Are aliens sending radio signals to each other?

In a distant corner of our galaxy, 41 light years from Earth, the TRAPPIST-1 star system contains seven planets orbiting a red dwarf star.

Some of these planets are in the habitable zone, where conditions might be suitable for life as we know it, and where experts hope to possibly intercept alien signals. It’s an irresistible invitation to explore the potential for life beyond Earth.

Detecting radio signals from alien planets

A dedicated group of scientists from the SETI Institute and Penn State University embarked on a quest to detect alien signals from TRAPPIST-1. Their tool of choice? The Allen Telescope Array (ATA), an array of radio antennas aimed at the cosmos like an eager ear, straining for whispers of alien technology.

For 28 continuous hours, the team scoured the system, seeking radio signals that could be indicative of extraterrestrial technology.

This endeavor represents the most extended single-target search for radio signals from TRAPPIST-1. Despite not stumbling upon outright evidence of alien presence, the expedition has unearthed a wealth of valuable data and has pointed the way to a new path to detect signals in the future.

Communication from extraterrestrial civilizations

“This research shows we are getting closer to detecting radio signals similar to the ones we send into space,” said Nick Tusay, a research fellow at Penn State University.

The existing receiver technology, however, does have its limitations. “Most searches assume some intent, like beacons, because our receivers have a sensitivity limit to a minimum transmitter power beyond anything we unintentionally send out,” noted Tusay.

However, with the advent of more sophisticated equipment, like the upcoming Square Kilometer Array (SKA), Tusay believes we could soon detect signals from extraterrestrial civilizations communicating with their spacecraft.

Narrowband signals and alien technology

The focus of the project was planet-planet occultations (PPOs), which occur when one planet moves in front of another from our vantage point here on Earth. If intelligent life exists on those planets, any radio signals exchanged between them might leak out.

“PPOs may provide a unique opportunity to observe radio ‘spillover’ from extraterrestrial intelligences’ (ETIs) radio transmissions or radar being transmitted from the further exoplanet towards the nearer one for the purposes of communication or scientific exploration,” wrote the researchers.

Armed with the upgraded Allen Telescope Array, the team scanned a wide range of frequencies. They searched for narrowband signals – possible fingerprints of alien technology.

Millions of potential signals were sieved, and around 11,000 candidates underwent further analysis. Of these, 2,264 signals were picked up during predicted PPO windows.

However, none of these signals turned out to originate from a non-human source.

Filtering out human signals to find aliens

The new capabilities of the Allen Telescope Array, with advanced software designed to filter signals, assisted the team in separating potential alien signals from ones originating on Earth.

The researchers believe that refining these techniques and focusing on events like PPOs might increase the chances of detecting elusive alien signals in the future.

“This project included work by undergraduate students in the 2023 SETI Institute Research Experience for Undergraduates (REU) program,” noted Dr. Sofia Sheikh.

“The students looked for signals from human-made orbiters around Mars to check if the system could detect signals correctly. It was an exciting way to involve students in cutting-edge SETI research.”

Future searches with more powerful telescopes

The TRAPPIST-1 system is a tantalizing target. Its proximity to Earth – along with the detailed information available regarding the orbits of its planets – provide a natural laboratory to test these techniques.

The SETI team will continue to refine their search techniques while also exploring other star systems.

The realistic hope is that future searches with larger and more powerful telescopes might allow scientists to detect even fainter signals, thereby broadening our understanding of the universe.

Who knows what the future holds? Will our descendants be talking to our extraterrestrial neighbors as casually as we chat with our friends across continents today?

The study will be published in The Astronomical Journal. The pre-print is available on arXiv.

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