Property that provides scientific evidence for the presence of technology
Illustration of various types of technosignatures.
Technosignature ortechnomarker is any measurable property or effect that providesscientific evidence of past orpresent technology.[1][2] Technosignatures are analogous tobiosignatures, which signal the presence of life, whether intelligent or not.[1][3] Some authors prefer to exclude radio transmissions from the definition,[4] but such restrictive usage is not widespread.Jill Tarter has proposed that thesearch for extraterrestrial intelligence (SETI) be renamed "the search for technosignatures".[1] Various types of technosignatures, such as radiation leakage frommegascaleastroengineering installations such asDyson spheres, the light from an extraterrestrialecumenopolis, orShkadov thrusters with the power to alter the orbits of stars around theGalactic Center, may be detectable withhypertelescopes. Some examples of technosignatures are described inPaul Davies's 2010 bookThe Eerie Silence, although the terms "technosignature" and "technomarker" do not appear in the book.
In February 2023, astronomers reported, after scanning 820 stars, the detection of 8 possible technosignatures for follow-up studies.[5]
ADyson sphere, one of the best-known speculative technologies that may generate a technosignature
ADyson sphere, constructed by life forms dwelling in proximity to aSun-like star, would cause an increase in the amount of infrared radiation in the star system's emitted spectrum. Hence,Freeman Dyson selected the title "Search for Artificial Stellar Sources of Infrared Radiation" for his 1960 paper on the subject.[6] SETI has adopted these assumptions in its search, looking for such "infrared heavy" spectra fromsolar analogs. Since 2005,Fermilab has conducted an ongoing survey for such spectra, analyzing data from theInfrared Astronomical Satellite.[7][8]
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.[9] Fermilab discovered 17 "ambiguous" candidates, of which four have been named "amusing but still questionable".[10] Other searches also resulted in several candidates, which remain unconfirmed.[7] In October 2012, astronomerGeoff Marcy, one of the pioneers of the search forextrasolar planets, was given a research grant to search data from theKepler telescope, with the aim of detecting possible signs of Dyson spheres.[11]
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 ascold molecular clouds orcometary impacts, would also be detectable in a similar fashion to thetransiting extrasolar planets searched byKepler. 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.[12] In addition, evidence of targeted extrasolarasteroid mining may also revealextraterrestrial intelligence (ETI).[13] Furthermore, it has been suggested that information could be hidden within the transit signatures of other planets.[14] Advanced civilizations could "cloak their presence, or deliberately broadcast it, through controlled laser emission".[15] Other characteristics proposed as potential technosignatures (or starting points for detection of clearer signatures) include peculiarorbital periods such as arranging planets in prime number patterns.[16][17][18] Coronal andchromospheric activity on stars might be altered.[19] Extraterrestrial civilizations may use free-floating planets (rogue planets) for interstellar transportation with a number of proposed possible technosignatures.[20]
A study suggests that if ETs exist, they may have established communications network(s) and may already have probes in theSolar System whose communication may be detectable.[21] Studies by John Gertz suggest flyby (scout)[22] probes might intermittently surveil nascent planetary systems and permanent probes would communicate with a home base, potentially using triggers and conditions such as detection of electromagnetic leakage or biosignatures.[23] They also suggest several strategies to detecting local ET probes[24] such as detecting emitted optical messages.[25] He also finds that due to interstellar networks of communications nodes, the search for deliberate interstellar signals – as is common in SETI[26] – may be futile.[27] The architecture may consist of nodes separated by sub-light-year distances and strung out between neighboring stars.[28] It may also contain pulsars asbeacons[29] or nodes whose beams are modulated by mechanisms that could be searched for.[30] Moreover, a study suggests prior searches wouldn't have detected cost-effective electromagnetic signal beacons.[31]
Light and heat detected from planets must be distinguished from natural sources to conclusively prove the existence of intelligent life on a planet.[4] For example, NASA's 2012Black Marble experiment showed that significant stable light and heat sources on Earth, such as chronic wildfires in aridWestern Australia, originate from uninhabited areas and are naturally occurring.[32]
Spectroscopic observations of exoplanet nightsides would be able to identify artificial lighting via its distinct spectroscopic signature. Work by astronomerThomas Beatty has shown that the spectrally concentrated emission fromsodium street lights would be distinguishable from natural sources using proposed next generation space telescopes. The proposedLUVOIR A may be able to detect city lights twelve times those of Earth onProxima b in 300 hours.[33]
Artist's illustration of an advanced ET civilization with industrial pollution[34]
Atmospheric analysis of planetary atmospheres, as is already done on various Solar System bodies and in a rudimentary fashion on severalhot Jupiter extrasolar planets, may reveal the presence of chemicals produced by technological civilizations.[35][36] For example, atmospheric emissions from human technology use on Earth, includingnitrogen dioxide andchlorofluorocarbons, are detectable from space.[37] 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.[38][39][40][41][excessive citations] 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.[42]
However, there remains a possibility of mis-detection; for example, theatmosphere of Titan has detectable signatures of complex chemicals that are similar to what on Earth are industrial pollutants, though not the byproduct of civilisation.[43] Some SETI scientists have proposed searching for artificial atmospheres created by planetary engineering to produce habitable environments for colonisation by an ETI.[36]
Extraterrestrial artifacts, influence and spacecraft
Interstellar spacecraft may be detectable from hundreds to thousands oflight-years away through various forms of radiation, such as thephotons emitted by anantimatter rocket orcyclotron radiation from the interaction of a magnetic sail with theinterstellar medium. 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.[44] In addition, smallerBracewell probes within the Solar System itself may also be detectable by means of optical or radio searches.[45][46]Self-replicating spacecraft or their communications networks could potentially be detectable within our Solar system or in nearby star-based systems,[47] if they are located there.[48] Such technologies or their footprints could be in Earth's orbit, on the Moon or on the Earth.
A less advanced technology, and one closer to humanity's current technological level, is the Clarke Exobelt proposed by Astrophysicist Hector Socas-Navarro of theInstituto de Astrofisica de Canarias.[49] This hypothetical belt would be formed by all the artificialsatellites occupyinggeostationary/geosynchronous orbits around anexoplanet. 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 thelight curves fromtransiting exoplanets,[50] but subsequent analysis has questioned this result, suggesting that exobelts detectable by current and upcoming missions will be very rare.[51]
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".[52] Microorganism DNA may have been used for self-replicating messages.[53][additional citation(s) needed] See also:DNA digital data storage
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.[26]
Scientific projects searching for technosignatures
In 2005,Fermilab had an ongoing survey for such spectra by analyzing data from IRAS.[57][58] 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.[59] Fermilab discovered 17 potential "ambiguous" candidates of which four have been named "amusing but still questionable".[10] Other searches also resulted in several candidates, which are, however, unconfirmed.[60]
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 thetransit method, as wereCorot orKepler projects at that time.[61] The principle of the detection remains applicable for future exoplanets missions.[62][63][64]
In 2012, a trio of astronomers led by Jason Wright started a two-year search for Dyson Spheres, aided by grants from theTempleton Foundation.[65]
In 2013, Geoff Marcy received funding to use data from theKepler Telescope to search for Dyson Spheres and interstellar communication using lasers,[66] andLucianne Walkowicz received funding to detect artificial signatures in stellar photometry.[67]
Starting in 2016, astronomerJean-Luc Margot ofUCLA has been searching for technosignatures with large radio telescopes.[2]
In 2016, it was proposed that vanishing stars are a plausible technosignature.[68] 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[69] began more general searches for vanishing and appearing stars, and otherastrophysical transients[68] They identified 100 red transients of "most likely natural origin", while analyzing 15% of the image data. In 2020, the VASCO collaboration started up acitizen science project, vetting through images of many thousands of candidate objects.[70] The citizen science project is carried out in close collaboration with schools and amateur associations mainly in African countries.[71] The VASCO project has been referred to as "Perhaps the most general artefact search to date".[72] In 2021, VASCO's principal investigator Beatriz Villarroel received aL'Oreal-Unesco prize in Sweden for the project.[73] In June 2021, the collaboration published the discovery of nine light sources seemingly appearing and vanishing simultaneously from archival plates taken in 1950.[74] Villarroel's team also found three 16th magnitude stars which had vanished on plates exposed within one hour of each other on 19 July 1952.[75]
Methods and ancillary benefits of the search for various technosignatures.[54]
In June 2020, NASA was awarded their firstSETI-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 technosignaturelibrary.[76][77][78] A 2021scientific review produced by the i.a. NASA-sponsoredonline workshopTechnoClimes 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.[79][54]
In 2021, astronomers proposed a sequence of "verification checks for narrowband technosignature signals" after concluding that technosignature candidateBLC1 could be the result of a form of localradiofrequency interference.[80]
Capabilities for detecting technosignatures with recent, ongoing, and future missions and facilities. Cells colored green indicate that at least such a signature could be detectable for at least one stellar system and there being at least one peer-reviewed publication that has evaluated detectability of that signature.
It has been suggested that observatories on the Moon could be more successful.[81][82] In 2022, scientists provided an overview of the capabilities of ongoing, recent, past, planned and proposed missions and observatories for detecting various alien technosignatures.[83][84]
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 toastroethical[85] and relatedmachine ethics ones (e.g., related to machines' applied ethicalvalues), or include information about aliensocieties orhistories 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.
Participants, NASA Technosignatures Workshop (28 January 2019).NASA and the Search for Technosignatures: A Report from the NASA Technosignatures Workshop.arXiv:1812.08681v2.
^Gertz, John (4 December 2020). "Strategies for the Detection of ET Probes Within Our Own Solar System".Journal of the British Interplanetary Society.74 (2): 47.arXiv:2011.12446.Bibcode:2021JBIS...74...47G.
^Gertz, John (21 October 2021). "The Search for Deliberate Interstellar SETI Signals May Be Futile".Journal of the British Interplanetary Society.74 (11): 414.arXiv:2110.11502.Bibcode:2021JBIS...74..414G.
^Gertz, John; Marcy, Geoffrey (27 April 2022). "Engineering an Interstellar Communications Network by Deploying Relay Probes".arXiv:2204.08296 [physics.pop-ph].
^Zubrin, Robert (1995). "Detection of Extraterrestrial Civilizations via the Spectral Signature of Advanced Interstellar Spacecraft". In Shostak, Seth (ed.).Astronomical Society of the Pacific Conference Series. Progress in the Search for Extraterrestrial Life. Astronomical Society of the Pacific. pp. 487–496.Bibcode:1995ASPC...74..487Z.
^Harris, Michael J. (2002). "Limits from CGRO/EGRET Data on the Use of Antimatter as a Power Source by Extraterrestrial Civilizations".Journal of the British Interplanetary Society.55: 383.arXiv:astro-ph/0112490.Bibcode:2002JBIS...55..383H.
^Sheikh, Sofia Z.; Smith, Shane; Price, Danny C.; DeBoer, David; Lacki, Brian C.; Czech, Daniel J.; Croft, Steve; Gajjar, Vishal; Isaacson, Howard; Lebofsky, Matt; MacMahon, David H. E.; Ng, Cherry; Perez, Karen I.; Siemion, Andrew P. V.; Webb, Claire Isabel; Zic, Andrew; Drew, Jamie; Worden, S. Pete (November 2021). "Analysis of the Breakthrough Listen signal of interest blc1 with a technosignature verification framework".Nature Astronomy.5 (11):1153–1162.arXiv:2111.06350.Bibcode:2021NatAs...5.1153S.doi:10.1038/s41550-021-01508-8.ISSN2397-3366.S2CID239906760.
^Haqq-Misra, Jacob; Schwieterman, Edward W.; Socas-Navarro, Hector; Kopparapu, Ravi; Angerhausen, Daniel; Beatty, Thomas G.; Berdyugina, Svetlana; Felton, Ryan; Sharma, Siddhant; De la Torre, Gabriel G.; Apai, Dániel (1 September 2022). "Searching for technosignatures in exoplanetary systems with current and future missions".Acta Astronautica.198:194–207.arXiv:2206.00030.Bibcode:2022AcAau.198..194H.doi:10.1016/j.actaastro.2022.05.040.ISSN0094-5765.S2CID249240495.
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