Exoplanet Kepler 62f would need an atmosphere rich in carbon dioxide for water to be in liquid form. Artist's Illustration: NASA Ames/JPL-Caltech/T. Pyle
Upcoming telescopes will give us more power to search for biosignatures on all the exoplanets we’ve found. Much of the biosignature conversation is centred on biogenic chemistry, such as atmospheric gases produced by simple, single-celled creatures. But what if we want to search for technological civilizations that might be out there? Could we find them by searching for their air pollution?
If a distant civilization was giving our planet a cursory glance in its own survey of alien worlds and technosignatures, they couldn’t help but notice our air pollution.
This week we are excited (and honored) to welcome Dr. Jill Tarter to the Weekly Space Hangout. Best known for her work in the field of SETI, tonight Jill will be discussing the search for technosignatures.
Credit: Breakthrough Listen/Univ. of Machester/Daniëlle Futselaar
In 2015, Russian-American billionaire Yuri Milner established Breakthrough Initiatives, a non-profit organization dedicated to advancing space exploration. Central to this effort is Breakthrough Listen, a ten-year international research program dedicated to the Search for Extraterrestrial Intelligence (SETI) and the largest and most sophisticated effort to find intelligent life beyond Earth to date.
In the past five years, the project has made two major data releases (in the June of 2019 and February of 2020) and announced that it found no signs of alien transmissions from the 1,327 nearest star systems. But thanks to an analytical breakthrough recently proposed by researchers from the University of Manchester, it looks as though Breakthrough Listen’s search efforts could be expanded by a factor of more than 200!
The Karl Jansky Very Large Array at night, with the Milky Way visible in the sky. Credit: NRAO/AUI/NSF; J. Hellerman
In July of 2015, Breakthrough Initiatives announced that it was embarking on a ten-year initiative to conduct the largest Search for Extraterrestrial Intelligence (SETI) to date. This initiative was aptly named Breakthrough Listen, which combines state-of-the-art software and data obtained by premier observatories around the world to look for signs of extraterrestrial technological activity (aka. technosignatures).
In recent years, Breakthrough Listen has made two majorreleases of data, and announced a lucrative collaboration with NASA’s Transitting Exoplanet Survey Satellite (TESS) mission. And most recently, Breakthrough Listen announced the release of their catalog of “Exotica” – a diverse list of objects that could be of interest to astronomers that are searching for signs of technosignatures and extraterrestrial intelligence (ETI).
A team of astronomers from UCLA searched for "technosignatures" in the Kepler field data. Credit and Copyright: Danielle Futselaar
To date, astronomers have discovered 4,164 extrasolar planets in 3,085 star systems, with another 5,347 awaiting confirmation. With this many planets available for study, researchers have been able to apply new constraints on how likely habitable planets are. In fact, the latest estimates say there could be 6 billion in the Milky Way alone! Understandably, these discoveries have renewed interest in the Search for Extraterrestrial Intelligence (SETI).
But whereas the search for habitable planets is focused on finding evidence of biological processes (aka. “biosignatures”), SETI has historically been focused on evidence of technological activity – aka. “technosignatures.” With a grant from NASA, researchers from the Harvard-Smithsonian Center for Astrophysics (CfA) and the University of Rochester are gearing up for a new study that will look for different kinds of potential technosignatures.
An artist's illustration of a light-sail powered by a radio beam (red) generated on the surface of a planet. The leakage from such beams as they sweep across the sky would appear as Fast Radio Bursts (FRBs), similar to the new population of sources that was discovered recently at cosmological distances.
Credit: M. Weiss/CfA
When it comes to the challenges posed by interstellar travel, there are no easy answers. The distances are immense, the amount of energy needed to make the journey is tremendous, and the time scales involved are (no pun!) astronomical. But what if there was a way to travel between stars using ships that take advantage of natural phenomena to reach relativistic velocities (a fraction of the speed of light).
Already, scientists have identified situations where objects in our Universe are able to do this – including hypervelocity stars and meteors accelerated by supernovae explosions. Delving into this further, Harvard professors Manasvi Lingam and Abraham Loeb recently explored how interstellar spacecraft could harness the waves produced by a supernova explosion in the same way that sailing ships harness the wind.
Artist's impression of a Dyson Sphere. The construction of such a massive engineering structure would create a technosignature that could be detected by humanity. Credit: SentientDevelopments.com/Eburacum45
In 1961, famed astronomer Frank Drake created a formula for estimating the number of extra-terrestrial intelligences (ETIs) that could exist within our galaxy. Known as the “Drake Equation“, this formula demonstrated that even by the most conservative estimates, our galaxy was likely to host at least a few advanced civilizations at any given time. About a decade later, NASA officially kicked of its search for extra-terrestrial intelligence (SETI) program.
These efforts have experienced a major infusion of interest in recent decades thanks to the discovery of thousands of extrasolar planets. To address the possibility that life may exist out there, scientists are also relying on sophisticated tools to search for telltale indicators of biological processes (aka. biosignatures) and technological activity (technosignatures), which could indicate not only life but advanced intelligence.
Artist's impression of a Dyson Sphere. The construction of such a massive engineering structure would create a technosignature that could be detected by humanity. Credit: SentientDevelopments.com/Eburacum45
A team of astronomers from UCLA searched for "technosignatures" in the Kepler field data. Credit and Copyright: Danielle Futselaar
When it comes to looking for life on extra-solar planets, scientists rely on what is known as the “low-hanging fruit” approach. In lieu of being able to observe these planets directly or up close, they are forced to look for “biosignatures” – substances that indicate that life could exist there. Given that Earth is the only planet (that we know of) that can support life, these include carbon, oxygen, nitrogen and water.
However, while the presence of these elements are a good way of gauging “habitability”, they are not necessarily indications that extra-terrestrial civilizations exist. Hence why scientists engaged in the Search for Extra-Terrestrial Intelligence (SETI) also keep their eyes peeled for “technosignatures”. Targeting the Kepler field, a team of scientists recently conducted a study that examined 14 planetary systems for indications of intelligent life.
The Green Bank Telescope is the world’s largest, fully-steerable telescope, which is currently being used in a new SETI (Search for Extraterrestrial Intelligence) attempt to look for possible alien radio signals from Tabby’s Star. Credit: NRAO/AUI/NSF
Together, the team selected 14 systems from the Kepler catalog and examined them for technosignatures. While radio waves are a common occurrence in the cosmos, not all sources can be easily attributed to natural causes. Where and when this is the case, scientists conduct additional studies to try and rule out the possibility that they are a technosignature. As Professor Margot told Universe Today via email:
“In our article, we define a “technosignature” as any measurable property or effect that provides scientific evidence of past or present technology, by analogy with “biosignatures,” which provide evidence of past or present life.”
For the sake of their study, the team conducted an L-band radio survey of these 14 planetary systems. Specifically, they looked for signs of radio waves in the 1.15 to 1.73 gigahertz (GHz) range. At those frequencies, their study is sensitive to Arecibo-class transmitters located within 450 light-years of Earth. So if any of these systems have civilizations capable of building radio observatories comparable to Arecibo, the team hoped to find out!
Spring 2016 UCLA SETI class with Larry Lesyna. Credit: UCLA
“We searched for signals that are narrow (< 10 Hz) in the frequency domain,” said Margot. “Such signals are technosignatures because natural sources do not emit such narrowband signals… We identified approximately 850,000 candidate signals, of which 19 were of particular interest. Ultimately, none of these signals were attributable to an extraterrestrial source.”
What they found was that of the 850,000 candidate signals, about 99% of them were automatically ruled out because they were quickly determined to be the result of human-generated radio-frequency interference (RFI). Of the remaining candidates, another 99% were also flagged as anthropogenic because their frequencies overlapped with other known sources of RFI – such as GPS systems, satellites, etc.
The 19 candidate signals that remained were heavily scrutinized, but none could be attributed to an extraterrestrial source. This is key when attempting to distinguish potential signs of intelligence from radio signals that come from the only intelligence we know of (i.e. us!) Hence why astronomers have historically been intrigued by strong narrowband signals (like the WOW! Signal, detected in 1977) and the Lorimer Burst detected in 2007.
In these cases, the sources appeared to be coming from the Messier 55 globular cluster and the Large Magellanic Cloud, respectively. The latter was especially fascinating since it was the first time that astronomers had observered what are now known as Fast Radio Bursts (FRBs). Such bursts, especially when they are repeating in nature, are considered to be one of the best candidates in the search for intelligent, technologically-advanced life.
The UCLA SETI Group banner, featuring a photo of the central region of the Milky Way Galaxy. Credit: Yuri Beletsky/Carnegie Las Campanas Observatory
Unfortunately, these sources are still being investigated and scientists cannot attribute them to unnatural causes just yet. And as Professor Margot indicated, this study (which covered only 14 of the many thousand exoplanets discovered by Kepler) is just the tip of the iceberg:
“Our study encompassed only a small fraction of the search volume. For instance, we covered less than five-millionths of the entire sky. We are eager to scale the effort to sample a larger fraction of the search volume. We are currently seeking funds to expand our search.”
Between Kepler‘s first and second mission (K2), a total of 5,118 candidates and 2,538 confirmed exoplanets have been discovered within our galaxy alone. As of February 1st, 2018, a grand total of 3,728 exoplanets have been confirmed in 2,794 systems, with 622 systems having more than one planet. On top of that, a team of researchers from the University of Oklahoma recently made the first detection of extra-galactic planets as well!
It would therefore be no exaggeration to say that the hunt for ETI is still in its infancy, and our efforts are definitely beginning to pick up speed. There is literally a Universe of possibilities out there and to think that there are no other civilizations that are also looking for us seems downright unfathomable. To quote the late and great Carl Sagan: “The Universe is a pretty big place. If it’s just us, seems like an awful waste of space.”
And be sure to check out this video of the 2017 UCLA SETI Group, courtesy of the UCLA EPSS department:
