Page 50 - Curriculum Visions Dynamic Book

The core
At the centre of the planet the pressure is about five million Earth atmospheres. However, the gravitational field is still not enough to make the core solid. Thus, although rock and ice probably make up 80% of the total mass of Uranus, they are likely to be well mixed with gases and not concentrated at the core. In fact, it is likely that Uranus has very little rocky core at all.
Uranus is the only one of the giant planets not
to radiate significantly more energy than it receives. Nevertheless, it actually sends out about the same amount of heat as it absorbs, making the radiation 10,000 times more than Earth (whose small mass lost most of its heat long ago).
The heat of Uranus was probably first created when the planet began to gather its mass of gas and concentrate it. Because Uranus is so huge, it was able to store the heat, although apparently less well than Jupiter and Saturn.
As a result, its core is now much colder than those of its bigger neighbors.
The magnetic field that spreads out from Uranus is a result of the churning over of liquids below the gaseous surface. In this case it is thought that the magnetism is generated relatively close to the surface. As the charged particles of the magnetic field interact with the solar wind, they generate an aurora. It stretches out behind the planet in the form of a corkscrewlike tail.
Satellites and rings
Uranus has at least 22 satellites, of which the five largest can be called moons. The four largest satellites are Ariel, Umbriel, Titania, and Oberon. Most of the smaller ones were discovered by the Voyager spacecraft missions.
 The moon Ariel, showing the riftlike features that suggest it may have been geologically active at one time.
 The filmy rings of Uranus are shown by these lines.
Gas
Liquid
 A suggested structure of Uranus. The rocky core may be nonexistent or very small.
Possible rocky core.
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