How ‘space weather’ may cause alien signals to get lost in space

By Stephen Beech

Aliens may have been trying to contact humans for years, suggests new research.

But stellar “space weather” could mean radio signals from friendly extraterrestrial intelligence get lost in space, say scientists.

Turbulent plasma near distant stars could blur ultra-narrow signals before they leave their home star systems - making them difficult to detect, according to the study.

Researchers from the SETI Institute, based in California, found stellar activity and plasma turbulence near a transmitting planet can broaden an otherwise ultra-narrow signal.

They explained that signal's power is spread across more frequencies, making it more difficult to detect in traditional narrowband searches.

Founded in 1984, the SETI Institute is a non-profit organisation whose mission is to lead humanity’s quest for other life and intelligence in the universe.

For several years, many SETI experiments have focused on identifying spikes in frequency - signals unlikely to be produced by natural astrophysical processes.

But the new research, published in the The Astrophysical Journal, highlights an overlooked complication: even if an alien transmitter produces a perfectly narrow signal, it may not remain narrow by the time it leaves its home system.

In most signal searches, scientists account for distortions that happen as radio waves travel across interstellar space.

The new study focuses on what can happen closer to the source.

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The research team say plasma density fluctuations in stellar winds, as well as occasional eruptive events such as coronal mass ejections, can distort radio waves near their point of origin, effectively “smearing” the signal’s frequency.

The stella interference also reduces the peak strength that search pipelines rely on.

Study lead author Dr. Vishal Gajjar, an astronomer at the SETI Institute, said: “SETI searches are often optimized for extremely narrow signals.

"If a signal gets broadened by its own star’s environment, it can slip below our detection thresholds, even if it’s there, potentially helping explain some of the radio silence we’ve seen in techno-signature searches,”

To quantify the effect, the team built on something that can be measured directly: radio transmissions from spacecraft in our solar system.

Using empirical measurements from solar system probes, they calibrated how turbulent plasma broadens narrowband signals and then extrapolated those measurements to a wide range of stellar environments.

The result is a practical framework for estimating how much broadening could occur for different types of stars and observing frequencies - especially in the “space weather” conditions expected around active stars.

The researchers say their findings point to a strong implication for target selection and search design.

M-dwarf stars, which constitute about 75% of stars in the Milky Way, have the highest likelihood that any narrowband signals will get broadened before leaving the system.

The researchers say that this motivates search strategies that remain sensitive even when signals are not perfectly razor-thin.

Study co-author Grayce Brown, a research assistant at the SETI Institute, added: “By quantifying how stellar activity can reshape narrowband signals, we can design searches that are better matched to what actually arrives at Earth, not just what might be transmitted.”