Uranus

Like Earth and the other Jovian planets, Uranus has a strong magnetic field which arises in its interior. Evidence for Uranus' magnetic field and magnetosphere (the region of space where the planet's magnetic field is dominant over the interplanetary field) was not found until January 22, 1986, two days before closest approach to Uranus, when radio noise from charged particles trapped in its magnetosphere was detected. Voyager 2 crossed into Uranus' magnetosphere on January 24 and remained inside it for 45 hours. Uranus' magnetic field was found to be quite strong but very unusual. First, Uranus' magnetic poles were found to be 58.6° from its poles of rotation, which is much greater than the tilts of the magnetic fields to the poles of rotation found for Earth (11°), Jupiter (9.6°), and Saturn (0°). Second, the center of Uranus' magnetic field was found to be offset from its center of mass by 0.3 of Uranus' radius, a much greater offset than those found for the above-named planets. One effect of this magnetic field offset is that the magnetic field strength at the cloud level in Uranus' atmosphere is expected to vary by factors of five to 10 depending on Uranian latitude and longitude. Radiation belts of charged particles trapped in Uranus' magnetosphere were detected. They consist mainly of low energy protons and electrons; very few heavy ions are detected. The particle densities in these radiation belts are low compared with those densities in the radiation belts of Earth and Jupiter, possibly because the large tilt of Uranus' magnetic field to the interplanetary magnetic field allows the solar wind to make convective sweeps of particles out of Uranus' radiation belts fairly frequently.