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Which types of ice are expected in Neptune’s deeper cloud layers?

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Clouds in Neptune's atmosphere — Neptune A photograph of clouds in Neptune's atmosphere, taken by Voyager 2 in August 1989. The view is from below the planet's equator, and north is up. The Great Dark Spot (center left) is 13,000 km (8,100 miles)—about the diameter of Earth—in its longer dimension. Accompanying it are bright, wispy clouds thought to comprise methane ice crystals. At higher southern latitudes lies a smaller, eye-shaped dark spot with a light core (bottom left). Just above that spot is a bright cloud dubbed Scooter. Each of these cloud features was seen to travel eastward but at a different rate, the Great Dark Spot moving the slowest.

In the deeper layers of Neptune’s atmosphere, the types of ice expected depend on the specific pressure levels and the chemical composition of the region.

Water Ice: Clouds composed of water ice are expected to occur at depths where the atmospheric pressure exceeds 100 bars.1
Other Potential Ices: While the visible upper atmosphere contains clouds of methane ice, and the main cloud deck is thought to consist of ammonia or hydrogen sulfide ice crystals, Neptune is believed to possess additional cloud layers at deeper levels. The specific composition of these deeper clouds is dependent on the relative concentrations of gases containing sulfur and nitrogen.1

It is important to note that while Neptune’s interior is thought to contain melted ices—including methane, ammonia, and water—these compounds are likely spread throughout the interior rather than existing as distinct, centrally condensed layers.2