磁层鞘是在太空的行星磁层中介于磁层顶和弓形震波之间的区域。通常行星组织的磁场在磁层鞘的区域会因为太阳风的介入，因产生交互作用而变得不规则和减弱，并且不胜负荷的充满了被偏转的高能带电粒子。 在这个区域能观察到的粒子密度远比弓形震波之外为低，但大于在内侧的磁层顶，因此可以被视为是瞬间的过渡状态。

由于长久以来误解它只单纯的是弓形震波和磁层顶交互作用下的副产物，对磁层鞘内部确实本质的科学研究受到了限制，而没有注意它本身固有的性质。然而，近代的研究显示磁层鞘是一个有活力的区域，动荡喧扰的电浆流对弓形震波和磁层顶的结构也许扮演着重要的角色，并且也许可以支配高能粒子流穿越过边界。

The magnetosheath is the region of space between the magnetopause and the bow shock of a planet's magnetosphere. The regularly organized magnetic field generated by the planet becomes weak and irregular in the magnetosheath due to interaction with the incoming solar wind, and is incapable of fully deflecting the highly charged particles. The density of the particles in this region is considerably lower than what is found beyond the bow shock, but greater than within the magnetopause, and can be considered a transitory state.