About 60 miles off the southernmost tip of Sicily, in the deepest section of the Mediterranean Sea, strange objects seem to grow. About every 330 feet, you’ll find few cables anchored to the seafloor, each pulled by a buoy close to half a mile straight up and strung with 18 glass spheres. 

The spheres, each of which is a little bigger than a basketball, make up a gigantic, underwater particle detector. This is ARCA, a prototype for the even larger, planned KM3NeT detector. 

ARCA was built to help scientists detect neutrinos, mysterious particles that are always passing through us and only rarely interact. But when they first fired up their prototypes in 2005, scientists discovered something else.

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