infra-red sources as a Dyson Sphere would require improved techniques for discriminating between a Dyson Sphere and natural sources. Fermilab discovered 17 potential "ambiguous" candidates of which four have been named "amusing but still questionable". Other searches also resulted in several candidates, which are, however, unconfirmed. In a 2005 paper, Luc Arnold proposed a means of detecting planetary-sized artifacts from their distinctive transit light curve signature. He showed that such technosignature was within the reach of space missions aimed at detecting exoplanets by the
transit method Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. In addition to the intrinsic difficulty o ...
, as were ''Corot'' or ''Kepler'' projects at that time. The principle of the detection remains applicable for future exoplanets missions. In 2012, a trio of astronomers led by Jason Wright started a two-year search for Dyson Spheres, aided by grants from the
Templeton Foundation The John Templeton Foundation (Templeton Foundation) is a Philanthropy, philanthropic organization that reflects the ideas of its founder, John Templeton, who became wealthy via a career as a Contrarian investing, contrarian investor, and wanted ...
. In 2013, Geoff Marcy received funding to use data from the Kepler Telescope to search for Dyson Spheres and interstellar communication using lasers, and Lucianne Walkowicz received funding to detect artificial signatures in stellar photometry. Starting in 2016, astronomer
Jean-Luc Margot Jean-Luc Margot (born 1969) is a Belgian-born astronomer and a UCLA professor who specializes in planetary sciences. Career Margot has discovered and studied several binary asteroids with radar and optical telescopes. His discoveries include ( ...
of
UCLA The University of California, Los Angeles (UCLA) is a public land-grant research university in Los Angeles, California. UCLA's academic roots were established in 1881 as a teachers college then known as the southern branch of the California ...
has been searching for technosignatures with large radio telescopes.


Vanishing stars

In 2016, it was proposed that vanishing stars are a plausible technosignature. A pilot project searching for vanishing stars was carried out, finding one candidate object. In 2019, the Vanishing & Appearing Sources during a Century of Observations (VASCO) project began more general searches for vanishing and appearing stars, and other astrophysical transients They identified 100 red transients of "most likely natural origin", while analyzing 15% of the image data. In 2020, the VASCO collaboration started up a citizen science project, vetting through images of many thousands of candidate objects. The citizen science project is carried out in close collaboration with schools and amateur associations mainly in African countries. The VASCO project has been referred to as "Perhaps the most general artefact search to date". In 2021, VASCO's principal investigator Beatriz Villarroel received a L'Oreal-Unesco prize in Sweden for the project. In June 2021, the collaboration published the discovery of nine light sources seemingly appearing and vanishing simultaneously in the sky. No natural phenomena can explain the presence of the objects in an old photographic plate from 1950. The group carefully indicated that either nuclear fallout from unlisted atomic bombs contaminated the plates or that a new celestial phenomenon might be behind. For example, the high spatial density of transients is caused by the presence of artificial, reflective objects at high orbits around Earth in 1950. Continued studies, are bringing more support for the authenticity of the phenomenon with multiple transients. See also: Diminished Reality (the reverse of
augmented reality Augmented reality (AR) is an interactive experience that combines the real world and computer-generated content. The content can span multiple sensory modalities, including visual, auditory, haptic, somatosensory and olfactory. AR can be de ...
).


Organization of novel projects

In June 2020, NASA was awarded their first
SETI The search for extraterrestrial intelligence (SETI) is a collective term for scientific searches for intelligent extraterrestrial life, for example, monitoring electromagnetic radiation for signs of transmissions from civilizations on other pl ...
-specific grant in three decades. The grant funds the first NASA-funded search for technosignatures from advanced extraterrestrial civilizations other than radio waves, including the creation and population of an online technosignature
library A library is a collection of materials, books or media that are accessible for use and not just for display purposes. A library provides physical (hard copies) or digital access (soft copies) materials, and may be a physical location or a vi ...
. A 2021
scientific review A review article is an article that summarizes the current state of understanding on a topic within a certain discipline. A review article is generally considered a secondary source since it may analyze and discuss the method and conclusions i ...
produced by the i.a. NASA-sponsored online workshop ''TechnoClimes 2020'' classified possible optimal mission concepts for the search of technosignatures. It evaluates signatures based on a metric about the distance of humanity to the capacity of developing the signature's required technology – a comparison to contemporary human technology footprints, associated methods of detection and ancillary benefits of their search for other astronomy. The study's conclusions include a robust rationale for organizing missions for searching artifacts – including probes – within the Solar system. Available unde
CC BY 4.0
on arXiv.
In 2021, astronomers proposed a sequence of "verification checks for narrowband technosignature signals" after concluding that technosignature candidate BLC1 could be the result of a form of local radiofrequency interference. It has been suggested that observatories on the Moon could be more successful. In 2022, scientists provided an overview of the capabilities of ongoing, recent, past, planned and proposed missions and observatories for detecting various alien technosignatures.


Implications of detection

Steven J. Dick states that there generally are no principles for dealing with successful SETI detections. Detections of technosignatures may have ethical implications, such as conveying information related to astroethical and related machine ethics ones (e.g. related to machines' applied ethical
values In ethics and social sciences, value denotes the degree of importance of something or action, with the aim of determining which actions are best to do or what way is best to live (normative ethics in ethics), or to describe the significance of di ...
), or include information about alien
societies A society is a group of individuals involved in persistent social interaction, or a large social group sharing the same spatial or social territory, typically subject to the same political authority and dominant cultural expectations. Societ ...
or histories or fates, which may vary depending on the type, prevalence and form of the detected signature's technology. Moreover, various types of information about detected technosignatures and their distribution or dissemination may have varying implications that may also depend on time and context.


See also

* Laser SETI *
UFO Report (U.S. Intelligence) ''Preliminary Assessment: Unidentified Aerial Phenomena'', also known as the UAP Report and colloquially misnamed the Pentagon UFO Report, is a United States federally mandated assessment, prepared and published by the Office of the Director of Na ...


Further reading

*


References

{{Extraterrestrial life Extraterrestrial life Astrobiology * Technology