Simplify the following text for a Grade 8 native English-speaking person.
Original: These nuclei together make up 99 % of cosmic rays , and solitary electrons ( much like beta particles , although their ultimate source is unknown ) constitute the remaining 1 % of the particles that make up galactic cosmic rays .
Simplified: Most of these particles are protons , but some of them are helium nuclei or electrons . Cosmic rays are not actually rays but particles that are moving very fast .