anita

ANITA, the Antarctic Impulsive Transient Antenna, is a balloon-borne radio telescope designed to detect ultra-high-energy neutrinos and cosmic rays by capturing coherent radio pulses produced by particle cascades in Antarctic ice or the atmosphere. The project uses long-duration balloons to survey large portions of the Antarctic continent from stratospheric altitudes.

The instrument carries an array of dual-polarization horn antennas and observes in a broad radio band, typically around 200 to 1200 megahertz. Flights last several weeks, with missions launched from bases in Antarctica. The system records nanosecond-scale radio pulses and uses timing, polarization, and geometry to infer the direction and origin of detected events.

ANITA relies on the Askaryan effect, whereby neutrino interactions in ice create particle cascades that emit coherent radio waves. The same technique can capture radio emission from extensive air showers produced by cosmic rays in the atmosphere, which can be reflected off the ice and detected by the antennas. The balloon’s high vantage point and wide field of view enable sensitivity to extremely large effective volumes and broad angular coverage.

Results from ANITA have established stringent upper limits on the flux of ultra-high-energy neutrinos, contributing important constraints on cosmogenic neutrino models. The mission has also detected numerous radio impulses associated with cosmic-ray air showers. Some flights reported events with properties that were challenging to reconcile with standard expectations, prompting discussion of possible explanations, including beyond-Standard-Model scenarios, though such interpretations remain under study.

ANITA is a collaboration involving NASA’s balloon program and multiple universities and laboratories. The project has flown four campaigns to date (ANITA-I through ANITA-IV), with ongoing analyses aimed at improving sensitivity and interpreting observations in the broader context of astroparticle physics.