The surface of Uranus may look as motionless as that of a snooker ball, but in reality the planet is no less turbulent than Jupiter and Saturn. Like its larger neighbours, Uranus does have bands of clouds that blow around the planet at incredible speeds, but because of an overlying layer of methane in the upper atmosphere, they are very faint. Only enhanced infrared pictures, like those taken by the Voyager space probe (right), show the weather on Uranus.
Uranus is one of two ice-giant planets in the solar system. Like Neptune, the other ice giant, it is sometimes also called a gas giant. Information about Uranus comes mostly from data gathered by NASA’s Voyager 2 spacecraft, which approached within 80,000 kilometers (50,000 miles) of the planet’s surface. Uranus does not display the type of geological activity associated with terrestrial planets such as Earth and Mars. The rings and moons of Uranus, however, do exhibit recognizable geological features.
Scientists report that between 80 percent and 85 percent of Uranus consist if an ice and rock mass. The ices are mostly frozen water, ammonia and methane around a liquid core. An envelope of hydrogen and helium, with traces of methane and ammonia, forms the planets’ atmosphere. Extreme temperatures and pressures in the planet’s interior could convert the carbon content of methane into diamond. According to space researchers Mona Delitsky, from California Specialty Engineering and Kevin Baines from the University of Wisconsin, Madison, the temperature at Uranus’ core could be 5,727 degrees Celsius (10,340 degrees Fahrenheit). This temperature could produce diamonds the size of a hand that precipitate from the liquid.
Thirteen rings have been identified around Uranus. These consist of a combination of ice and rock and are replenished with dust from meteor impacts — also called space weathering — on Mab, one of Uranus’ small outer moons. Some could be Centaurs, captured asteroids that orbit the sun together with Uranus, or comets. Uranus’ 27 identified moons appear to be made of ice and rock. The satellite system is chaotic and unstable. Astronomers predict that within a few million years, the moons could collide.
All of Uranus’ moons consist of ice and rock. Miranda and Ariel, two of the planets smaller moons, have features that indicate ongoing geological activity. Miranda’s diameter is just 450 kilometers (281 miles), yet it has surface fault scarps 10 kilometers (6 miles) high. Ariel, which has an 1,160 kilometers (725 miles) diameter, has canyons that could be between 3 and 5 kilometers (1.9 to 3.1 miles) deep. Miranda has areas of concentric fractures with surface volcanism called coronae, while the Ariel surface has ridged and smooth plains with surface volcanism. The extruded material could be ammonia and water ices that were melted by tidal heating of the moons’ interiors.