The most unexplained signals received on Earth – and why scientists say they could be aliens

On Earth, we’re constantly detecting signals from deep space.

Many of these radio waves and other forms of electro–magnetic radiation can be attributed to natural phenomena such as pulsars, colliding stars and the sun.

But some, to this day, remain unexplained – and experts say they could be extraterrestrial in origin.

The ‘WOW’ signal

The most renowned is the famous ‘WOW’ signal that was first detected in 1977.

At the time, astronomers discovered a mysterious signal beaming from space that was so powerful it prompted astronomer Jerry Ehman to write ‘Wow!’ on the telescope’s readout.

For decades, scientists debated whether the signal could have been an attempt at communication from a distant alien civilisation, as there were no known explanations for it.

Recently, a team of experts re–examined the signal’s data with modern techniques and found that it was more than four times stronger than previous estimates. Although scientists believe the signal is likely to have natural origins, they say alien sources can’t yet be ruled out.

Dr Hector Socas–Navarro, director of the European Solar Telescope Foundation, told The Daily Mail: ‘While aliens aren’t completely off the table, it seems that the signal may have originated by a natural astrophysical source.

‘Our goal now is to find that source.’

ASKAP J1832–0911

Earlier this year, experts detected a cosmic entity called ASKAP J1832–0911 emitting joint pulses of radio waves and X–rays for two minutes every 44 minutes some 14,700 light–years from Earth.

This was the first time an object like this, called a long–period transient, had been detected emitting X–rays.

Currently, there is no clear explanation for what causes these signals, or why they ‘switch on’ and ‘switch off’ at such long, regular and unusual intervals.

Experts admit even their best theories do not account for what they’re seeing, as it challenges the rules of physics.

And they said it could mean ASKAP J1832–0911 is an entirely new class of object that humans have never detected before.

FRB 20220610A

In 2024, scientists announced they had identified the origin of a high–energy burst of radio waves that travelled eight billion years through space before reaching Earth.

The signal, also known as a fast radio burst (FRB), is one of hundreds of fleeting blasts of energy detected over the years that some astronomers have speculated could be alien life trying to contact our planet.

While scientists do not know the mechanism behind this extraordinary phenomenon, they have found that the FRB came from a cluster of galaxies that existed when the universe was only five billion years old.

Using NASA’s Hubble Telescope, the team peered into deep space and snapped a clear image of the tightly packed galaxies.

These oddly bright flashes of light, registering in the radio band of the electromagnetic spectrum, appear temporarily and randomly from space.

Possibly originating from black holes, neutron stars or even aliens, they range from a fraction of a millisecond to a few seconds before vanishing without a trace.

The tightly packed galaxies spotted in the latest research would be easier for a growing extraterrestrial civilization to planet hop, astronomer Brian Lacki argued in Cambridge’s International Journal of Astrobiology.

Planet K2–18b

While not a direct signal, one of the strongest pieces of evidence for aliens emerged just a few months ago when scientists told the world about a distant ocean–covered planet that is likely teeming with life.

Astronomers led by the University of Cambridge announced they had detected the most promising signs yet of life outside our solar system.

Using data from the James Webb Space Telescope (JWST), the team identified huge quantities of chemicals only made by living organisms on Earth.

They have picked up the chemical fingerprints of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) – molecules that are primarily produced by microbial life such as marine phytoplankton.

They have been detected in the atmosphere of exoplanet K2–18b, which is located around 124 light–years from Earth in the constellation of Leo.

It is the ‘strongest hint yet’ of biological activity outside our solar system, with experts hailing the ‘huge, transformational moment’.

The planet is orbiting a red dwarf star in what is known as the ‘habitable zone’ – considered the most promising location to find life–supporting planets.

K2–18b is 2.6 times larger and 8.6 times as massive than Earth, and experts believe it is likely covered in an ocean – making it what they call a ‘Hycean world’.

Professor Nikku Madhusudhan, from Cambridge’s Institute of Astronomy, led the research.

‘Given everything we know about this planet, a Hycean world with an ocean that is teeming with life is the scenario that best fits the data we have,’ he said.

‘Decades from now, we may look back at this point in time and recognise it was when the living universe came within reach.

‘This could be the tipping point, where suddenly the fundamental question of whether we’re alone in the universe is one we’re capable of answering.’

WHAT IS THE FERMI PARADOX?

The Fermi Paradox questions why, given the estimated 200-400 billion stars and at least 100 billion planets in our galaxy, there have been no signs of alien life. 

The contradiction is named after its creator, Italian physicist Enrico Fermi.

He first posed the question back in 1950.

Fermi believed it was too extraordinary that a single extra-terrestrial signal or engineering project has yet to be detected in the universe — despite its immense vastness. 

Fermi concluded there must a barrier that limits the rise of intelligent, self-aware, technologically advanced space-colonising civilisations.

This barrier is sometimes referred to as the ‘Great Filter’.

If the main obstacle preventing the colonisation of other planets is not in our past, then the barrier that will stop humanity’s prospects of reaching other worlds must lie in our future, scientists have theorised.  

Professor Brian Cox believes the advances in science and engineering required by a civilisation to start conquering the stars will ultimately lead to its destruction.

He said: ‘One solution to the Fermi Paradox is that it is not possible to run a world that has the power to destroy itself.

‘It may be that the growth of science and engineering inevitably outstrips the development of political expertise, leading to disaster.’

Other possible explanations for the Fermi Paradox include that intelligent alien species are out there, but lack the necessary technology to communicate with Earth.

Some believe that the distances between intelligent civilisations are too great to allow any kind of two-way communication.

If two worlds are separated by several thousand light years, it’s possible that one or both civilisations would become extinct before a dialogue can be established. 

The so-called Zoo hypothesis claims intelligent alien life is out there, but deliberately avoids any contact with life on Earth to allow its natural evolution.