Editing Advanced Composition Explorer (section)

=== Elemental and isotopic composition of matter ===
A major objective is the accurate and comprehensive determination of the elemental and isotopic composition of the various samples of "source material" from which nuclei are accelerated. These observations have been used to:
* Generate a set of solar isotopic abundances based on a direct sampling of solar material;
* Determine the coronal elemental and isotopic composition with greatly improved accuracy;
* Establish the pattern of isotopic differences between [[Cosmic ray|galactic cosmic ray]] and [[Solar System]] matter;
* Measure the elemental and isotopic abundances of [[interstellar medium|interstellar]] and interplanetary "pick–up ions";
* Determine the isotopic composition of the "anomalous cosmic ray component", which represents a sample of the local interstellar medium.