Robot Explorers: US Unmanned Space Missions

Robot Explorers: US Unmanned Space Missions: page 14

Four and a half years after visiting Saturn, Voyager 2 arrived at Uranus. Uranus, the third largest planet, is known as the one that was "knocked on its side". Scientists believe that Uranus was permanently thrown off its normal axis when it was struck by a body at least the size of Earth.

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Like other planets, it has rings and moons that orbit around its equator. The planet's blue color is due to methane in its atmosphere which absorbs all the other colors. About 5,000 miles below the cloud tops, there is believed to be a scalding ocean of water and dissolved ammonia some 6200 miles deep.

Prior to the arrival of Voyager 2, five moons had been counted and dark rings had been detected. Since Uranus is two billion miles away from Earth, only broad characteristics of the planet could be discerned.

Voyager 2 discovered a high layer of smog-like haze around the sunlit pole of the planet. A few methane clouds seen in the atmosphere revealed the presence of winds of nearly 375 miles per hour at the middle latitudes. Otherwise, the shallow hydrogen-helium atmosphere was relatively calm.

The smallest of the five Uranian moons known before Voyager 2, Miranda possesses diverse geologic features. Gigantic faults have sliced canyons as deep as 12 miles into the surface. Rolling plains that are heavily cratered back up to large stretches of grooved and ridged land. These characteristics suggest Miranda may have experienced strong tidal heating in the past. All such forces seem to have come to a halt, however.


Ariel and Titania both have valleys formed by faults. Titania's fault lines may be the result of the expansion of subsurface water as the moon's interior froze. Oberon and Umbriel have old surfaces little changed since their formation. Umbriel's surface is darker than those of its companions and may have been covered by a layer of dark debris.

Ten new moons were found orbiting near the rings, bringing the total to 15. Two new rings were discovered in addition to the nine that were already known. From the Uranian rings, scientists have determined that planetary rings may be short-lived phenomena that come and go throughout a planet's lifetime.

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	Copyright ©2004 Colleen Gino	Images courtesy JPL and NASA.