Voyager 2 made its flyby of Uranus on January 24, 1986. With its robotic explorer more than two-and-one-half billion kilometers (about one-and-one-half billion miles) from Earth, JPL had to substantially improve the Deep Space Network's communications facilities in order to receive the craft's steadily declining signal.
NASA scientists were rewarded at Uranus with the discovery of two new rings and ten moons. Images of Miranda, the closest large moon to the planet, revealed an exceedingly strange surface. Parts of it were cratered like Earth's moon, while other parts looked as if they had been plowed with gigantic farm tools. The mission scientists had no explanation for this bizarre landscape.
Uranus, which appeared as an almost featureless green ball, turned out to have an unusual magnetic field that was offset from the planet's core by thousands of kilometers. This was possible only if Uranus had a very non-Earthlike internal structure, again leaving Voyager scientists without a compelling explanation for the planet's strangeness.
It took Voyager 2 three-and-one-half years to reach the last planet on its Grand Tour. The spacecraft passed a bare 4,500 kilometers (about 2,800 miles) above Neptune on August 25, 1989. As Voyager 2 approached, its images revealed that Neptune had an Earth-sized "great dark spot" like Jupiter's red spot, immersed in a similar, if less colorful, set of atmospheric bands.
The Voyager data also confirmed the existence of Neptunian rings. Mission scientists used these findings to determine that like Uranus, Neptune's magnetic field was offset far from the core. Unlike Uranus, Neptune had a source of internal heat, leading to the highest velocity winds of any planet. Finally, Voyager 2 imaged active nitrogen-ice volcanoes on Triton, the largest of Neptune's moons.
Uransus' moon Miranda reveals a complex geologic history in this view, acquired by Voyager 2 on Jan. 24, 1986. + Full image
Voyager 2's view of Neptune, 1989, with the Great Dark Spot. Below is the bright feature that Voyager scientists have nicknamed 'Scooter.' + Full image
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