Composition of the local interstellar cloud from observations of interstellar pickup ions

Abstract

Observations of pickup ions give us a new method to probe remote regions in and beyond the heliosphere. Comprehensive and continuous measurements of H, He, N, O, and Ne especially with the Solar Wind Ion Composition Spectrometer on Ulysses, are providing a wealth of data that are used to infer the chemical and physical properties of the Local Interstellar Cloud (LIC) that surrounds our solar system. We present new results on the elemental composition and ionization state of the LIC. Comparing the abundance of He, N, O and Ne in the present day local interstellar medium to the corresponding solar system abundance of these elements we find that, contrary to expectations of overabundance of heavy elements in the LIC, these two compositions are about the same. This suggests that there has been little or no additional galactic evolution since the formation of the Sun 4.6 billion years ago, or that the materials in the solar system and in the LIC followed different evolutionary paths.