ANITA Spots Another Inverted Cosmic-Ray-Like Event

High-energy cosmic-ray particles constantly bombard Earth. When one of these particles collides with molecules in our atmosphere, it triggers a cascade of secondary particles, collectively known as a cosmic-ray air shower. But that isn’t the only way high-energy particles interact with Earth. On 28 December 2006, the balloon-borne Antarctic Impulsive Transient Antenna (ANITA) detected an “upward” air shower—a fountain of high-energy particles erupting from Antarctica’s icy ground. The team now reports the observation of a second such event, which occurred on 12 December 2014.