Neptune Basics

Quick Facts

Average Distance from Sun: 
2,795,000,000 miles  
(4,500,000,000 kilometers)
30.1 AU

Length of Year: 
164 years, 288 days

Length of Day: 
16 hours, 7 minutes

Diameter at Equator:
30,765 miles  (49,530 kilometers)

Mass:
17.1 times Earth

Surface Temperature (in upper atmosphere):
-346¡F  (-210¡C)

Introduction

    Neptune is the eighth planet from the Sun.  It is the fourth largest planet in the solar system.  If Earth were the size of the ball used in playing Jacks, Neptune would be the size of a bocci ball.

    Neptune is one of the outer planets.  The others are Jupiter, Saturn, and Uranus.  Neptune can't be seen without a telescope.  Neptune wasn't discovered until 1846.  The planet remained a mystery until a space probe passed by in 1989.

    Neptune is a gas giant like its neighbors, Jupiter, Saturn, and Uranus.  Like them, Neptune is a large planet.  It does not have a solid surface.  It has a deep gaseous atmosphere.  It has a ring system.  Of all the planets, Neptune is most like Uranus.  The two are often called twins.  Both planets are about the same size.  They are surrounded by a bluish layer of clouds.  Neptune and Uranus are much smaller than either Jupiter or Saturn.

    Neptune has eight known moons.  The largest is Triton.  Triton is the coldest object in the solar system.  Unlike most moons, it has an atmosphere.

Compared to Earth

    Neptune is the smallest of the four gas giants.  However, it is much bigger than Earth.  Neptune's diameter is almost four times greater than Earth's diameter.  About 58 planets the size of Earth could fit inside Neptune.    Neptune's core takes up a little less than one third of the planet's diameter.  Earth's inner and outer cores take up over half of its diameter.  Neptune has a liquid mantle.  It takes up about two fifths of the planet's diameter.  Earth's mantle is just under half of its diameter.  Earth has a thin, rocky crust.  Neptune doesn't have a crust.  Above Neptune's mantle is a thick atmosphere.  The atmosphere takes up almost a third of the planet's diameter.  Earth has a very thin atmosphere.

   Neptune is much larger than Earth.  It doesn't have a lot of mass for its size though.  So, its gravity is just a little greater than Earth's.  A person who weighs 100 pounds (45 kg) on Earth's surface would weigh 112 pounds (50 kg) on Neptune.  Neptune doesn't have a solid surface.  The weight is calculated as if you were standing at the top of Neptune's atmosphere.  Move the slider below to compare weights.   The slider shows weight in pounds.  

  Sunlight takes 8 minutes to reach Earth. Neptune is over 30 times farther from the Sun than Earth is.  Sunlight takes 250 minutes to reach Neptune.  That's more than four hours!  Very little of the Sun's heat reaches Neptune.  The temperature at the top of the clouds is -346¡F (-210¡C).