Neptune

Faraway Neptune was only discovered in 1846 and remained poorly known until Voyager 2 flew by in 1989. The probe revealed a cold, blue world encircled by rings and moons, with a surprisingly dynamic atmosphere.

core of rock and possibly ice core of rock and possibly ice

layer of water, methane, and ammonia ices atmosphere of hydrogen, helium, and methane gases layer of water, methane, and ammonia ices atmosphere of hydrogen, helium, and methane gases

THE pLANET's iNTERioR

Neptune has no solid surface; its visible surface is the top of its atmosphere. Inside, the planet is layered, with each layer merging into the next.

structure

Neptune is the smallest and most distant of the four gas giants. It is almost four times the size of Earth with a structure most like that of its inner neighbor, Uranus. Neptune's outer layer is its atmosphere, which is made mostly of hydrogen. Below is a deep layer of water and ices, and below this a core of rock and possibly ice. Due to the planet's fast spin, material is pushed outward to form a bulging equator.

Spin AND oRBiT

Neptune's path around the Sun is less elliptical than that of any other planet, except Venus. This means there is no huge difference between its closest (perihelion) and farthest (aphelion) distance from the Sun. Neptune's spin axis is not perpendicular to its orbit, but is tilted from the vertical by 28.3°.

northern fALL

northern

WiNTER SoLSTiCE

axis tilts from _ vertical by 28.3°

NORTHERN SUMMER SOLSTiCE

northern fALL

axis tilts from _ vertical by 28.3°

NORTHERN SUMMER SOLSTiCE

northern

WiNTER SoLSTiCE

Neptune orbits the I Sun every 164.8 years northern

SPRiNG EQUiNoX

Neptune orbits the I Sun every 164.8 years northern

SPRiNG EQUiNoX

atmosphere and weather

Even at 30 times farther from the Sun than Earth, Neptune is affected by the Sun's heat and light. The north and south poles point sunward in turn as Neptune orbits the Sun, and the result is seasonal change. Each season on Neptune lasts roughly 40 years. Yet the Sun's heat alone is not enough to drive the dark stormlike features and the ferocious equatorial winds. Perhaps the planet is warmed by internal heat.

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