Uranus, the seventh planet from the Sun, orbits in the outer solar system, about two billion miles (3.2 billion kilometers) from Earth. It is an enormous world – quadruple the diameter of Earth, with 15 times the mass and 63 times the volume.
Unvisited by spacecraft for more than 35 years, Uranus inhabits one of the least explored regions of our solar system. Although scientists have learned some things about it from telescopic observations and theoretical work since the Voyager 2 flyby in 1986, the planet remains an enigma.
It’s easy to divide the solar system into two large groups: an inner zone with four rocky planets and an outer zone with four giant planets. But nature is, as usual, more complicated. Uranus and Neptune, the eighth planet from the Sun, are vastly different from the others. Both are ice giants, composed largely of compounds such as water, ice, ammonia and methane; they are places where the average temperature is minus 320 to minus 350 degrees Fahrenheit (minus 212 Celsius).
