As a gas giant, Neptune is primarily made from hydrogen, measured at 80 percent of the atmosphere, with an additional 19 percent composed of helium. The remainder of the planet is mainly composed of small amounts of methane, hydrogen deuteride and ethane.
Neptune's outer atmosphere also contains ammonia, water and methane ice, and ammonia hydrosulfide. The core of the planet is composed of silicates, including iron and nickel. The gases in the atmosphere liquefy in the planet's mantle and may eventually crystallize as they near the intense heat of the core, where the temperature matches that on the surface of the sun.