Like the other gas giants, Uranus lacks a surface, leaving it without a well-defined boundary between its atmosphere and the planetary interior. While it does not have a surface, Uranus does have a core composed of water, methane and ammonia and makes up 20 percent of its planetary radius.
Uranus has the second lowest planetary density of any planet in the solar system, an indication that it is composed mostly of ice. Neptune is the only planet farther from the Sun than Uranus, and it is its vast distance from the Sun that allows many of the chemicals that make up Uranus to exist in a solid form. Uranus is sometimes referred to as ice giant due to a planetary composition that differs from that of Saturn or Jupiter.
The atmosphere of the planet Uranus contains lower amounts of hydrogen and helium than the larger gas giants, but it also contains relatively large amounts of methane. The methane in its atmosphere absorbs colors in the red end of the spectrum of light, giving the Uranus its blue-green color. Uranus radiates very little heat into space, possibly due to an impact that occurred shortly after the planet's formation that may have carved out a portion of its core.