The actual science behind SETI’s hunt for clever aliens

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In 1993, a team of scientists published an article in the journal Nature that announced the discovery of a planet that was home to life. Using instruments on the Galileo spaceship, they mapped the surface of the planet and saw continents with colors that are "compatible with mineral soils" and agriculture, large ocean areas with "spectacular reflection" and frozen water at the poles. Analysis of the chemistry of the planet revealed an atmosphere with oxygen and methane that are so abundant that they must come from biological sources. "Galileo found such deviations from equilibrium that the presence of life seems to be the most likely cause," the authors wrote.

However, the most telltale sign of life was measured with Galileo's spectrogram: radio transmissions from the surface of the planet. "Of all of Galileo's scientific measurements, these signals provide the only indication of intelligent, technological life," the authors wrote.

The first author of the paper was Carl Sagan, the astronomer, author, and science communicator. The planet that he and his co-authors described was the Earth.

Twenty years later, as far as we can tell, Earth remains the only planet in the universe where there is an intelligent or other life. But this Galileo flyby on Earth was a case study for future work. It has been confirmed that modern instruments can give us clues about the presence of life on other planets – including intelligent life. Since then we have spent decades of resources and enthusiasm to search for life elsewhere in the universe.

However, one component of this search has largely been overlooked: the search for extraterrestrial intelligence (SETI). This is the area of ​​astronomical research that looks for foreign civilizations by looking for technology indicators called "techno signatures". Despite the strong support from Sagan himself (he even made SETI the focus of his 1985 science fiction novel Contact, which was turned into a hit film in 1997 with Jodie Foster and Matthew McConaughey), SETI's funding and support were compared to Find extraterrestrial life in general.

In SETI's 60-year history, a strong group of astronomers has managed to keep the search alive. Today, this cohort is stronger than ever, although largely ignored by the research community, largely unaffected by NASA, and dismissed by some astronomers as a marginalization. After decades of interest and funding the search for organic life, there are preliminary indications that SETI will revive.

At a time when we're building hardware that should be able to find signatures of life (intelligent or otherwise) in the atmosphere of other planets, SETI astronomers just want a place at the table. The commitment is nothing less than the question of our place in the universe.

Enlarge /. The Arecibo radio telescope in Puerto Rico receives interplanetary signals and transmissions. And it was in the film contact!

Getty Images / Stephanie Maze

How to look for life on other worlds

You may have heard of the search for life on other planets by looking for "biosignatures" – molecules or phenomena that would only occur or continue if there was life. These can be microbes that result from direct sampling of material from the planet (known as "in situ sampling") or through the use of spectroscopic biosignatures such as chemical imbalances in the atmosphere and images of water and agriculture, such as those from the Galileo probe in 1990 were detected, were discovered.

The bio-signature search is currently taking place, but there are restrictions. A spaceship must be sent to another planet for in situ sampling. For example, we did this with rovers that were sent to Mars and the Cassini spacecraft and took water flags from Saturn's moon Enceladus. While in-situ sampling is the ideal option for planets in the solar system, with our current technology it will take thousands of years for a vehicle to reach a planet orbiting another star – and these exoplanets are far more numerous.

In order to recognize spectroscopic biosignatures, we need telescopes such as the James Webb Space Telescope (JWST) or the ground-based Extrem Large Telescope, which are currently under construction. In order to directly image an exoplanet and obtain more precise spectra, future missions such as LUVOIR (Large Ultraviolet Optical Infrared Surveyor) or the Habitable Exoplanet Imaging Mission are required. But all of this is a few years in the future.

However, SETI researchers are interested in "technosignatures" – biosignatures that indicate intelligent life. These are signals that can only come from technology, including television and radio transmitters – such as the radio transmission recognized by the Galileo spacecraft – planetary radar systems or high-power lasers.

The first serious call for the search for techno signatures – and the formal beginning of SETI – came in 1959. That year, physicists Giuseppe Cocconi and Philip Morrison from Cornell University in Nature published a groundbreaking paper that outlined the most likely features of communication with extraterrestrials were. It would make most sense for aliens to communicate with electromagnetic waves over interstellar distances, as they are the only media known to move fast enough to potentially reach us over long distances in space. Within the electromagnetic spectrum, Cocconi and Morrison found that the most promising way to search for radio waves is that they are less likely to be absorbed by planetary atmospheres and require less energy to transmit. In particular, they proposed a narrowband signal around the frequency with which hydrogen atoms emit radiation – a frequency that should be known to every civilization with advanced radio technology.

The special thing about these signals is that they have a high degree of coherence, which means that there is a large amount of electromagnetic energy in just one frequency or in a very short period of time – something that nature does not normally do.

"As far as we know, such (radio) signals would be unmistakable indicators of technology," says Andrew Siemion, professor of astronomy at the University of California at Berkeley. "We don't know of any natural source that produces it."

Such a signal was discovered on August 18, 1977 by Ohio State University's Radio Observatory, known as the "Big Ear". Astronomy professor Jerry Ehman analyzed big-ear data in the form of printouts that, to the inexperienced eye, looked as if someone had simply smashed the typewriter number series, with lower digits being preferred. Numbers and letters in the big ear data essentially indicate the intensity of the electromagnetic signal picked up by the telescope, starting with 1 and up to two-digit letters (A was 10, B was 11, etc.). . Most of the page was covered in 1s and 2s, with 6 or 7 sprinkles.

But that day Ehman found an anomaly: 6EQUJ5. This signal had started at an intensity of 6 – already an outlier on the side – and climbed to E, then Q, peaked at U – the highest power signal Big Ear had ever seen – and then decreased. Ehman circled the sequence with a red pen and wrote "Wow!" Besides.

Unfortunately, SETI researchers were able to use the so-called “Wow! Signal “again, despite many attempts with radio telescopes around the world. To date, no one knows the source of the wow! Signal, and it remains one of the strongest alien transmission candidates ever discovered.

NASA began funding SETI studies in 1975 when, according to former NASA chief historian Steven J. Dick, the idea of ​​extraterrestrial life was still unthinkable. After all, nobody knew then whether there were other planets outside our solar system, let alone life.

In 1992, NASA was most committed to SETI and pledged $ 100 million over ten years to fund the High Resolution Microwave Survey (HRMS), an expansive SETI project led by astrophysicist Jill Tarter. Tarter, one of today's most famous SETI researchers, was the inspiration for Sagan's contact protagonist, Eleanor Arroway.

But less than a year after HRMS started, Congress abruptly canceled the project. "The Great Martian Chase could finally end," said Nevada Senator Richard Bryan, one of the loudest critics. “Millions have been spent to date and we still have to bag one little green guy. Not a single Martian has said take me to your leader, and not a single flying saucer has applied for FAA approval. "

The whole ordeal was "incredibly traumatic," says Tarter. "It (the removal of funds) was so vengeful that we actually became the four-letter S-word that could not be said at NASA headquarters for decades."

Since this humiliating public reprimand by Congress, NASA's astrobiology department has largely focused on the search for biosignatures. And it made sure that his current work is differentiated from SETI. In a report from 2015 it even says: "The traditional search for extraterrestrial intelligence … is not part of astrobiology."

Nevertheless or for this reason, the SETI community quickly regrouped and went to the private sector for financing. The Phoenix project arose from these efforts and rose from the ashes of the HRMS. From February 1995 to March 2004, Phoenix scanned around 800 candidate stars nearby for microwave transmission in three separate campaigns with the Parkes Observatory in New South Wales, Australia. the National Radio Astronomy Observatory on Green Bank, West Virginia; and Arecibo Observatory in Puerto Rico. The project found no evidence of E.T., but was considered the most comprehensive and sensitive SETI program ever undertaken.

At the same time, other projects from the Planetary Society and UC Berkeley (including a project called SERENDIP that is still active) conducted SETI experiments and found a handful of abnormal radio signals, but none appeared a second time.