A team of researchers from the Southwest Research Institute, led by Heather Elliott, is leveraging New Horizons' Solar Wind Around Pluto (SWAP) instrument to study the solar wind's behavior at the edge of the Solar System. The goal is to better define where our star's influence gives way to interstellar space.
The SWAP instrument measures the velocity and density of charged particles streaming from the Sun. In the outer reaches, the solar wind slows down significantly as it interacts with the interstellar medium — a process scientists are now tracking in unprecedented detail from a distance of over 50 astronomical units.
New Horizons continues its extended mission after flying past Pluto in 2015 and Arrokoth in 2019. The spacecraft remains healthy, transmitting data from its unique vantage point, though transmission rates are limited due to its immense distance from Earth — each signal takes roughly seven hours to arrive.
This research addresses a fundamental question: where does the Solar System end? Defining the heliopause — the boundary where the solar wind meets interstellar plasma — has implications for understanding cosmic ray shielding and the structure of our galactic neighborhood. Previous missions like Voyager 1 and 2 crossed this boundary, but New Horizons offers a different trajectory and more modern instrumentation.
Counter_argument: Some planetary scientists argue that New Horizons' aging power supply and limited bandwidth constrain the resolution and frequency of its observations, making it difficult to capture short-term variations in the solar wind that could clarify boundary mechanisms.