A cosmic particle detector in Antarctica has picked up a series of inexplicable signals that contradict current models in particle physics.

The anomalies were detected by the Antarctic Impulsive Transient Antenna (ANITA) experiment and consist of radio wave pulses that, instead of reflecting off the ice as expected, seem to emerge from impossible angles in physical interactions that are so far unknown.

The results are published in the journal Physical Review Letters and present a puzzle that points to the existence of new particles or phenomena that do not fit within the Standard Model, which describes elementary particles and their interactions.

An Anomaly Beneath the Ice

ANITA is a set of instruments mounted on high-altitude balloons over Antarctica, designed to track cosmic rays and neutrinos, the particles that travel through the universe almost without interacting with matter.

antarctica radio pulses
The unusual radio pulses were detected by the Antarctic Impulsive Transient Antenna (ANITA) experiment, a range of instruments flown on balloons high above Antarctica that are designed to detect radio waves from cosmic rays hitting the atmosphere. Credit: Stephanie Wissel / Penn State

But instead of capturing signals from space, the detector recorded radio waves that, according to scientists’ calculations, must have traveled through thousands of kilometers of rock before being detected—something that, in theory, should have completely absorbed them.

The radio waves we detected had very steep angles, about 30 degrees below the surface of the ice, explained Stephanie Wissel, associate professor of physics and astrophysics at Penn State and a member of the ANITA team. According to our models, that signal shouldn’t have reached us because the rock would have wiped it out.

What’s most puzzling, according to Wissel, is that these are not neutrinos—the particles the experiment was originally designed to capture. Neutrinos, although abundant in the universe, are also extremely difficult to detect because of their weak interaction with matter. A billion neutrinos pass through your fingernail every second, but almost none leave a trace, the researcher noted.

A New Physics?

To rule out errors, the team compared ANITA’s data with those from other independent detectors, such as the IceCube Observatory and the Pierre Auger Observatory, without finding matches, which ruled out the signals being caused by conventional cosmic rays or high-energy neutrinos.

What we’re seeing doesn’t fit the standard framework of particle physics, Wissel admitted. Among the scientists’ hypotheses is the possibility that these anomalies are related to dark matter, although the lack of similar detections at other observatories complicates that explanation.

In light of the mystery, Penn State and other collaborators are already working on ANITA’s successor, the Payload for Ultrahigh Energy Observations (PUEO), a larger and more sensitive detector that could help understand the origin of these signals. With PUEO, we’ll have better capacity to detect anomalies and maybe actual neutrinos, Wissel said. If we manage to detect them, we could obtain information about cosmic events that happened billions of years ago.

SOURCES

Pennsylvania State University

A.Abdul Halim et al., Search for the Anomalous Events Detected by ANITA Using the Pierre Auger Observatory, Physical Review Letters (2025). DOI: 10.1103/PhysRevLett.134.121003

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