Few things bother scientists more than experimental readings that can’t be explained. They’ll go to great lengths to figure it out -- or sometimes, great heights. A century ago this month, for example, a young Austrian physicist soared miles high in a hot-air balloon to solve such a problem.

Twenty-eight-year-old Victor Hess was puzzled by flashes of energy seen inside small, sealed chambers. The chambers were empty, or they contained gases with no electric charge. Yet they still showed occasional sparks.

Many scientists thought the sparks were caused by the decay of radioactive elements in Earth’s crust. But some early experiments showed the sparks were more intense above the ground than on it.

Hess began his balloon experiments in 1911. He found that the number of electrical discharges was greater at high altitudes -- an indication that the source was beyond Earth.

He went up again on April 12th, 1912, during a total solar eclipse. The number of sparks remained high even when the Sun was eclipsed, so the source couldn’t be the Sun -- it had to be something outside the solar system.

Other scientists named these mysterious sparks “cosmic rays.” Hess won a Nobel Prize for the discovery. Yet the source of the cosmic rays remained mysterious.

Today, we know that cosmic rays are parts of atoms. Some come from exploding stars. But the source of the most powerful cosmic rays remains a mystery -- one that today’s scientists are going to great lengths to solve.

Script by Damond Benningfield, Copyright 2012