Physical Characteristic

 Size and Mass

Neptunes Equatorial diameter measures 49,528 km, with a polar diameter of about 48,682 km due to its oblate shape from rapid rotation. It means its radius is approximately 24,622 km.

Neptunes diameter is nearly 3.9 times wider compared to Earths equatorial diameter about 12, 756km allowing roughly 57 Earths to fit inside its volume. Neptunes mass is 1.02 × kg, or about 17 times Earths mass of 5.97 × kg.

 Composition: Neptune, an ice giant, has a layered composition dominated by helium in its outer layers, with increasing concentrations of heavier elements and compounds deeper inside.

The observable atmosphere consists mainly of 80% hydrogen (H2), 19% Helium (He), and 1.5-3% methane (CH4), which absorbs red light to give Neptune its deep blue hue. Trace amounts include water vapor, ammonia (NH3), and hydrocarbons like Ethane (C2H6) from methane photolysis.

A vast mantle of supercritical fluid makes up most of the planet’s mass, composed of water, ammonia (NH3), and methane (CH4), ices under extreme pressure, possibly forming superionic water and diamond rain from decomposing methane.

At the center lies a rocky core, about 1.2 times Earth’s mass, rich in iron (Fe), Nickel (Ni), and silicates (rocky materials like), under pressure up to 7 million bars and temperatures around 5,400 K.