Figure 11.7 Uranus's strange magnetic field.

electrons and protons, in radiation belts that circle the planet. As these particles travel back and forth between the magnetic poles, they emit radio waves. Voyager 2 detected these waves, but they are weak and cannot be detected from Earth.

Uranus's magneto tail as measured by Voyager 2 was found to extend 10 million kilometres out into space. Unlike the magneto tails of other planets, the magnetic field lines in Uranus's tail are cylindrical and appear wound around each other like a corkscrew. This is probably due to the strange axial tilt of the planet.

Before the visit of Voyager 2 to Uranus in January 1986, only five moons were known to orbit Uranus. These moons were discovered between 1787 and 1948 and they range in size from 471 km to 1578 km in diameter. Voyager discovered 10 more moons, all less than 50 km in diameter. Several of these tiny, irregularly shaped moons are shepherd satellites whose gravitational pull confines the rings of Uranus. Astronomers used Earth-based telescopes to find two more moons in 1997, and three more in


Table 11.4 Moons of Uranus

Name of moon

Distance (km)

Period (days)

Diameter (km)



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