The Voyager 2 flyby of Uranus in 1986 revealed an unusually oblique and off-centred magnetic field. This single in situ measurement has been the basis of our interpretation of Uranus’s magnetosphere as the canonical extreme magnetosphere of the solar system; with inexplicably intense electron radiation belts and a severely plasma-depleted magnetosphere. However, the role of external forcing by the solar wind has rarely been considered in explaining these observations. Here we revisit the Voyager 2 dataset to show that Voyager 2 observed Uranus’s magnetosphere in an anomalous, compressed state that we estimate to be present less than 5% of the time. If the spacecraft had arrived only a few days earlier, the upstream solar wind dynamic pressure would have been ~20 times lower, resulting in a dramatically different magnetospheric configuration. We postulate that such a compression of the magnetosphere could increase energetic electron fluxes within the radiation belts and empty the magnetosphere of its plasma temporarily. Therefore, the interpretation of Uranus’s magnetosphere as being extreme may simply be a product of a flyby that occurred under extreme upstream solar wind conditions.

1986 年旅行者 2 号飞越天王星时，发现了一个异常倾斜和偏心的磁场。这种单一的原位测量一直是我们将天王星磁层解释为太阳系的典型极端磁层的基础;具有莫名其妙的强烈电子辐射带和严重等离子体耗尽的磁层。然而，在解释这些观察结果时，很少考虑太阳风的外力的作用。在这里，我们重新审视旅行者 2 号数据集，以表明旅行者 2 号以异常的压缩状态观测到天王星的磁层，我们估计这种状态存在的时间不到 5%。如果航天器只提前几天到达，上游太阳风的动压将降低 ~20 倍，从而导致磁层配置截然不同。我们假设磁层的这种压缩可以增加辐射带内的高能电子通量，并暂时清空磁层的等离子体。因此，将天王星的磁层解释为极端可能只是在极端上游太阳风条件下发生的飞越的产物。