Introductory Astronomy: The Planet URANUS

Basic Facts:
Average distance from Sun: 19.2AU
Period of revolution about Sun: 84 years
Period of rotation: 17.2 hours
Radius: 4.0 Earth radii
Mass: 14.5 Earth masses
Average Density: 1.2 g/cm^3
Magnetic Field: 100 times Earth's, highly inclined
Surface features: fairly featureless, rings, moons
Atmosphere: 84% H2, 14% He, 2% methane
Temperature: -355 degrees Fahrenheit

Uranus' blue-green color is due to the traces of methane in its atmosphere. Methane absorbs heavily the red wavelengths, reflecting the green and blue light and giving the planet its overall appearance. Its surface is nearly featureless; it lacks the band structure of Jupiter and Saturn (probably because it is very cold and has little heat flow).

The rings of Uranus are 100 to 1000 times more substantial than Jupiter's ring; still, they contain less mass than all of the thin material in Cassini's division (the largest gap in Saturn's rings). 11 rings have been discovered in all; all are very narrow. An interesting feature of Uranus' rings is that they are black. The particles which make up Uranus' rings are much larger than those that make up Saturn's. (They are probably boulder-sized.)

Uranus has 15 moons in all. Ten are low-density, icy (methane ice), cratered rocks, which are black like the rings. The five major moonsare larger and cratered. Some have features which were probably formed by flowing methane ice and faults. Some of the moons even have cliff features.