Cosmic Clues

Last month astrophysicists at Stanford's Kavli Institute for Particle Astrophysics and Cosmology presented their latest results from NASA's Fermi Gamma-Ray Space Telescope's observations of supernova remnants. And they think those results add to a growing body of evidence that cosmic rays -- highly energetic protons that regularly slam into the Earth from space -- come from these distant remnants. Younger supernova remnants in particular have stronger magnetic fields, the theory goes, which means they can keep particles close by long enough to accelerate them to far greater speeds.

So that's one mystery surrounding cosmic rays that might be solved. Here's another: around the same time, a paper appeared on the arXiv by Italian physicist Alessandro de Angelis of the University of Udine, claiming that Austrian physicist Victor Hess should not be solely credited with the discovery of cosmic rays.

For those who don't know the story, in the early 20th century, scientists thought the ionizing radiation in the Earth's atmosphere came from the crust -- except the radiation levels increased the higher one went in the atmosphere. Hess designed an instrument for more accurately measuring radiation levels, mounted it onto a balloon, and then flew 5 kilometers into the sky, taking measurements all the way. And he concluded Earth's crust couldn't possibly be the source of cosmic rays; they had to come from outer space.

Hess won the Nobel Prize in physics in 1936 for this momentous discovery, but De Angelis points out that another scientist, Domenico Pacini, made the same discovery right around the same time. He didn't use a balloon: he went underwater instead, placing his instrument in a copper box and sinking it in the Bay of Livorno. His results: the radiation measured was significantly less than at the surface, so the Earth's crust could not be the source of cosmic rays.

De Angelis offers the very first English translation of Pacini's paper on this experiment, and points out that Hess and Pacini knew of each other's work. So why do we remember Hess, and not Pacini? Chalk it up to an unfortunate twist of fate. Pacini passed away in 1934 and the Nobel Prize cannot be awarded posthumously. So Hess alone was honored two years later. At least De Angelis' paper is helping to keep Pacini's memory alive.