Uranus. 0. Uranus. Discovered in 1781. 4 times larger than Earth (in radius). 14.5 times the mass of Earth. Faint rings, indirectly detected through occultations. Rotation axis inclined by 97 0 against the orbital axis: Uranus is “rolling” on its orbit.
Uranus was discovered by chance
Uranus recognized as a planet in 1781 by William Herschel
Like other gas giants: No surface.
Gradual transition from gas phase to fluid interior.
Mostly H; 15 % He, a few % Methane, ammonia and water vapor.
Cloud structures only visible after artificial computer enhancement of optical images taken from Voyager spacecraft.
Optical view from Earth: Blue color of methane
83% H2 15% He 2% CH4
Traces of N2, HCN, H2S, NH3, CO
Uranus has an atmosphere composed primarily of hydrogen, helium, and a few percent methane
Methane absorbs red light, giving Uranus its greenish-blue color
= flow less disturbed
(limit of probing)
more H2S, so no NH3 clouds?
Micrometeorites bring CO and H2O to the stratosphere.
Uranus may have a rocky core surrounded by a mantle of water and ammonia
Electric currents in the mantles may generate the magnetic fields of the planets
No metallic core → no magnetic field was expected.
But actually, magnetic field of ~ 75 % of Earth’s magnetic field strength was discovered:
Offset from center: ~ 30 % of planet’s radius!
Inclined by ~ 60o against axis of rotation.
Possibly due to dynamo in liquid-water/ammonia/methane solution in Uranus’ interior.
Uranus has five satellites similar to the moderate-sized moons of Saturn, plus at least 22 more small satellites
Miranda is a small satellite with a diameter of 470 kilometers (290 miles).
Its surface is unlike anything in the solar system with features that are jumbled together in a haphazard fashion. Miranda consists of huge fault canyons as deep as 20 kilometers (12 miles), terraced layers and a mixture of old and young surfaces.
The brightest moon of Uranus.
The surface is pock-marked with craters, but the most outstanding features are long rift valleys stretching across the entire surface. Canyons much like the ones on Mars appear in the pictures. The canyon floors appear as though they have been smoothed by a fluid.
The largest moon of Uranus. It is marked by a few large impact basins, but is generally covered with small craters and very rough rocks.
Characterized by an old, heavily cratered, and icy surface. The surface shows little evidence of internal activity other than some unknown dark material that apparently covers the floors of many craters.
The darkest satellite of Uranus. It is about the same size as Ariel and has about the same density. The surface appears to be old with large craters and does not change much from one location to another. Near the top is a puzzling bright ring called the fluorescent cheerio.