Magnetopause and cusp observations at Neptune

Plasma and magnetic field measurements in a subsolar cusp region of Neptune are compared with two current models of cusp regions, stemming from earth measurements: (1) a cusp region filled with stagnant plasma separated from the magnetosheath by a tangential discontinuity and (2) a mantle layer of dynamic plasma separated from the sheath by a rotational discontinuity. The plasma observations are more consistent with the mantle-layer interpretation. However, because of the particular trajectory of the Voyager 2 flyby, it was not possible to distinguish the mantle and the stagnant cusp models on geometrical grounds.