Since Uranus is covered with clouds astronomers must use indirect methods to study beneath these cloud layers. Uranus has a density of 1.2 g/cm3, slightly higher than Jupiter or Saturn. This implies there is less hydrogen on Uranus than on the gas giants, but the density is not high enough to indicate much rocky material either. It is believed that Uranus has a rocky core about the size of Earth, surrounded by a deep liquid water ocean.

     The strangest thing about the planet Uranus is its orbital characteristics. Uranus is the only planet, other than Venus, to rotate backwards (retrograde motion) as compared to all the other planets. In addition, all the other planets have less than a 30 degree axial tilt. Uranus, however, has its equatorial plane tilted nearly 90 degrees to its plane of revolution. This means that during the 84 year orbit, the north pole points almost directly at the Sun for part of the orbit, then point away from the Sun during the other part of the orbit. On a planet closer to the Sun, this would have a devastating effect on the seasons, but Uranus is so far from the Sun that even this strange orbital tilt makes little difference in the overall temperature average of -200 C.

     Uranus joins the ranks of those planets which have rings. The Voyager 
 
 

spacecraft showed that the rings are considerably narrower than those of Jupiter and Saturn. Most of the ring material of Uranus is confined to about 9 narrow bands. The ring particles are kept confined partly because of shepherd satellites, whose gravitational force keep the particles from straying.