Strange signals from outer space are constantly reaching Earth, hailing from sources like pulsars, quasars, and supernovas. In Antarctica, a signal like this recently seemed to materialize out of nowhere, but it wasn’t coming from the sky above—instead, it was coming from the depths of the ocean.
Two decades ago, far above the vast expanse of ice and snow, instruments aboard the Antarctic Impulsive Transient Antenna (ANITA) experiment (now retired) were picking up radio waves from cosmic rays shooting through the atmosphere. When those rays collide with particles in said atmosphere, they scatter into secondary particles—a hundred of which pass right through our bodies every second without our realizing it. By detecting these particles, ANITA was giving insight into distant cosmic events. But then, things got weird.
ANITA detected anomalous signals coming from below the horizon, at unusually sharp angles some 30 degrees below the icy surface. What appeared to be radio pulses had to have somehow penetrated thousands of miles of rock that they should have been absorbed by. How these ultrahigh-energy cosmic ray (UHECR) pulses could have been detected at all was a mystery. Physicist Stephanie Wissel of Penn State University, who had been scouring ANITA data for signals from neutrinos (which are already mysterious subatomic particles) had never seen anything remotely like it.
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