Scientists believe that there is a shock wave at the edge of the heliosphere where the solar wind runs into interstellar material and slows down. This shock wave can accelerate ions to energies of hundreds of MeV. After they are accelerated, the ions can re-enter the heliosphere as anomalous component cosmic rays. During low points in the sunspot cycle, there are more anomalous component primaries than galactic primaries in the heliosphere at energies below about 100 MeV. Anomalous component primaries are too weak to produce many secondaries. Scientists therefore did not discover them until the early 1970's, when spacecraft carried instruments that could detect them. Secondary cosmic rays Secondary cosmic rays include all types of subatomic particles.
Most secondaries are muons, which are similar to electrons, but more massive.
Physicists discovered many types of subatomic particles in secondary cosmic rays before building machines called particle accelerators to study high-energy particles. Secondaries slow down in the atmosphere. Only a small fraction of them reach the earth. Every minute, about six secondaries strike each square inch of the earth. Because of the earth's magnetic field, the concentration is lower near the equator than near the poles.