Space is full of periodic and fairly complex signals of entirely natural origin. This makes it much harder to find anything among them that might come from extraterrestrials. Ordinary fireflies, however, could offer a clue about how to approach the problem.
A New Perspective on Extraterrestrial Communication
Inspired by the way terrestrial fireflies communicate, a group of scientists has developed an experimental model for detecting possible signals from extraterrestrial civilizations against the background of natural radio pulses from existing pulsars. The model compares hypothetical signals with those from natural sources while accounting for energy costs, according to phys.org.
Searches for extraterrestrial signals mostly look for what is familiar to us today—primarily radio signals similar to those we have been transmitting for a hundred years. Since 2016, the Breakthrough Listen initiative has also been searching for optical laser signals.
Our shift toward cable television and the internet is making Earth less active at radio wavelengths, and extraterrestrials may also have passed through a similarly brief period of “radio activity.” This suggests that “new conceptual frameworks may be needed to recognize signals from intelligent extraterrestrials in astronomical data,” a group of U.S. scientists writes in Scientific Reports.
Firefly Flashes Inspire a Model of Extraterrestrial Signals
Taking inspiration from the Earth Species Project, in which scientists use machine learning to study animal communication, researchers from universities in the southwestern United States developed a firefly-inspired toy model for signal detection. A toy model is a simplified representation of a complex system designed to highlight its most important features.
During mating season, fireflies produce sequences of flashes, usually at dusk, through the chemical process of bioluminescence in a specialized light-producing organ on their abdomens. These flashes serve as courtship signals, allowing flying males to announce their presence to females on the ground.
Flashing characteristics can vary in duration, synchronization, color, number and frequency of repetitions, emission height, and flight direction. They differ both between species and across geographical regions.
The scientists, led by lead author Cameron Brooks of Arizona State University, drew on a 2022 paper by Chantal Nguyen and colleagues. That study examined how firefly mating signals can co-evolve amid the visual chaos of a swarm while remaining as distinct as possible from those of other firefly species and limiting flashing to conserve energy. Flashing costs fireflies energy and also exposes them to predators.
Radio Pulse Patterns That Minimize Background Signals from Nearby Pulsars
The researchers developed a simplified model that could generate an extraterrestrial signal as distinct as possible from the background of highly ordered natural signals produced by pulsars, while minimizing energy consumption.
Pulsars are highly magnetized, rapidly rotating neutron stars that produce bright, regular radiation in a highly periodic beam sweeping through space. An estimated 100,000 exist in the Milky Way, and we can detect them if their beams sweep across the plane of Earth’s orbit.
These are precisely the kinds of properties we might expect from signals originating from extraterrestrial intelligence. Any intelligent extraterrestrials seeking to announce their location through a pulsed radio beam would therefore probably make an effort to distinguish themselves from nearby pulsars.
The researchers’ model, however, is not designed to search for literal optical flashes resembling firefly light. Instead, it looks for more abstract features of signal patterns: repetition period and pulse duration. Their simplified model sought patterns that minimized overlap with the weighted background signals of nearby pulsars while also minimizing the signalers’ energy consumption, represented by the fraction of time the signal remained on. The model “evolved” to optimize the trade-off between signal properties and energy consumption.
Testing Signals Against a Pulsar Background
To test their model, Brooks and his colleagues developed potential signals by analyzing 3,724 pulsars from the Australia Telescope National Facility database. They divided the pulsars’ pulse profiles into “on” and “off” states, using a user-selected mean flux density threshold. A profile above that threshold was assigned a value of “1,” while one below it received a “0.”
They modeled hypothetical extraterrestrial signals by generating repeating radio pulse patterns optimized to stand out against natural pulsar signals while respecting an energy-consumption constraint.
The main experiment used 158 pulsars within five kiloparsecs, or 16,000 light-years, of Earth to create the natural background, applying energy constraints and working at a frequency of 1,400 megahertz. This frequency is close to the well-known hydrogen emission line at 1,420 MHz, corresponding to a wavelength of 21 centimeters. Because radiation at this frequency—microwaves—penetrates dust clouds, it is favored by astronomers and could also be used by extraterrestrials wishing to announce their existence.
The model measured how closely each simulated signal matched the background pulsars while accounting for different phase shifts in each incoming beam. The peaks and troughs of their wave cycles would not all align. Optimization produced two signal structures: one when energy costs were ignored, and another shared across all tested settings that accounted for energy costs.
This study, which is only a proof of concept, supports a “detection-first” strategy: potentially artificial communication could stand out through its relationship with surrounding signals, even if its content remains incomprehensible to us. The researchers believe this approach would complement, rather than replace, existing SETI methods.
