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Space^19

The biggest planet, Jupiter, is 11 times wider than

Earth. It is made mainly of hydrogen and helium.

Its rapid spin makes the clouds in its atmosphere

form bands, called belts and zones.

WHAT ARE THE GALILEAN MOONS?

Jupiter’s four largest moons were discovered

by Italian astronomer Galileo Galilei in 1610.

Ganymede is the largest moon in the

Solar System – it is 5,268 km (3,273 miles)

across. Callisto is the most heavily cratered

object in the Solar System, and Io is

the most volcanic. Europa is covered

with ice. Water below the ice may

support primitive life.

WHY IS MARS CALLED THE RED PLANET?

Mars appears reddish in Earth’s night sky. The planet was named after the

Roman god of war because its colour symbolizes fire, blood, and war. Close-up

photographs show that the Martian surface is a rusty red colour. This is because

there are iron compounds in the rocks and soil.

This rocky planet has a thin atmosphere and ice caps

at its poles. Strong winds can whip up dust storms that

cover the whole planet. All the water on Mars is frozen

into rocks – primitive life may once have formed there.

Diameter (width) at Equator 6,794 km (4,222 miles)

Average distance from Sun 227.9 million km (141.6 million miles)

Time to orbit Sun 687 days

Time to spin around own axis 24.63 hours

Mass 0.11 x Earth’s mass

Gravity 0.38 x Earth’s gravity

Average surface temperature -63°C (-81°F)

Number of moons 2 (Phobos and Deimos)

Diameter (width) at Equator 142,984 km (88,849 miles)

Average distance from Sun 778.4 million km (483.7 million miles)

Time to orbit the Sun 11.87 years

Time to spin around own axis 9.93 hours

Mass 318 x Earth’s mass

Gravity 2.36 x Earth’s gravity

Cloud-top temperature -110°C (-166°F)

Number of moons 63

WHAT IS MARS’S SURFACE LIKE?

Mars has polar ice caps, vast sandy deserts, heavily

cratered regions, and high volcanic ridges. It boasts

of the biggest volcano in the Solar System, Olympus

Mons, and the biggest canyon system, Valles Marineris.

FIND OUT MORE. Elements 160–161 • Storms 54 • Volcanoes 44

FIND OUT MORE. Extraterrestrial Life 22 • Volcanoes 44

MARS

Mars

JUPITER

Jupiter

4 ROCK-STREWN SURFACE

NASA’s Mars Pathfinder sent back

this view of the Martian surface

in 1997. It shows a variety of

small rocks scattered

in a kind of sandy soil.

Great Red Spot,

a hurricane three

times wider than

Earth, has been

raging for centuries

Ice caps made from

frozen carbon dioxide,

water, and dust cover

the poles

Brighter zones

are bands of

sinking gas

Dark belts are

regions where gas

is welling up

MARS DATA

JUPITER DATA

GANYMEDE

CALLISTO

IO

EUROPA

Mars

Jupiter