Stephanie Wissel / Penn State
It sounds like something out of science fiction, but scientists have picked up puzzling radio signals originating beneath Antarctica’s ice sheet—signals that don’t quite align with our current understanding of particle physics.
ANITA’s Unexpected Discovery
These strange pulses were initially detected between 2016 and 2018 by NASA’s Antarctic Impulsive Transient Antenna (ANITA), a high-altitude experiment designed to detect cosmic phenomena. Since their discovery, researchers have been working to decipher their origin. A recent study published in Physical Review Letters now offers a fresh angle on the ongoing mystery.
ANITA consists of 24 radio antennas suspended from a balloon flying 40 kilometers (25 miles) above the Antarctic continent. It monitors radio waves entering Earth’s atmosphere, and Antarctica provides an ideal observation point thanks to minimal radio noise.
Typically, ANITA picks up radio waves coming from above. But the unusual events in 2016 and 2018 had signals emerging from deep below the ice. For these radio waves to reach ANITA, they would have had to travel through thousands of kilometers of dense rock—something that should have blocked or absorbed them completely.
Neutrinos No Longer the Leading Theory
“We still don’t have a clear explanation for these anomalies, but it’s unlikely they were caused by neutrinos,” explained Stephanie Wissel, a physics professor and ANITA team member.
Neutrinos—extremely light, neutral subatomic particles—were the main suspects at first. They rarely interact with matter and are known to pass through entire planets undisturbed. These elusive particles are commonly emitted by cosmic phenomena such as supernovae or the sun.
Despite their elusive nature, even a single neutrino can reveal important details about distant cosmic events. ANITA was specifically designed to detect neutrino-induced radio emissions, especially those generated by interactions with Antarctic ice.
When tau neutrinos collide with ice, they can produce tau leptons, which in turn generate bursts of secondary particles and unique radio signals called “air showers.” These signals appear like trails of sparks moving in a single direction, according to Wissel.
Anomalous Signals Defy Expected Patterns
By analyzing such patterns, scientists can often trace the source of a neutrino. However, the anomalous signals didn’t match known neutrino signatures and couldn’t be linked to any clear origin. The team used models and simulations to rule out more conventional explanations.
Researchers also looked for similar signals in data from other observatories—like IceCube and the Pierre Auger Observatory—but none of them had detected anything comparable to what ANITA found.
As a result, neutrinos are no longer considered the most plausible explanation. The radio signals remain classified as “anomalous,” and researchers are now looking ahead to more advanced instruments. One promising option is the upcoming Payload for Ultrahigh Energy Observations (PUEO), which may help unlock the mystery.
Read the original article on: New Atlas
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