If aliens are watching Earth, they might be able to detect us from the radio signals we beam to Mars to control our rovers there. Astronomers have now listened in on the nearby TRAPPIST-1 system to check whether aliens are chattering between their own neighboring planets.
Earth has been blasting out incidental radio signals for over a century now, but contrary to what sci-fi says, these are fairly weak and diffuse in space, so they’d be hard to detect from other planets. But what about those that are specifically designed to reach other planets?
Humans have sent spacecraft all over our neighborhood. We have robots driving around on Mars, orbiters monitoring several planets and the Sun, and even a few probes that have left our solar system. Controlling these takes stronger, more direct radio communications, and if you were in the direct line of fire in the background, there’s a chance you might be able to detect some “spillover” from these signals with the right equipment.
Scientists at Penn State and the Search for ExtraTerrestrial Intelligence (SETI) have now applied that logic to other star systems, to see if maybe we can find alien civilizations using this method. And where better to test the idea than TRAPPIST-1, located just 40 light-years away?
This system is made up of seven rocky, roughly Earth-sized planets that are fairly close together, some of which are in the star’s habitable zone. If intelligent life evolved on one world there, there’s a decent chance it spread to others, so civilizations could be beaming radio messages to each other, or piloting remote robots like our Mars rovers.
If so, the best time to pick up these signals would be when one planet passes in front of the other, from our perspective here on Earth. The team calls these events “planet-planet occultations,” or PPOs. Radio signals could kind of “leak” around the back of the planet and reach us, like sunlight peeking around the shadow of the Moon during an eclipse.
The team used the Allen Telescope Array (ATA) to scan the TRAPPIST-1 system for 28 hours. To identify signals most promising to be artificial, they specifically focused on narrowband radio signals of a certain strength, originating from TRAPPIST-1, which occurred during PPOs.
After applying these filters to millions of incoming radio detections, they arrived at a list of 11,127 candidate signals. These were subjected to detailed analysis, and 2,264 were found to occur during PPO windows. Sadly, on closer inspection none of them were found to have alien origin.
Still, it’s not a complete wash out though. Longer observations of this and other systems, with more powerful instruments, could eventually pick up ET phoning home.
“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,” said Nick Tusay, first author of the study.
The research has been accepted for publication in the Astronomical Journal.
Source: Penn State University