By Ron Cowen
Dust grains in the outer solar system are the source of some of the cosmic rays that bombard Earth, planetary scientists report in the Oct. 30 Geophysical Research Letters. The grains are located in the Kuiper belt, which lies within the solar system beyond the orbit of Neptune and consists of comets and other icy objects from the solar system’s formation.
It’s the composition of certain cosmic rays that suggests they originate in the solar system, says Nathan A. Schwadron of the Southwest Research Institute in San Antonio.