Neptune

Neptune is the eighth planet from the Sun and the most distant known planet in the Solar System. With a diameter of about 49,000 kilometers and a mass around 1.0 × 10^26 kilograms, it is classified as an ice giant, distinct from the gas giants by its higher proportion of volatile ices such as water, ammonia, and methane.

Its appearance is a deep blue color due to methane in the atmosphere. The planet experiences supersonic winds and large storms; it radiates more internal heat than it receives from the Sun. The atmosphere is predominantly hydrogen and helium, with methane contributing to the blue tint.

Neptune orbits at an average distance of about 30.1 astronomical units from the Sun and completes one orbit in roughly 164.8 years. Its rotation period is about 16 hours, giving it a relatively short day compared with Earth.

Neptune has a faint ring system and at least 14 known moons. The largest moon is Triton, which follows a retrograde orbit and is geologically active, showing cryovolcanism and plumes. The ring system includes arcs in the Adams Ring, with notable features named Liberté, Égalité, and Fraternité.

Neptune was predicted mathematically in 1846 by Le Verrier (independently supported by English scientists) due to perturbations in Uranus’s orbit. It was observed telescopically that year and named after the Roman god of the sea.

Voyager 2 flew by Neptune in 1989, providing most of the detailed data currently available. No dedicated orbital mission has followed since, though several mission concepts have been proposed for future exploration.