FAQs on Cosmic Rays. Introductory Article on this topic. The chemical composition of the cosmic rays provide a surprisingly rich source of such knowledge. The chemical composition of the solar system has been determined from a combination of spectroscopy on the Sun, studies of the solar wind, and by chemical analysis of meteorites, which are presumed to have a purer sample of the early solar system than terrestrial rocks. The composition of cosmic rays is important because cosmic rays are a direct sample of matter from outside the solar system and contain elements that are much too rare to be seen in spectroscopic lines from other stars .
Cosmic rays provide important information on the chemical evolution of the universe.
If we look at the elemental composition measured for cosmic rays and compare it to our best understanding of the composition of the solar system, we quickly see some large differences. Silicon is used as the reference because it is a common intermediate-weight element that is easy to measure. We see that there is less hydrogen and helium in the cosmic rays than in the solar system, we think because hydrogen and helium are harder to accelerate to high energies than heavier elements. We also see more cosmic ray elements between silicon and iron than in the solar system. The accepted reason for all the observed cosmic ray lithium, beryllium, and boron is that these are pieces of heavier cosmic ray elements, especially carbon and oxygen, that have had high speed collisions with the very tenuous gas in interstellar space.