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Uranus' upper atmosphere
Uranus' upper atmosphere (Click on the image for a larger view)

Radio emissions detected several days before closest approach provided the first conclusive indication that Uranus actually possesses an magnetosphere.

Not only does a Uranian magnetic field exist; it is intense and skewed with its axis tilted at a 60-degree angle to rotational axis. At Earth, by comparison, the two axes are offset by about 12 degrees.

The intensity of the magnetic field at Uranus's surface is roughly comparable to that of Earth's, though it varies much more from point to point because of its large offset from the center of Uranus. The magnetic field source is unknown; the electrically conductive, super-pressurized ocean of water and ammonia once thought to lie between the core and the atmosphere now appears to be nonexistent. The magnetic fields of Earth and other planets are believed to arise from electrical currents produced in their molten cores.

As at Mercury, Earth, Jupiter and Saturn, there is a magnetic tail extending millions of miles behind Uranus. Voyager measured the magnetotail to at least 10 million kilometers (6.2 million miles) behind the planet. The extreme tilt of the magnetic axis, combined with the tilt of the rotational axis, causes the field lines in this cylindrical magnetotail to be wound into a corkscrew shape.

Voyager 2 found radiation belts at Uranus of an intensity similar to those at Saturn, although they differ in composition. The radiation belts at Uranus appear to be dominated by hydrogen ions, without any evidence of heavier ions (charged atoms) that might have been sputtered from the surfaces of the moons. Uranus's radiation belts are so intense that irradiation would quickly darken (within 100,000 years) any methane trapped in the icy surfaces of the inner moons and ring particles. This may have contributed to the darkened surfaces of the moons and ring particles.

Voyager detected radio emissions from Uranus that, along with imaging data, helped narrow the planet's rate of rotation to about 17 hours, 14 minutes.

 
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