In our search for alien life, stars might be muddying their signals

LISTEN | The hunt for alien signals is getting a rethink:

Quirks and Quarks16:37Narrowing down potential alien signals from 12 billion to 100, thanks to SETI

The only place we know for certain that life exists is here on Earth. But when we look out at the vastness of space — our neighbouring planets and their moons, and the billions more believed to exist in other solar systems — it’s hard not to wonder whether life exists elsewhere in the universe.

While there’s no single accepted definition of life, scientists agree on some of the key clues. Gases like oxygen, carbon dioxide and methane in a planet’s atmosphere can serve as possible indicators of life.

But there is also a smaller field of research that is looking for signs of alien life without relying on biology at all.

Known as the Search for Extraterrestrial Intelligence (SETI), the effort looks for technosignatures — evidence of technology developed by intelligent beings, such as electromagnetic signals — that stand out from the cosmos’s natural background noise.

Pictured here is the Allen Telescope Array, the first radio telescope built specifically for searching for extraterrestrial intelligence (SETI). Located at the Hat Creek Radio Observatory in northern California, it features 42 antennas. (Simon Steel)

Unlike the rumbles of black holes or the whistles of solar winds, these signals would be structured in ways that suggest an artificial origin, much like the radio and television broadcasts Earth sends into space.

If other intelligent life forms have developed similar technologies, they may also be unintentionally leaking signals that our antennas could one day detect.

But a study published in March in The Astrophysical Journal points to an overlooked complication in that type of search: space weather from stars, where potential signals originate, could be interfering.

Since the earliest days of the hunt for intelligent life, scientists have zeroed in on a particular kind of transmission known as a narrowband signal — a beam of energy so tightly focused at a single frequency that it resembles a needle, says Vishal Gajjar, the study’s lead author.

Gajjar is a staff astronomer at the SETI Institute, a non-profit based in Silicon Valley that’s dedicated to understanding the origins of life.

He says narrowband signals became a prime target because they are unlikely to arise from known natural astrophysical processes, especially when they’re detected in the same place more than once, which raises the possibility they could be generated by distant intelligent life.

A man wearing a blue jacket smiles at the camera. — Vishal Gajjar is a staff astronomer at the SETI Institute and a project scientist for Breakthrough Listen at the University of California, Berkeley. (Submitted by Vishal Gajjar)

A signal lost in the noise

But despite decades of searching, scientists have been met largely with radio silence — prompting them to ask whether a fundamental property of the stars that planets orbit could be muddying the signals.

Every star, including our own sun, says Gajjar, is surrounded by an interplanetary medium: a chaotic mix of plasma and magnetic fields stirred by stellar winds, flares and occasional violent eruptions of even more disruptive coronal mass ejections from the host star.

If a narrowband signal passes through it, especially when it’s stormy, it can become significantly broadened, which makes it wider and flatter than most instruments would catch, he says.

His takeaway? “We need to adjust our search strategy.”

To understand how stars might affect the search, Gajjar and his team turned to a natural laboratory: spacecraft in our solar system.

Radio transmissions between Earth and these probes already travel through the sun’s turbulent plasma and solar wind and offer real-world examples of how narrowband signals are altered.

By analyzing these wider and flatter transmissions, the researchers calibrated models describing how a star’s outflow reshapes a signal’s spectrum.

They used their findings to create a framework to estimate how much a star might interfere with transmissions in different systems.

Observations of our own solar system confirm that narrowband signals often broaden under the sun’s chaotic influence, and Gajjar’s team concluded that similar effects are likely across the galaxy.

“If [the signals from alien life] happen to be originating from a planet around any star, they will be spectrally broadened,” said Gajjar.

A graphic shows a sharp white needle like signal on the left and on the right is a flattened out green radio signal symbol. — A planet’s radio signal may start as a sharp tone, left, but can be broadened by the star’s surrounding plasma winds into a wider, fainter signal, right. ( Vishal Gajjar)

The study, he says, also shows that space weather varies widely between stars, with some environments far more disruptive to narrowband signals than others.

M dwarf stars, which make up roughly three-quarters of the Milky Way, are a prime example.

These small, active stars are incredibly long-lived — none that have ever formed in the universe have yet died — making them abundant and potentially excellent hosts for planets where life could evolve.

But their strong magnetic activity and frequent flares can weaken and broaden signals, making detection from Earth far more difficult.

Rethinking the search for intelligence

Gajjar says the study suggests that looking for “needle-like” signals is unlikely to succeed.

Instead, tools will need to adapt to detect wider, fainter signals, he says, as stellar turbulence can broaden a transmission — from 1 hertz to 10 hertz — reducing its intensity by nearly 94 per cent.

Despite these challenges, Gajjar remains optimistic about the search for life beyond Earth.

Advances in technology now allow instruments to scan wider bandwidths and analyze signals in ways that were impossible just decades ago.