Neptune

Like Earth and the other Jovian planets, Neptune has a strong magnetic field and a sizeable magnetosphere (the region of space where Neptune's magnetic field is dominant over the interplanetary field). Voyager 2 did not find definite evidence for the existence of Neptune's magnetic field until eight days before its closest approach to Neptune, when radio and plasma wave observations of magnetospheric phenomena were obtained. Voyager 2 entered Neptune's magnetosphere about seven hours before its closest approach to Neptune and remained inside the magnetosphere for about three days. The center of Neptune's magnetic field is offset by 0.55 Neptune radius (0.55N_R) from Neptune's center, and its magnetic axis is tilted 47° with respect to Neptune's rotation axis (Neptune's magnetic poles are 47° from its poles of rotation). In this way, Neptune's magnetic field is similar to that of Uranus (see Uranus), and is unlike the magnetic fields of Earth, Jupiter, and Saturn, in which the offsets from the planets' centers and the tilts to their rotation axes are much smaller.

Voyager 2 also detected radiation belts of charged particles trapped in Neptune's magnetosphere. They include protons, electrons, charged molecular hydrogen, and charged heliumions. The particle density was found to be even lower than that found in Uranus's magnetosphere. Neptune's rings and small nearby satellites affect the structure of the magnetosphere near Neptune. Triton affects the outer part of the magnetosphere; among other things, it is presumed to be the main source of the charged nitrogenions that are found there.