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2h ago

New Horizons Finds Solar Wind Slows About 13–15% by 58 AU

The result supports charge‑exchange pickup‑ion braking models that reshape estimates of the heliosphere’s outer boundary and improve forecasts of cosmic‑ray exposure for deep‑space missions.

Credit: NASA’s Goddard Space Flight Center Conceptual Image Lab
An SwRI-led study sheds light on the deceleration of the solar wind as it journeys away from the Sun and interacts with and picks up interstellar material. NASA’s New Horizons spacecraft measured the solar wind as it traveled from just beyond Uranus’ orbit into the outer Kuiper Belt (red shaded region), detailing the gradual slowdown caused by interactions with interstellar materials (red line). Credit Southwest Research Institute

Overview

  • The peer‑reviewed study published Tuesday reports that New Horizons’ SWAP instrument measured the solar wind at 58 AU as roughly 13 to 15 percent slower than the solar wind at 1 AU.
  • Researchers attribute the gradual deceleration to charge exchange between solar wind ions and incoming neutral interstellar atoms that become ionized and are carried as heavier 'pickup ions,' which add mass and slow the flow.
  • New Horizons’ measurements span about 21 to 58 AU and extend earlier Voyager and New Horizons comparisons that showed a 5–10 percent slowdown between 30 and 43 AU and a sharp ~46 percent drop at Voyager 2’s termination shock near ~84 AU.
  • The new in‑situ data are being combined with Voyager, IBEX, IMAP observations and SHIELD heliospheric models to better map the heliosphere’s shape and density and to refine how Galactic Cosmic Rays (GCRs) can enter the inner solar system.
  • Those improved maps matter for people and hardware because more accurate heliosphere and GCR forecasts will help plan radiation protection for astronauts, satellites, and spacecraft on missions beyond Earth’s magnetic shield.