Whitepaper #328 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: basic research. Additional topics: outer heliosphere; emerging opportunities.
We outline open questions on the evolution of large-scale solar wind structures throughout the heliosphere. We recommend in-situ observations on an outward trajectory from the Sun of plasma, fields, suprathermal and energetic particles, interstellar dust, and gas. An Interstellar Probe mission would provide such measurements and enable the needed lead in understanding the solar wind evolution.