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Neptune
Neptune orbits about 10 AU farther from the Sun than Uranus,
so you would expect it to be colder. However, Neptune has
about the same outside temperature as Uranus because it is
hotter inside.
Uranus is usually one smooth color, but light and dark areas
often appear on Neptune. Clouds of methane ice crystals
can form high enough in the atmosphere of
Neptune to look white.
Storm systems can appear in darker
shades of blue than the rest of the
planet. One storm, seen during the
flyby of the Voyager 2 spacecraft in
1989, was named the Great Dark
Spot. Unlike the huge storm on
Jupiter, the Great Dark Spot did
not stay at the same latitude. It
moved toward Neptune’s equator.
The winds there may have broken
up the storm. Images of Neptune
obtained a few years later with the
Hubble Space Telescope showed no
sign of the Great Dark Spot.
What are the white patches
often seen on Neptune?
Neptune
Neptune has a large moon
that orbits in a direction
opposite to Neptune’s rotation. Scientists think a giant
collision might have occurred
in Neptune’s past.
Mass 17 Earth masses
Diameter 4 Earth diameters
Average distance
from Sun 30 AU
Orbits in 164 Earth years
Rotates in 16 hours
High clouds cast shadows
on the layer below.
cloud
shadow
KEY CONCEPTS
CRITICAL THINKING
1. Which planet has a greater
mass than all the other planets
put together?
4. Compare and Contrast
Why do Jupiter and Saturn
show a lot of white, while
Uranus and Neptune are
more blue in color?
2. What do you see instead of a
solid surface when you look at
an image of a giant planet?
3. Which planets have rings?
CHALLENGE
6. Apply If Uranus had areas
of ice crystals high in its
atmosphere, how would its
appearance change?
5. Analyze Most of Saturn is
much less dense than most
of Earth. Yet Saturn’s mass is
much greater than Earth’s
mass. How can this be so?
Chapter 19: Our Solar System 675