Geography - The Solar System
The solar system consists of the eight planets and their satellites (or moon) and thousands of other smaller heavenly bodies such as asteroids, comets and meteors.
The eight planets in our solar system are commonly divided into two groups:
Inner Planets - Mercury, Venus, Earth, and Mars.
The inner planets are small and are composed primarily of silicate rock and iron.
Outer Planets - Jupiter, Saturn, Uranus and Neptune.
Uranus has the second most extensive ring system of the solar system after Saturn. The rings, which are very difficult to see from ground based observations, were first discovered in 1977 by measuring the intensity of a star as Uranus and its rings passed in front of it. There are 13 known rings with radii of 38,000km to 98,000km. They are comprised of ice and some darker material which results in them being much darker than the rings of Saturn.
Uranus has 27 known moons with sizes ranging from over 1500 km diameter down to under 20km. The moons consist of ice, rock and other trace elements. Some of the inner moons undergo gravitation interactions with each other which may in many millions of years lead to instabilities and collisions.
Neptune has a ring system comprised of three main rings with radii between 63,000 km and 42,000km which appear to have a clumpy structure in which they form arcs rather than complete rings. It is believed that gravitational effects from Neptune's moons may cause the clumping.
Moons - Triton
Uranus has 13 known moons of which Triton (2700km diameter) is the most significant. The next largest moon, Proteus, is only 420km in diameter. Triton is the only large moon to orbit in retrograde (e.g. in the opposite direction to most orbits) and is thought to be a captured object rather than created in orbit.