Anomalous cosmic rays and the local interstellar medium

Abstract

The anomalous component of cosmic rays comprises energetic particles which originate as neutral atoms in the Local Interstellar Medium (LISM). In 1991 it was discovered that these particles become trapped in the Earth’s magnetic field, with lifetimes which concentrate the particles to ∼500 times their interplanetary flux. This new ‘‘radiation belt’’ offers an opportunity for direct measurements of the isotopic composition of a number of elements from the LISM by a cosmic‐ray instrument in low‐Earth orbit. These measurements can be used to investigate how nucleosynthesis has evolved in the Galaxy and may offer clues to the circumstances surrounding the formation of the protosolar nebula.