The IceCube Neutrino Observatory is hunting particles in Antarctica Martin Wolf, IceCube/NSF

Particles spotted by a giant balloon in Antarctica can’t be explained by our current understanding of physics, a thorough analysis has determined. Now the race is on to figure out what they are.

In 2006 and then again in 2014, NASA researchers using the Antarctic Impulsive Transient Antenna (ANITA), a balloon equipped with a particle detector, picked up a signal that didn’t make sense. They had spotted evidence of high-energy particles travelling at an angle suggesting they had just whizzed through the planet unimpeded.