Mysterious Radio Signal Detected from Underneath Antarctic Ice

Scientists once detected a strange signal from underneath the ice in Antarctica and its origin is making them scratch their heads. The Antarctic Impulsive Transient Antenna (ANITA), a balloon-borne instrument designed to detect radio waves from cosmic rays, caught something unexpected in 2006 - a brief pulse of radio waves coming from below the ice, not from above as expected. According to a study published in the Physical Review Letters, a similar signal was detected again in 2014, sparking a scientific mystery that remains unsolved.

"The radio waves that we detected were at really steep angles, like 30 degrees below the surface of the ice," astrophysicist Stephanie Wissel from Pennsylvania State University said in a statement. These signals looked like they could be from a rare particle called a tau neutrino, but the explanation doesn’t quite add up.

Neutrinos are known as "ghost particles" because they can pass through matter without interacting. Neutrinos are subatomic particles which are produced by events like supernova (explosion of a dying star). They are neutral in charge and their mass is so small that it is yet to be accurately measured.

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"You have a billion neutrinos passing through your thumbnail at any moment, but neutrinos don't really interact," Wissel explains. For a neutrino to create these signals, it would need to travel through Earth's core and emerge from the Antarctic ice at a steep angle, which scientists say is an unlikely feat. While the 2014 signal coincided with a supernova, which could produce neutrinos, no such event was linked to the 2006 signal, making the neutrino theory even shakier.

To investigate, researchers turned to the Pierre Auger Observatory in Argentina, which studies high-energy cosmic rays. They analysed data from 2004 to 2018, running simulations to see if similar signals appeared. They found nothing, ruling out neutrinos as the cause.

So, what caused these odd signals? It could be an unknown particle or a strange effect of radio waves interacting with the ice. "My guess is that some interesting radio propagation effect occurs near ice and also near the horizon that I don't fully understand," Wissel says. Scientists are hopeful that a new experiment - Payload for Ultrahigh Energy Observations (PUEO) - a successor of ANITA, will detect more of these signals and provide answers to these questions.

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(Image: Penn State University)