Scientists also learn about processes that occur when a star explodes as a supernova. Most cosmic rays have energies between a few million and a few billion electronvolts. Secondaries form when primaries collide with atoms at the top of the atmosphere. The collision changes the primary and the atom into a shower of secondaries. Many secondaries then collide with other atoms, making more secondaries.
Some secondaries reach the surface and even penetrate deep into the ground.
No measurable amount of primaries reaches the earth's surface. Most primaries that reach the earth's atmosphere have traveled through the Milky Way for millions of years. Anomalous component means peculiar part of a group. Physicists gave anomalous component primaries this name when they were discovered in the early 1970's. The composition and behavior of these particles differed greatly from those of galactic and solar primaries, which had been identified by the late 1950's.