The above figure illustrates the major particle populations that will be observed by SIS, along with data collected by other missions such as IMP-8 . Galactic cosmic rays are discussed on the CRIS page, while SEPs and ACRs are discussed below. Solar Energetic Particles Solar energetic particles represent a sample of solar material that can be used to make direct measurements of the Sun's elemental and isotopic makeup, and can be used to study the most energetic acceleration processes that occur in our solar system. Although the sun contains the vast majority of solar system material, we have only limited direct knowledge of its elemental and isotopic composition. With its greatly improved collecting power over other instruments, it is hoped that SIS can make a major advance in our knowledge of SEP isotopic composition.
Arrows indicate upper limits.
Anomalous cosmic ray observations offer a unique opportunity to study a sample of matter from local interstellar space. Because the ACR component apparently represents a direct sample of the local interstellar medium, it carries important information about galactic evolution in the solar neighborhood since the formation of the solar nebula - information that can be obtained by comparing the isotopic composition of ACR nuclei with that of solar system abundances, including those measured by SIS in solar energetic particles. Ne isotopic ratio is lower than it is in galactic cosmic rays, implying that the GCRs contain a component rich in 22Ne. If SIS is to achieve the objectives of excellent mass resolution and large collecting power beyond that of previous instruments that have measured ACRs and SEPs, it must satisfy several design requirements. The contributions to this are similar to those in the CRIS physical description .