"We might soon be able to detect signals from an alien civilization communicating with its spacecraft."
Spaceships in the Night
A nearby star system has just served as the proving ground for a new technique to search for signs of extraterrestrial life.
As detailed in a study set to be published in The Astronomical Journal, astronomers have developed a method that allows alien hunters to listen for much smaller bandwidth radio signals, resembling what we use to communicate with our own spacecraft.
To test it, they set their sights on the TRAPPIST-1 star system, which is only 41 light years away. At its center is a cool red dwarf, surrounded by seven rocky, Earth-sized exoplanets, three of which orbit within their star's habitable zone, which means they could harbor water and support life.
While they didn't pick up on any alien technosignatures, they successfully demonstrated that their technique worked. If applied elsewhere in the cosmos, it could be used to pick up on communications that weren't intended to reach deep space.
"Most searches assume a powerful signal, like a beacon intended to reach distant planets, because our receivers have a sensitivity limit to a minimum transmitter power beyond anything we unintentionally send out," said study lead author Nick Tusay, an astronomer at Penn State University, in a statement about the work. "But, with better equipment, like the upcoming Square Kilometer Array, we might soon be able to detect signals from an alien civilization communicating with its spacecraft."
Occult Techniques
If an alien civilization was like ours, they might be sending plenty of radio signals between their system's planets, perhaps to off-world probes and rovers. These communications would be made over narrowband radio signals, which require less power to send out. Because they're smaller, however, they're also much harder to detect at great distances.
To compensate for this, the team waited for what's known as planet-planet occultations to occur. This is when one planet passes in front of another from our perspective on Earth (think a solar eclipse), providing a rare chance to catch radio "spillover" of a signal being sent from the further world to the nearer one.
In hopes of snagging one of these communications, the researcher used the Allan Telescope Array, a large series of radio telescopes, to scan TRAPPIST-1 for an impressive 28 hours — the longest single-target search in the star system.
Spring a TRAPPIST
During this window, around seven possible planet-planet occultations were predicted to have occurred, producing around 2,200 candidate radio signals that coincided with the astronomical events.
None of these turned out to be the work of little green men. The fact that they were able to identify promising signals at all, however, is proof enough that their technique could pick up on day-to-day radio signals in other stellar neighborhoods.
"The TRAPPIST-1 system is relatively close to Earth, and we have detailed information about the orbit of its planets, making it an excellent natural laboratory to test these techniques," Tusay said. "The methods and algorithms that we developed for this project can eventually be applied to other star systems and increase our chances of finding regular communications among planets beyond our solar system, if they exist."
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