A baffling cosmic mystery may have just deepened. In recent years, scientists with the Antarctic Impulsive Transient Antenna (ANITA) experiment reported detecting radio signals that appeared to travel upward through the Earth. This phenomenon seemingly defies the known laws of physics. These anomalous events hinted at the possibility of new particles or interactions not described by the Standard Model, the reigning theory of particle physics. However, a new, exhaustive search by a different experiment has failed to find evidence of such events, placing tight constraints on this exotic explanation.

In response to the ANITA findings, an international team operating the Pierre Auger Observatory in Argentina conducted a dedicated search for similar phenomena. The observatory, one of the largest cosmic-ray detectors in the world, uses a vast array of instruments, including a Fluorescence Detector. This detector is designed to spot the faint ultraviolet light produced during an “air shower,” a cascade of secondary particles generated when an ultra-high-energy particle from space collides with Earth’s atmosphere. Scientists specifically re-analyzed their data to look for air showers that appeared to be traveling upward, originating from below the horizon at extreme angles.

After sifting through 15 years of data collected between January 2004 and December 2018, the Auger team found only one candidate event. This lone detection is statistically consistent with the expected background noise — in this case, a standard, downward-traveling cosmic-ray shower that the system may have misidentified. The analysis predicted a background of approximately 0.27 such misreconstructed events over the search period, meaning the detection of one event is not scientifically significant and does not point to a new discovery.

The results from the Pierre Auger Observatory, published in Physical Review Letters, place the original ANITA observations in a new, more challenging context. Based on the energy and direction of the ANITA signals, scientific models predicted that the Auger Observatory should have detected a significant number of similar upward-going showers — more than eight events in the most conservative estimate. The fact that Auger found none, statistically speaking, creates a “strong disagreement” with the interpretation of the ANITA signals as upward-going air showers. While this new study does not solve the puzzle of what ANITA detected, it strongly suggests the answer is not a flux of exotic particles traveling through the planet, leaving the Antarctic anomaly an even greater enigma.

References

• Abdul Halim, A., Abreu, P., Aglietta, M., Allekotte, I., Almeida Cheminant, K., Almela, A., Aloisio, R., Alvarez-Muñiz, J., Ammerman Yebra, J., Anastasi, G. A., Anchordoqui, L., Andrada, B., Andringa, S., Apollonio, L., Aramo, C., Araújo Ferreira, P. R., Arnone, E., Arteaga Velázquez, J. C., Assis, P., … Pierre Auger Collaboration. (2025). Search for the anomalous events detected by anita using the pierre auger observatory. Physical Review Letters, 134(12), 121003. https://doi.org/10.1103/PhysRevLett.134.121003
• Naumova, M. & Pennsylvania State University. (2025, June 13). Strange radio pulses detected coming from ice in Antarctica. Phys.Org; Pennsylvania State University. https://phys.org/news/2025-06-strange-radio-pulses-ice-antarctica.html