Editing Extraterrestrial life (section)

===Search for extraterrestrial intelligences===
{{main|Search for extraterrestrial intelligence}}
[[File:Green Bank 100m diameter Radio Telescope.jpg|thumb|The [[Green Bank Telescope]] is one of the [[radio telescope]]s used by the [[Breakthrough Listen]] project to search for alien communications.]]
Although most searches are focused on the biology of extraterrestrial life, an extraterrestrial intelligence capable enough to develop a [[civilization]] may be detectable by other means as well. Technology may generate [[technosignature]]s, effects on the native planet that may not be caused by natural causes. There are three main types of techno-signatures considered: [[interstellar communication]]s, effects on the atmosphere, and planetary-sized structures such as [[Dyson sphere]]s.<ref name="techno">{{cite web |url= https://exoplanets.nasa.gov/news/1765/searching-for-signs-of-intelligent-life-technosignatures/|title= Searching for Signs of Intelligent Life: Technosignatures|author= Pat Brennan|date= |publisher= NASA|accessdate=July 4, 2023}}</ref>

Organizations such as the [[SETI Institute]] search the cosmos for potential forms of communication. They started with [[radio waves]], and now search for [[laser pulse]]s as well. The challenge for this search is that there are natural sources of such signals as well, such as gamma-ray bursts and supernovae, and the difference between a natural signal and an artificial one would be in its specific patterns. Astronomers intend to use [[artificial intelligence]] for this, as it can manage large amounts of data and is devoid of biases and preconceptions.<ref name="techno"/> Besides, even if there is an advanced extraterrestrial civilization, there is no guarantee that it is transmitting radio communications in the direction of Earth. The length of time required for a signal to travel across space means that a potential answer may arrive decades or centuries after the initial message.<ref>{{cite web |url=http://www.coseti.org/ |publisher=The Columbus [[Optical SETI]] Observatory |title=The Search for Extraterrestrial Intelligence (SETI) in the Optical Spectrum}}</ref>

The atmosphere of Earth is rich in [[nitrogen dioxide]] as a result of [[air pollution]], which can be detectable. The natural abundance of carbon, which is also relatively reactive, makes it likely to be a basic component of the development of a potential extraterrestrial technological civilization, as it is on Earth. [[Fossil fuel]]s may likely be generated and used on such worlds as well. The abundance of [[chlorofluorocarbon]]s in the atmosphere can also be a clear technosignature, considering their role in [[ozone depletion]]. [[Light pollution]] may be another technosignature, as multiple lights on the night side of a rocky planet can be a sign of advanced technological development. However, modern telescopes are not strong enough to study exoplanets with the required level of detail to perceive it.<ref name="techno"/>

The [[Kardashev scale]] proposes that a civilization may eventually start consuming energy directly from its local star. This would require giant structures built next to it, called Dyson spheres. Those speculative structures would cause an excess infrared radiation, that telescopes may notice. The infrared radiation is typical of young stars, surrounded by dusty [[protoplanetary disk]]s that will eventually form planets. An older star such as the Sun would have no natural reason to have excess infrared radiation.<ref name="techno"/> The presence of heavy elements in a star's light-spectrum is another potential [[biosignature]]; such elements would (in theory) be found if the star were being used as an incinerator/repository for nuclear waste products.<ref>{{cite journal |last1=Whitmire |first1=Daniel P. |last2=Wright |first2=David P. |title=Nuclear waste spectrum as evidence of technological extraterrestrial civilizations |journal=Icarus |date=April 1980 |volume=42 |issue=1 |pages=149–156 |doi=10.1016/0019-1035(80)90253-5 |bibcode=1980Icar...42..149W}}</ref>