didn’t have enough mass to hold on to these very light gases. As a result, the hydrogen
and helium initially on these inner planets floated away into space. Only the Sun and the
massive outer planets had enough gravity to keep hydrogen and helium from drifting away.
All of the outer planets have numerous moons. All of the outer planets also haveplanetary
rings, which are rings of dust and other small particles encircling a planet in a thin plane.
Only the rings of Saturn can be easily seen from Earth.
Jupiter
Figure 25.20: This image of Jupiter was taken by Voyager 2 in 1979. The colors were later
enhanced to bring out more details. ( 3 )
Jupiter, shown inFigure25.20, is the largest planet in our solar system, and the largest
object in the solar system besides the Sun. Jupiter is named for the king of the gods in
Roman mythology. Jupiter is truly a giant! It is much less dense than Earth—it has 318
times the mass of Earth, but over 1,300 times Earth’s volume. Because Jupiter is so large,
it reflects a lot of sunlight. When it is visible, it is the brightest object in the night sky
besides the Moon and Venus. This brightness is all the more impressive, since Jupiter is
quite far from the Earth — 5.20 AUs away. It takes Jupiter about 12 Earth years to orbit
once around the Sun.