A Data-Driven Model for the Long-Term Variations of the Heliospheric Boundaries

The variability of solar wind properties directly impacts the outer heliosphere, which is expected to exhibit a time-dependent structure, driving a significant impact on the solar modulation of galactic cosmic rays. In addition to the Voyager probes that provided in-situ measurements of the outer heliosphere's properties, the New Horizons mission is currently offering valuable experimental data as it approaches the termination shock. Moreover, remote sensing observations of the outer heliosphere via energetic neutral atom (ENA) fluxes from the Interstellar Boundary Explorer (IBEX) clearly indicate long-term variations in the heliospheric boundaries. Soon, the Interstellar Mapping and Acceleration Probe (IMAP) will also contribute high-accuracy ENA flux observations. By employing a semi-analytical approach to solve the solar wind dynamics throughout the heliosphere, we have developed a data-driven model that leverages available in-situ and remote sensing data from the outer heliosphere to estimate the long-term, time-dependent distance of the termination shock from the Sun and the width of the heliosheath. Our predictions align closely with Voyager observations, differing by only a few astronomical units (AU). This will enhance our understanding of cosmic ray modulation in the heliosphere.