Matthew Francis, writing on Ars Technica:
Where exactly are those edges of the Solar System? According to theory, the boundary of the Solar System is marked by a region known as the heliopause, where the solar wind—particles streaming from the Sun—meets the plasma of interstellar space. In this region, beginning about 90 times the distance from Earth to the Sun, models predicted that the solar wind’s particles would be deflected by the interstellar material, much as water is pushed aside by the bow of a ship.
However, new measurements provided by the venerable Voyager 1 probe have failed to find the expected flow, deepening the mystery of the boundary between our Solar System and interstellar space. This adds to an earlier surprise, when Voyager’s instruments measured zero outward velocity in the solar wind, a measurement that has now held constant for over two years. In a Nature paper, Robert B. Decker, Stamatios M. Krimigis, Edmond C. Roelof, and Matthew E. Hill concluded that Voyager 1 is not actually close to the heliopause, despite expectations. The researchers further suggested that the models for interactions between the solar wind and interstellar plasma may require reevaluation.