Hurtling around the Sun are eight planets. Those closest to
the Sun – Mercury, Venus, our home planet Earth, and
Mars – are made of rock. The vast outer planets – Jupiter,
Saturn, Uranus, and Neptune – are called “gas planets”
because all we see of them is their gas. All eight travel
in the same direction around the Sun. The time
taken to make one circuit, or orbit, increases
with distance. Mercury takes just 88 Earth
days to orbit, while Neptune’s longer
journey takes 164.8 Earth years.Planets
138
(^1) JUPITER
The largest and most massive
planet, Jupiter is also the fastest
spinner, rotating once on its own
axis in less than 10 hours. This giant
world is made mainly of hydrogen
and helium, with a central rocky
core. A thin faint ring encircles
Jupiter, which also has a large
family of moons.
Jupiter’s visible
surface is the top of
a deep and thick
atmosphere
made from
bands of
swirling gas
1
138_139_Planets.indd 138 03/01/19 12:10 PM