Internal Structure

 Neptune’s internal structure consists of three main layers: a dense central core, an extensive icy mantle, and an outer gaseous atmosphere, with no distinct solid crust like terrestrial planets.

The core is rocky, roughly Earth-sized (about 1.2 times Earth’s mass), made of iron, nickel, and silicates (e.g.,). It endures extreme conditions- pressures up to 7 million bars (700 GPa) and temperatures around 5,400 K- potentially dissociating compounds into elements like oxygen, carbon (forming diamonds), and hydrogen.

Above the core is less thick mantle (most of the planet’s mass) of supercritical water (), ammonia (), and methane () ices in a hot, slushy, convective state. This fluid layer, under immense pressure, conducts electricity and may produce diamond rain from methane breakdown, driving internal heat. 

Neptune generates a strong irregular magnetic field, tilted 46.9 degrees to its rotation axis and offset from the center, likely from dynamo action in the conductive mantle fluids.