Download Uranus and Neptune are extremely cold.

s8pe-41303-ca
10/28/05
12:41 PM
MAZER
Page 432
Uranus and Neptune are extremely cold.
The seventh and eighth planets from the Sun are Uranus and Neptune.
These planets are similar in size—both have diameters roughly one-third
that of Jupiter. Unlike Jupiter and Saturn, Uranus and Neptune are
only about 15 percent hydrogen and helium. Most of the mass of each
planet is made up of heavier gases, such as methane, ammonia, and
water. As a result, Uranus and Neptune are more dense than Jupiter.
Uranus is a smooth bluegreen in visible light.
The small infrared image
shows that the pole facing
the Sun is warmer than
the equator.
Uranus looks blue-green, and Neptune appears deep blue. The
color comes from methane gas, which absorbs certain colors of light.
Each planet has methane gas above a layer of white clouds. Sunlight
passes through the gas, reflects off the clouds, then passes through the
gas again on its way out. The gas absorbs the red, orange, and yellow
parts of sunlight, so each planet’s bluish color comes from the remaining
green, blue, and violet light that passes back out of the atmosphere.
rings
pole
Uranus
Uranus is about twice Saturn’s distance from the Sun. The farther
a planet is from the Sun, the more slowly it moves along its orbit.
The greater distance also results in a larger orbit, so it takes Uranus
84 Earth years to travel around the Sun.
Like the other gas giants, Uranus has a system of rings and moons
around its equator. The ring particles and moons orbit Uranus in the
same direction as the planet’s spin. Unlike the other planets, Uranus
has an axis of rotation that is almost in the plane of its orbit.
As a result, Uranus seems to spin on its side. During a
solstice, one pole of Uranus points almost straight
toward the Sun.
Some scientists think that there was a
large collision early in Uranus’s history.
The result left the planet and its system
spinning at an unusual angle.
Uranus
Each pole of Uranus experiences more than 40 years
of sunlight and then more than 40 years of darkness
as the planet orbits the Sun.
Mass 15 Earth masses
Diameter 4 Earth diameters
Average distance from
Sun 19 AU
432 Unit 4: Space Science
Orbits in 84 Earth years
Rotates in 17 hours
PDF