A team led by the Southwest Research Institute is using NASA's New Horizons spacecraft to observe the solar wind as it travels to the outermost reaches of the solar system. The Solar Wind Around Pluto (SWAP) instrument has been tracking how this stream of charged particles slows down and changes as it moves farther from the Sun. These measurements could help pinpoint where the Sun's influence ends and interstellar space begins.
This question has puzzled scientists for decades. Understanding the transition zone between the solar wind and the interstellar medium sheds light on how our star interacts with the galaxy. The data from New Horizons, which famously flew past Pluto in 2015, offers a unique vantage point no other active mission can provide.
The SWAP instrument has been gathering data as New Horizons travels deeper into the Kuiper Belt. By measuring the density, temperature, and velocity of the solar wind at increasing distances, the team can map how it dissipates. The exact distances remain unconfirmed, but the trend is clear: the solar wind is thinning and slowing.
These findings refine models of the heliosphere, the protective bubble around the solar system. A better understanding of its boundary could improve predictions for how cosmic rays enter our neighborhood. That has practical implications for future deep-space missions and astronaut safety.
Some researchers caution that single-spacecraft measurements may not capture the full variability of the solar wind's behavior. Multi-point observations from other missions would strengthen the conclusions.