Size & Distance
* Neptune has a diameter of 30,598 miles.
* It is about four times wider than Earth.
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* From an average distance of 2.8 billion miles from the Sun.
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* It takes sunlight 4 hours to travel from the Sun to Neptune.
Neptune
(more details below)
Geology
* Neptune is one of two ice giants in the outer solar system (the other is Uranus). Most (80% or more) of the planet's mass is made up of a hot dense fluid of "icy" materials – water, methane, and ammonia – above a small, rocky core.
* Of the giant planets, Neptune is the densest.
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* Scientists think there might be an ocean of super hot water under Neptune's cold clouds. It does not boil away because incredibly high pressure keeps it locked inside.
Atmosphere / Weather
* Neptune's atmosphere is made up mostly of hydrogen and helium with just a little bit of methane.
* Neptune is our solar system's windiest world. Despite its great distance and low energy input from the Sun, Neptune's winds can be three times stronger than Jupiter's and nine times stronger than Earth's. These winds whip clouds of frozen methane across the planet at speeds of more than 1,200 miles per hour. Even Earth's most powerful winds hit only about 250 miles per hour.
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* In 1989 a large, oval-shaped storm in Neptune's southern hemisphere dubbed the "Great Dark Spot" was large enough to contain the entire Earth. That storm has since disappeared, but new ones have appeared on different parts of the planet.
Orbit & Rotation
* One day on Neptune takes about 16 hours (the time it takes for Neptune to rotate or spin once). And Neptune makes a complete orbit around the Sun (a year in Neptunian time) in about 165 Earth years (60,190 Earth days).
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* Sometimes Neptune is even farther from the Sun than dwarf planet Pluto. Pluto's highly eccentric, oval-shaped orbit brings it inside Neptune's orbit for a 20-year period every 248 Earth years.
* Neptune can never crash into Pluto, because for every three laps Neptune takes around the Sun, Pluto makes two. This repeating pattern prevents close approaches of the two bodies.
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* Neptune’s axis of rotation is tilted 28 degrees with respect to the plane of its orbit around the Sun, which is similar to the axial tilts of Mars and Earth. This means that Neptune experiences seasons just like we do on Earth; however, since its year is so long, each of the four seasons lasts for over 40 years.