The Payload for Ultrahigh Energy Observations (PUEO) mission was a balloon-borne payload which flew over Antarctica. The balloon gondola carried an array of radio frequency (RF) receivers, designed to measure RF signals from neutrinos passing through the Antarctic ice sheet. It was based on the Antarctic Impulsive Transient Antenna (ANITA), though PUEO used much more powerful detectors. PUEO was selected by NASA for funding under the Pioneers Program. and is led by the University of Chicago, with instrument and gondola elements developed and supported by a number of institutions. The initial month-long flight commenced in December 2025 during austral summer for near-continuous daylight and reliable circumpolar wind patterns around Antarctica. The balloon was launch from McMurdo Station’s Long Duration Balloon Facility.

Ultra-high energy neutrinos interact with ice, producing radio emissions through the Askaryan Effect. A stratospheric balloon can observe the entire Antarctic ice sheet providing an exceedingly large detector volume. These measurements are best at the highest energies (>10¹⁸ eV) and complement ground-based detectors such as IceCube which are attuned to lower energy neutrinos. PUEO also measured extensive air showers (EAS) from ultra-high energy cosmic rays interacting with the upper atmosphere.

Mission Characteristics

Payload

Science Highlights

• Detection and characterization of ultra-high energy neutrinos and cosmic ray events;
• Constraints on astrophysical models for neutron-neutron star mergers;
• Ultra-high energy events from short gamma-ray bursts.

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