Magnetic fields at the solar wind termination shock

A transition between the supersonic solar wind and the subsonic heliosheath was observed by Voyager 1, but the expected termination shock was not seen owing to a gap in the telemetry(1-4). Here we report observations of the magnetic field structure and dynamics of the termination shock, made by Voyager 2 on 31 August - 1 September 2007 at a distance of 83.7 AU from the Sun ( 1 AU is the Earth - Sun distance). A single crossing of the shock was expected, with a boundary that was stable on a timescale of several days. But the data reveal a complex, rippled, quasi- perpendicular supercritical magnetohydrodynamic shock of moderate strength undergoing reformation on a scale of a few hours. The observed structure suggests the importance of ionized interstellar atoms shock.