👽 The silence of extraterrestrials could be due to... space weather

For decades, astronomers have been scanning the sky for radio signals from other planets. So far, no message has been detected. But a new study published in The Astrophysical Journal offers a novel explanation: space weather around exoplanets could scramble these signals, making them undetectable.

This finding provides a clue to answering the famous Fermi paradox: why, despite the vastness of the cosmos and the multitude of potentially habitable planets, have we detected nothing yet?

To test this hypothesis, the researchers focused on a particular type of signal: very narrowband signals. These radio emissions, concentrated on a precise frequency, do not occur naturally and would betray a technological origin. But to detect them, the signal must remain sharp. According to the study, the interplanetary medium, agitated by eruptions from the host star, could spread these signals over a wider frequency range, weakening them and dropping them below the detection threshold.


The scientists analyzed how communications with space probes (Mariner IV, Viking) were affected by our Sun's space weather. Using this data, they modeled the effect of M-type stars, the most numerous in the Milky Way, on potential signals from their planets. Result: these stars produce a wind of charged particles that disperses the signals, making them even harder to detect.

The team proposes a method to estimate the broadening of a signal based on its frequency and the type of star. This tool could help future searches refine their criteria. An astronomer not involved in the study, Michael Garrett, praises this concrete approach grounded in real measurements. However, he notes that the search for narrowband radio signals is only one approach among many to detect an advanced civilization.

Andrew Siemion, director of the Breakthrough Listen program, points out that this is the first time the impact of the space environment around exoplanets on detectability has been studied. According to him, this work offers a concrete mechanism to validate the extraterrestrial origin of a potential signal. The authors recommend that future observatories, such as the SKA-Low telescope, take this dispersion effect into account to optimize their searches.

Thus, the Fermi paradox may find a partial answer: it is perhaps not that no one is transmitting, but that our search methods are not yet adapted to the physical reality of these signals. As the researchers write, the observed silence is not necessarily proof of the absence of transmitters, but a reflection of our detection limitations when faced with signals whose shape does not match what we expect.

Narrowband signals

To distinguish an artificial signal from natural noise, astronomers look for so-called "narrowband" signals. These are radio emissions concentrated in a very restricted frequency range, sometimes only a few hertz. In nature, such signals do not appear spontaneously. Pulsars, gas clouds, or stellar phenomena emit over a wide frequency range. If a receiver picks up a very sharp and stable peak, it is a good candidate for a technological origin.

However, as the study shows, this signal can be "broadened" by its journey through interplanetary plasma. Charged particles deflect radio waves, spreading them over several hertz. As a result, the characteristic peak flattens and resembles a natural signal. Future detection algorithms will therefore need to account for this possible deformation.