Final answer:
Uranus and Neptune have cores of rock and ice that make up most of their mass, with atmospheres rich in compounds of carbon, nitrogen, and oxygen, unlike the gas giants. Uranus is featureless due to the absence of an internal heat source, while Neptune has visible thin methane cloud layers and a pale blue color due to the scattering of sunlight.
Step-by-step explanation:
The internal structures of Uranus and Neptune are fascinating and complex, differentiating them from the larger gas giants, Jupiter and Saturn. Unlike their larger siblings that are mostly hydrogen and helium, Uranus and Neptune are rich in compounds of carbon, nitrogen, and oxygen, which is an indication of their differing compositions. Both planets have a similar core made up of rock and ice, which constitutes a significant part of their mass, suggesting they were unable to gather as much hydrogen and helium during their formation. Neptune's upper clouds consist of methane, visible as a pale blue tinge, similar to Earth's atmosphere, while Uranus' atmosphere is mostly a featureless haze with very little visible cloud structure due to a lack of internal heat suppressing atmospheric movement.
Uranus does not have a significant internal heat source, which results in a very stable atmosphere with little visible structure. Neptune, however, despite having a similar basic atmospheric temperature, appears different. It has a thin layer of methane clouds at the top of the troposphere and possibly a layer of hydrogen sulfide ice below it. Both planets are many times more massive than Earth, with densities indicating a composition fundamentally different from Saturn and Jupiter.