- ANITA detected two unexplained radio signals rising through Antarctic ice.
- Neither IceCube nor Pierre Auger found any matching signals.
- The signals are probably not new physics, Wissel says.
Stephanie Wissel was reviewing ANITA data from a balloon floating 40 kilometers above the Antarctic ice, when she encountered a number that didn't make sense. The radio signals her team had recorded were arriving at 30 degrees below the horizon, pointing upward, through the Earth, from thousands of kilometers of solid rock that should have absorbed them entirely.
That data came from NASA's Antarctic Impulsive Transient Antenna, a suite of radio instruments designed to catch neutrinos, the universe's most elusive particles. What ANITA caught instead, during flights between 2006 and 2016, were two signals that no known particle could produce.
A decade later, Wissel and an international research team have published a formal study in Physical Review Letters confirming that the signals remain, in the carefully chosen language of physics, "anomalous."
Key figure
30°
The angle below the ice surface at which ANITA detected the anomalous signals, far steeper than any known particle source can produce
A Detector Built for Silence
ANITA was sent to Antarctica for a characteristically practical reason: the continent generates almost no radio interference. The balloon-borne instrument floats over the ice, pointing its antennas downward to listen for a specific kind of cosmic messenger.
What is a neutrino?
Neutrinos are subatomic particles with no charge and almost no mass. They stream through the universe in vast numbers. A billion pass through your thumbnail every second without touching it. When a high-energy neutrino does interact with matter, it leaves a faint but detectable trace, making these rare collisions windows into cosmic events like supernovae and black hole mergers.
The anomalous signals did not behave like neutrinos. By Wissel's calculations, the particles responsible would have had to travel through thousands of kilometers of rock before reaching the detector. Rock, at those distances, absorbs radio signals completely. There should have been nothing to detect.
Yet ANITA detected something.
Two Observatories Find No Trace of Anomalous Signals
To test whether the signals might have a mundane explanation, Wissel and her colleagues cross-referenced the ANITA data with two of the world's most sensitive particle detectors: IceCube, buried deep in the Antarctic ice sheet, and the Pierre Auger Observatory in Argentina, which monitors an area roughly the size of Luxembourg.
Neither registered anything at the corresponding times and directions.
That null result, intriguingly, rules out the most dramatic theories. The lack of corroborating data from Auger and IceCube means the signals almost certainly do not represent new fundamental particles, and probably do not indicate new physics in the strong sense. "It does not indicate that there is new physics," Wissel said, "but rather more information to add to the story."
Her best current guess is more prosaic: a radio propagation effect near the ice surface and the horizon, one that bends signals in ways existing models don't anticipate. The problem is that her team has searched for that explanation too, and hasn't found it.
PUEO Launches Into the Unknown
The next chapter belongs to PUEO, the Payload for Ultrahigh Energy Observations, which launched from McMurdo Station in December 2025. Led by Abigail Vieregg of the University of Chicago, the 12-institution collaboration has built a successor to ANITA with ten times the sensitivity.
More On Cosmic Tays
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Space telescope identifies natural particle accelerator 100 times more powerful than the Large Hadron Collider.
→PUEO uses an interferometric phased array (dozens of antennas whose signals are combined in real time) to pick out faint events from the continuous radio noise washing over Antarctica from satellites, cosmic rays, and the occasional errant static charge.
Wissel expects PUEO to detect more anomalous signals. Whether those signals will finally reveal their origin, or only deepen the puzzle, remains an open question she finds genuinely appealing. "We also might detect neutrinos," she noted, "which would in some ways be a lot more exciting."
The original ANITA flights were led by Peter Gorham at the University of Hawaii. Fifteen years on, the signals he first flagged as strange still have no explanation, alongside other unexplained optical signals that keep drawing scientists back.
Sources
- Primary Research: Search for the Anomalous Events Detected by ANITA Using the Pierre Auger Observatory (Physical Review Letters, 2025)
- Additional Context:
- Strange radio pulses detected coming from ice in Antarctica (Penn State University)
- To find energetic particles from space, a new detector will soar over Antarctic ice (University of Chicago News)
Fact Check: Claim-by-Claim Verification Verified
The article accurately reflects current research on the ANITA anomalies, their still-unexplained nature, the null results from Auger and IceCube, and the goals and status of PUEO.
Commentary
- The statement that the lack of corroborating data “almost certainly” rules out new fundamental particles is somewhat stronger than the cautious language in the Physical Review Letters paper, which frames the result as being in strong tension with an upward-going flux interpretation; however, the article elsewhere correctly quotes Wissel as not claiming evidence for new physics, so the overall framing stays within reasonable popular-science simplification.
Sources used for verification
Academic/Peer-reviewed:
- Search for the Anomalous Events Detected by ANITA Using the Pierre Auger Observatory - aps.org
- A search for the anomalous events detected by ANITA using the Pierre Auger Observatory - arxiv.org
- Search for the Anomalous Events Detected by ANITA Using the Pierre Auger Observatory - pubmed.ncbi.nlm.nih.gov
- The Payload for Ultrahigh Energy Observations (PUEO): A White Paper - arxiv.org
Other reliable sources:
- Strange radio pulses detected coming from ice in Antarctica - psu.edu
- Strange radio pulses detected coming from ice in Antarctica - phys.org
- To find energetic particles from space, a new detector will soar over Antarctic ice - uchicago.edu
- The Vieregg Group: PUEO project description - uchicago.edu
- Astrophysics seminar: The Recent Flight of the Payload for Ultrahigh Energy Observations (PUEO) - illinois.edu
Fact-checked by Perplexity Sonar Pro on 2026-03-07
