The TRAPPIST-1 system is a compact system of at least seven exoplanets with sizes similar to Earth. Penn State and SETI Institute astronomers spent 28 hours scanning this system for alien radio technosignatures with the Allen Telescope Array. The project marks the longest single-target search for radio signals from TRAPPIST-1. Although the astronomers didn’t find any evidence of extraterrestrial technology, their work introduced a new way to search for radio technosignatures in the future.
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This artist’s impression shows the view from the surface of one of the exoplanets in the TRAPPIST-1 planetary system. Image credit: ESO / M. Kornmesser / Spaceengine.org.
TRAPPIST-1 is an ultracool dwarf star in the constellation Aquarius, 38.8 light-years away.
The star is barely larger than Jupiter and has just 8% of our Sun’s mass. It is rapidly spinning and generates energetic flares of UV radiation.
TRAPPIST-1 is host to seven transiting planets, named TRAPPIST-1b, c, d, e, f, g and h.
All these planets are similar in size to Earth and Venus, or slightly smaller, and have very short orbital periods: 1.51, 2.42, 4.04, 6.06, 9.21, 12.35 and 20 days, respectively.
They are likely all tidally locked, meaning the same face of the planet is always pointed at the star, as the same side of the Moon is always pointed at Earth. This creates a perpetual night side and perpetual day side on each TRAPPIST-1 planet.
Three of the planets, TRAPPIST-1e, f and g, lay in the star’s habitable zone, meaning they may harbor suitable conditions for life.
“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,” said Nick Tusay, a graduate student at Penn State University.
“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.”
Tusay and his colleagues focused on a phenomenon called planet-planet occultations.
These occultations happen when one planet moves in front of another. If intelligent life exists in that star system, radio signals sent between planets could leak and be detected from Earth.
Using the upgraded Allen Telescope Array, the astronomers scanned a wide range of frequencies, looking for narrowband signals, which are considered possible signs of alien technology.
They filtered millions of potential signals, narrowing down to about 11,000 candidates for detailed analysis.
They detected 2,264 of these signals during predicted planet-planet occultation windows. However, none of the signals were of non-human origin.
The Allen Telescope Array’s new capabilities, which include advanced software to filter signals, helped the researchers separate possible alien signals from Earth-based ones.
They believe that refining these methods and focusing on events like planet-planet occultations could help increase the chances of detecting alien signals in the future.
The scientists did not find any alien signals this time, but they will continue improving their search techniques and exploring other star systems.
Future searches with bigger and more powerful telescopes could help scientists detect even fainter signals and expand our understanding of the Universe.
“This research shows we are getting closer to detecting radio signals similar to the ones we send into space,” Tusay said.
“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.”
“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.”
The team’s results will appear in the Astronomical Journal.
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Nick Tusay et al. 2024. A Radio Technosignature Search of TRAPPIST-1 with the Allen Telescope Array. AJ, in press; arXiv: 2409.08313
