Technosignature

Technosignature is a term used by astrobiologists to describe any sign of technology created by extraterrestrial life. The term was coined in 2007 by astronomer Jill Tarter and is a contraction of the words “technological” and “signatures.” The search for technosignatures is an extension of the search for biosignatures, or signs of past or present life on another planet.

The idea that extraterrestrial life might exist became popular in the 1950s and 1960s, and NASA funded a project to search for signals of extraterrestrial origin. However, the project only lasted a year due to criticism from government officials, who called it a waste of money.

Research is scant on technosignatures. The field receives little funding, and as of 2022, only ten doctoral degrees were awarded to dissertations dedicated to the search for technosignatures. While astrobiologists have not yet confirmed a technosignature, they have detected radio signals from the direction of Proxima Centauri, the closest star to Earth. In addition to this, they have suggested that the presence of pollution and nightside brightness, which could be indicative of city lights, may possibly be technosignatures.

Background

The Search for Intelligent Life

The Search for Extraterrestrial Intelligence (SETI) refers to the scientific search for life outside Earth. This includes technosignatures, or signs of technology created by extraterrestrial life. In the late 1950s and early 1960s, the world had great interest in UFOs (unidentified flying objects) and the possibility of life on other planets. During this time, Frank Drake, a radio astronomer at the National Radio Astronomy Observatory (NRAO) in West Virginia, first introduced the idea that intelligent life on other planets may be using radio waves to contact those on Earth. In 1960, Drake conducted Project Ozma, the first dedicated attempt at seeking out messages from extraterrestrial life. Drake scanned the sky using an 85-foot (26-meter) radio dish. He used a loudspeaker to listen for messages hidden within static. This project drew both media and academic attention. A year later, the first SETI meeting brought together dozens of leading researchers who discussed formalizing Drake’s efforts.

Astronomer Jill Tarter was one of the first researchers dedicated to exploring technosignatures. She launched a project in 1992 called the NASA High Resolution Microwave Survey, which searched for signals of extraterrestrial intelligence. The project came to a halt a year later when Nevada Senator Richard Bryan referred to it as “the great Martian chase” and a waste of government money. In response, Congress effectively shut down the project and banned NASA from funding any further research related to SETI. Tarter then co-founded the privately funded SETI Institute to continue her research.

In 1993, Michel Mayor and Didier Queloz, Swiss astronomers at the Geneva Observatory, constructed a new instrument that could discover new worlds beyond our solar system, which are also known as “exoplanets.” In 1995, they reported their findings and success in discovering the first known planet orbiting a star similar to the sun. As of November 2024, more than 5,600 exoplanets had been discovered. This discovery led researchers to believe more in the possibility of life on other planets. This, in turn, led to the search for “biosignatures,” or chemical evidence that suggested life on other planets. For example, methane and oxygen together on a planet is a biosignature. On Earth, oxygen is produced by photosynthesis while methane gas is produced when microbes eat organic matter. Methane quickly disappears from an oxygen-rich atmosphere such as Earth unless it is steadily replenished by some means. Therefore, the presence of these two gases suggests the possibility of life on a planet.

Biosignatures include any evidence of the existence of microbial or primitive life on other planets, but Tarter believed the same rules could be applied to SETI as well. She believed that advanced aliens could visibly alter their planet by creating a manufactured, industrial civilization. She presented her concept to the International Astronomical Union (IAU) in 2006, arguing that SETI needed a broader definition. Tarter officially coined the term “technosignature” in 2007 during her time as director of the Center for SETI Research.

Types of Technosignatures

The term technosignature encompasses more than one sign of extraterrestrial life. Radio transmissions are the most popular technosignature. Any abnormal observations in radio transmissions could indicate something unnatural. Another possible example of a technosignature is an ultrafast blinking star, which would not be a natural phenomenon and could indicate an advanced civilization. There are several major classes of technosignatures: chemical signatures such as atmospheric pollution; megastructures that reflect, absorb, or block light from a planet’s host star; self-luminous signals such as artificial illumination, radio, or laser communication; and waste heat.

Technosignatures Today

Because the search for technosignatures lacked funding for research for decades, the field is not as developed as other aspects of astrobiology, such as the search for biosignatures. The literature is scant and dominated by only a few privately funded search strategies. The field also lacks curriculum at the university graduate level.

In December 2020, it was announced that scientists studying data collected by the Parkes radio telescope in Australia found a radio signal that came from the direction of Proxima Centauri, which at 4.2 light-years away, is the closest star to Earth. Proxima Centauri has two exoplanets called Proxima Centauri b and Proxima Centauri c. According to scientists, Proxima Centauri b could be habitable to life, so the signal may have come from extraterrestrial beings. The signal was discovered using private funds provided to search for extraterrestrial life. The radio signal appeared several times in April and May 2020.

Researchers believe that the radio signals may have come from extraterrestrial life for several reasons. First, the signal frequency of 982 megahertz is not typically used by spacecraft. In addition, the signal reappeared after the telescope focused on a different part of the sky during a calibration and then returned to Proxima Centauri. Lastly, scientists could not identify any known astrological occurrences that would have generated a radio signal like they observed at that frequency. Still, other evidence could suggest that the signal was not due to alien life. For example, the signal shifted slightly in frequency, which could point to it being produced by a transmitter on a planet orbiting Proxima Centauri. However, the shift was in the wrong direction, according to researchers. It is also difficult to verify the observation since only researchers from Parkes identified the signal. Therefore, it is nearly impossible to verify that the signal came from Proxima Centauri. Also, the signal may have been caused by something behind Proxima Centauri. Despite not being able to prove their theory, however, researchers believed the signal to be one of the most compelling candidates for a technosignature to date.

In 2021, NASA announced that pollution could be the key to finding extraterrestrial life. A 2021 study examined the presence of nitrogen dioxide in the atmosphere. On Earth, nitrogen dioxide is produced by burning fossil fuels, biology, lightning strikes, and volcanos. However, the majority of nitrogen dioxide is caused by human activity. Therefore, observing nitrogen dioxide on a habitable planet could indicate the presence of an advanced civilization. Researchers believe that if they observe more nitrogen dioxide than could be generated from non-industrial sources, some nitrogen dioxide may have stemmed from industrial activities. While they recognize that a false positive is possible, they hope to learn in the future how to discern positives from false positives.

According to a study conducted in 2022, scientists searching for the possibility of extraterrestrial life should be on the lookout for city lights on exoplanets. More urbanized planets would have higher nightside brightness from city lights. Researchers who conducted the study also urged the astronomical community to think more about the possibility of detecting technosignatures using a community-wide effort. They felt that searching for technosignatures is a logical extension when searching for extraterrestrial life through biosignatures. They pointed out that the idea of searching for technosignatures has been considered by astronomers for more than half a century, with initial efforts focused on the possibility of detecting extraterrestrial radio transmissions.

Those in the SETI community believe that technosignatures could be more abundant, longer lasting, and easier to detect than biosignatures, yet the search for biosignatures receives more funding. Researchers concluded during a second study in 2022 that the search for biosignatures should include the search for technosignatures because the two complement and supplement each other. Both are indicative of life outside of that on Earth.

According to an article on the website Space.com in 2023, scientists had begun using machine learning, a type of artificial intelligence, to detect technosignatures. The scientists used new computer algorithms to analyze data that had been collected by the Green Bank Telescope in West Virginia to find signals that might be coming from advanced extraterrestrial civilizations. These new algorithms were able to organize the data from the telescope into categories, so they could distinguish between actual signals and interference. They discovered eight signals that resembled potential technosignatures. However, they need to detect the same signals multiple times to confirm that they originated from extraterrestial intelligence.

Bibliography

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Davis, Jason. “Aliens at Proxima Centauri? A New Radio Signal Raises the Question.” The Planetary Society, 22 Dec. 2020, www.planetary.org/articles/aliens-at-proxima-centauri-a-new-radio-signal-raises-the-question. Accessed 22 Aug. 2022.

Kaufman, Marc. “Technosignatures and the Search for Extraterrestrial Intelligence.” Astrobiology at NASA, July 2022, astrobiology.nasa.gov/news/technosignatures-and-the-search-for-extraterrestrial-intelligence/. Accessed 22 Aug. 2022.

Lea, Robert. "Machine Learning Spots Eight Possible Technosignatures." Space.com, 31 Jan. 2023, www.space.com/machine-learning-seti-technosignatures. Accessed 8 Nov. 2024.

Powell, Corey S. “The Search for Alien Tech.” Aeon, 25 Oct. 2021, aeon.co/essays/technosignatures-are-a-sea-change-in-the-search-for-alien-life. Accessed 22 Aug. 2022.

Tarter, J.C. & Gulkis, S. “The NASA High Resolution Microwave Survey.” Bulletin of the American Astrological Society, May 1993, ui.adsabs.harvard.edu/abs/1993AAS...182.7101T/abstract. Accessed 22 Aug. 2022.