Why Study Interstellar Matter Very Close to the Sun?

Interstellar matter (ISM) sets the boundary conditions of the heliosphere and dominates the interplanetary medium. The heliosphere configuration has varied over recent history, as the Sun emerged from the Local Bubble and entered a turbulent outflow of cloudlets originating from the Scorpius-Centaurus Association direction. Several indicators suggest that the local interstellar magnetic field is weak and parallel to the galactic plane. Observations of the interaction products of the ISM with the heliosphere, such as pickup ions and anomalous cosmic rays, when combined with data on the ISM towards nearby stars, provide unique constraints on the composition and physical properties of nearby gas. These data suggest abundances in nearby ISM are subsolar, and that gas and dust are not well mixed at the solar location.