June 22, 2026 — Southwest Research Institute (SwRI) scientists are using a solar wind forecasting method combined with analytic and numerical heliosphere models to find out where the first plasma boundary of the outer heliosphere lies as NASA’s New Horizons spacecraft hurtles toward this mysterious region of space.
The heliosphere, a vast bubble of plasma created by the solar wind flowing outward from the Sun, surrounds the entire solar system and shields it from much of the high-energy galactic radiation found in interstellar space. Scientists believe the heliosphere resembles a comet because the Sun moves through the interstellar medium, creating a rounded “nose” region and a trailing “tail.” Other models predict a croissant-shaped heliosphere.
SwRI researchers are studying the heliosphere’s dynamic outer boundaries, including the termination shock and the heliopause, where the solar wind slows and then abruptly stops when interacting with interstellar material. These boundaries constantly expand and contract in response to changing solar conditions. During solar maximum, the “turbocharged” solar wind expands the heliosphere. During solar minimum, the ebbing solar wind allows the heliosphere to contract.
Two recent scientific papers are exploring how to accurately predict the location of the termination shock, particularly in the direction New Horizons is traveling.
After completing historic flybys of Pluto and Kuiper Belt object Arrokoth, New Horizons continues deeper into the outer solar system on a trajectory toward the heliosphere’s forward region. It will reach the termination shock and later leave the solar system, only the third spacecraftto do so after Voyager 1 and 2. Scientists hope to determine when the spacecraft will encounter this plasma boundary surrounding the solar system.
“We want to understand when the spacecraft will reach the termination shock to prepare to take measurements and download data about this region,” said Dr. Jonathan Gasser, lead author of the two papers. “Based on our research, we predict that New Horizons will encounter the termination shock as early as 2029 or as late as 2040. And it is possible that it could cross the boundary more than once as the heliosphere continues to expand and contract.”
The research could improve our understanding of how the heliosphere interacts with interstellar space and help future missions explore the boundaries between the solar system and the interstellar space beyond.
To read the Astrophysical Journal paper titled “Solar Wind Forecasting for Long-term Variations of the Global Heliosphere,” go to https://doi.org/10.3847/1538-4357/ae3152.
To read the Advances in Space Research paper titled “Predictions of New Horizons’ Termination Shock Crossing,” go to https://doi.org/10.1016/j.asr.2026.04.074.
For more information, visit Heliophysics or contact Mike W. Thomas, +1 210 522 2255, Communications Department, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238-5166.