Uranus

Unlike the gas giants Jupiter and Saturn, Uranus and Neptune are primarily composed of "ices" — water, ammonia, and methane — in their interiors, rather than just hydrogen and helium. These icy materials are compressed into a super-dense fluid state beneath their frigid, turbulent atmospheres.

Scientists believe that under the extreme pressures and temperatures deep within these ice giants, methane breaks down, and carbon atoms are compressed into solid diamonds that then "rain" down through the planets' mantles.