Authors: Jamie M. Jasinski (NASA Jet Propulsion Laboratory), Corey J. Cochrane (NASA Jet Propulsion Laboratory), Xianzhe Jia (University of Michigan), William R. Dunn (UCL), Elias Roussos (Max Planck Institute for Solar System Research), Tom A. Nordheim (JHU Applied Physics Laboratory), Leonardo H. Regoli (JHU Applied Physics Laboratory), Nick Achilleos (UCL), Norbert Krupp (Max Planck Institute for Solar System Research) and Neil Murphy (NASA Jet Propulsion Laboratory).

The properties of Uranus’ complex magnetosphere cannot be understood without carefully considering the role of external forcing by the solar wind. Here we show that during the Voyager 2 crossing of Uranus’ orbital location at ~19 au, the spacecraft observed a series of passing corotating interaction regions during solar minimum. The dynamic pressure of the solar wind therefore varied significantly on a timescale of days and weeks. Just before Voyager 2 crossed the Uranian bow shock and made its flyby of the ice giant planet, the solar wind dynamic pressure increased by a factor of ~20. Therefore, just prior to the flyby, the Uranian magnetosphere became severely compressed which would drive magnetospheric dynamics and consequently affect the findings from this single flyby. This includes increasing energetic electron fluxes within the radiation belts as well as emptying the magnetosphere of its internal plasma, providing possible explanations for the major mysteries that have surrounded Uranus since the Voyager 2 flyby.