Solar System Exploration: Planet Selector: Neptune

PLANET SELECTOR

ABOUT NEPTUNE

Dark, cold and whipped by supersonic winds, Neptune is the last of the hydrogen and helium gas giants in our solar system. More than 30 times as far from the Sun as Earth, the planet takes almost 165 Earth years to orbit our Sun. In 2011 it will complete its first orbit since its discovery in 1846.
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Featured Mission: Voyager 2
Most of what we know about Neptune is thanks to Voyager 2's 1989 flyby. The spacecraft discovered six of Neptune's moons.
Read More About Voyager 2 >>

VITAL STATISTICS

Average Distance from Sun:	4,498,252,900 km (2,795,084,800 miles)
Diameter:	49,248 km (30,601 miles)
Volume:	57.744 x Earth's
Mass:	102,430,000,000,000,000,000,000,000 kg (17.15 x Earth's)
Length of Day:	16.11 hours
Length of Year:	164.79 years
Known Moons:	13

SIZE & DISTANCE

If the Sun was as tall as a typical front door, Earth would be the size of a nickel - and Neptune would be about as big as a baseball.

Average Distance from the Sun: 4,498,252,900 km (30.06 A.U.)

EXTREME SPACE

Today's Forecast: Windy, Wild and Weird
Neptune is our solar system's windiest world. Winds whip clouds of frozen methane across the planet at speeds of more than 2,000 km/h (1,200 mph) - close to the top speed of a U.S. Navy F/A-18 Hornet fighter jet. Earth's most powerful winds hit only about 400 km/h (250 mph).

No Need for Sunscreen
Neptune is so far from the Sun that high noon on the big blue planet would seem like dim twilight to us. The warm light we see here on our home planet is roughly 900 times as bright at sunlight on Neptune.

Who You Calling Little?
Even though Uranus and Neptune are much smaller than our solar system's two other giant gas planets, you could still pack nearly 60 Earths inside each. Some storms in Neptune's clouds are as big as Earth.

Nowhere Land
Trying to land on Neptune is a really bad idea. Like the other three giant planets, it is a big ball of gas that gradually becomes a hot liquid well below the clouds. There's nothing on which to land. Anyone foolish enough to drop below the cloud tops would be torn by intense winds, frozen by super cold temperatures and eventually smashed by the sheer weight of the atmosphere above, which, by the way, is poisonous to humans.

Singin' Those Methane Blues
Even though it is only a small part of the atmosphere, methane gas is what gives Neptune its blue hue. Methane absorbs red light so when we look at Neptune, all we see is blue that is not absorbed.

Wrong Way Moon
Triton, Neptune's largest moon, has a weird, backward orbit that has it inching closer to Neptune each year. When the two finally collide, the moon will be shredded into beautiful rings that may rival those of Saturn. Don't wait up, though. The collision won't occur for another 10 to 100 million years.

TIMELINE

1845 - Mathematicians predict the existence of a planet beyond Uranus. Neptune was discovered a year later, increasing the number of known planets to eight. Neptune's first moon, Triton, is discovered 17 days later. It will be more than a century (1949) before another moon is discovered.

1979-1999 - Pluto's egg-shaped orbit brings it slightly closer to the Sun than Neptune for 20 years. The crossovers happen roughly every 248 years.

1984 - Astronomers discover Neptune's partial ring system while watching the planet pass in front of a distant star.

1989 - Voyager 2 becomes the first and only spacecraft to visit Neptune, passing roughly 4,800 km (3,000 miles) above the planet's north pole. The spacecraft discovers six new moons.

2002-2003 - Astronomers discover five new moons of Neptune, bringing the gas giant's total known moon count to 13.

2004-now - In 2000, Astronomers observing with the Keck II Telescope show Neptune having an upper atmosphere rich with moving features similar to those present around Jupiter. In 2011, Neptune will complete its first 165-year orbit of the sun.

SLIDE SHOW

Neptune
Neptune's stormy atmosphere
Neptune's rings
Neptune's Great Dark Spot
Massive cloud formations
Sun-blocking haze revealed
Wild weather in action
Neptune's moon, Triton
Triton in detail
View from beyond Neptune and Triton

MOONS

Neptune has 13 known moons. There are likely more captured in the planet's powerful gravitational grip, but it is extremely difficult to see small objects at such a great distance from Earth. Six of the moons were discovered when Voyager 2 arrived at Neptune in 1989. Triton is one of Neptune's most intriguing moons. It is the coldest place in our solar system with average temperatures of -235° C (-315° F).