Uranus has about 63 times the volume of earth and is nearly 15 times as massive. One especially unusual quality of Uranus is that it is tipped over on its side – the axis of rotation is tilted by almost 90 degree and lies almost in the plane of its orbit. For part of a Uranus year, one pole point toward the sun while the other pole is in darkness. At the other end of Uranus’ orbit the poles are reversed.
The moons and the thin rings of Uranus all lie in a disk that is in the same plane as the equator of Uranus. In essence, the orbits of Uranus’s moons are all tilted out of the plane of the solar system. Scientists suggest that early in its history, a massive object that tipped the planet over hit Uranus.
Ancient people did not know Uranus, Neptune, and Pluto because they were too faint to see with the naked eyes. The English amateur astronomer William Herschel discovered Uranus in 1781. Viewed through a telescope, Uranus looks like a featureless blue-green disk. The atmosphere is mainly hydrogen and methane gas, which absorbs the red part of sunlight very strongly. Uranus and Neptune are much smaller than Jupiter and Saturn, and yet they have similar densities. This suggests that they have lower percentages of light elements and more water in their interiors. |
