New Horizons Confirms 13-15% Solar Wind Slowdown at 58 AU as Interstellar Gas Adds Drag
Updated
Updated · Universe Today · Jul 6
New Horizons Confirms 13-15% Solar Wind Slowdown at 58 AU as Interstellar Gas Adds Drag
1 articles · Updated · Universe Today · Jul 6
Summary
New Horizons found the solar wind at 58 AU is 13% to 15% slower than at Earth’s orbit, giving fresh evidence that interstellar material is already affecting the Sun’s outer domain.
SWAP data show the slowdown builds with distance because incoming neutral interstellar atoms become ionized through charge exchange, adding mass to the solar wind and reducing its speed.
Earlier measurements from New Horizons and Voyager 2 at 30 to 43 AU showed only a 5% to 10% slowdown, matching models that predict a gradual weakening before the heliosphere’s outer boundary.
At roughly 85 AU, scientists expect New Horizons to approach the termination shock—where Voyager 2 saw a 46% speed drop at 84 AU—with a comparable encounter possible around 2029.
Those boundary measurements matter beyond heliophysics because the heliosphere helps regulate galactic cosmic rays that threaten astronauts on long-duration missions.